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MORPHOLOGICAL CHARACTERIZATION OF TWO CUCHIA-
Monopterus cuchia (Hamilton, 1822) AND Ophisternon bengalense
(McClelland, 1844) FOUND IN INLAND WATER OF BANGLADESH
A Thesis
By
Examination Roll No. 10 Fish FBG JD 14 M Registration No. 36963
Session: 2010-2011 Semester: July-December, 2011
MASTER OF SCIENCE (M.S.) IN
FISHERIES BIOLOGY AND GENETICS
DEPARTMENT OF FISHERIES BIOLOGY AND GENETICS BANGLADESH AGRICULTURAL UNIVERSITY
MYMENSINGH
November 2011
MORPHOLOGICAL CHARACTERIZATION OF TWO CUCHIA -
Monopterus cuchia (Hamilton, 1822) AND Ophisternon bengalense
(McClelland, 1844) FOUND IN INLAND WATER OF BANGLADESH
A Thesis
By
Examination Roll No. 10 Fish FBG JD 14 M Registration No. 36963
Session: 2010-2011 Semester: July-December, 2011
Submitted to the Department of Fisheries Biology and Genetics Bangladesh Agricultural University, Mymensingh
in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE (M.S.)
IN FISHERIES BIOLOGY AND GENETICS
DEPARTMENT OF FISHERIES BIOLOGY AND GENETICS
BANGLADESH AGRICULTURAL UNIVERSITY MYMENSINGH
November 2011
MORPHOLOGICAL CHARACTERIZATION OF TWO CUCHIA -
Monopterus cuchia (Hamilton, 1822) AND Ophisternon bengalense
(McClelland, 1844) FOUND IN INLAND WATER OF BANGLADESH
A Thesis
By
Examination Roll No. 10 Fish FBG JD 14 M Registration No. 36963
Session: 2010-2011 Semester: July-December, 2011
Approved as to the style and contents by
...……………………………………... …...….………………………
Prof. Dr. Mostafa Ali Reza Hossain Prof. Dr. Md. Samsul Alam Supervisor Co-Supervisor
………………………….. Dr. Zakir Hossain
Chairman
Examination Committee and
Head, Department of Fisheries Biology and Genetics Bangladesh Agricultural University
Mymensingh
November 2011
ACKNOWLEDGEMENTS
All the praises and thanks to almighty God, who enabled the author with His enormous
blessings to complete the research work and thesis for the degree of Master of Science in the
discipline of Fisheries Biology and Genetics in due time.
The author sincerely expresses deepest sense of gratitude and immense indebtedness, profound
regard, deep sense of respect to her respected teacher and research supervisor Dr. Mostafa Ali
Reza Hossain, Professor, Department of Fisheries Biology and Genetics, Bangladesh
Agricultural University, Mymensingh for his unconditional love, scholastic guidance,
continuous suggestion, constant inspiration and sincere supervision of her research work. His
regular advice and valuable supervision helped the author to complete the thesis.
The author greatly indebted to her co-supervisor Dr. Md. Samsul Alam, Professor, Department
of Fisheries Biology and Genetics, Bangladesh Agricultural University, Mymensingh, for his
valuable suggestions, constructive direction, affectionate encouragement, and kind cooperation
in performing the research activities precisely.
The author pleasure to expresses her heartiest gratefulness to Dr. Zakir Hossain, Head,
Department of Fisheries Biology and Genetics, Bangladesh Agricultural University,
Mymensingh, for his inspiration, valuable suggestions and generous help during the period of the
experiment.
The author is proud to acknowledge her gratefulness and boundless gratitude to her honourable
teachers of the Department of Fisheries Biology and Genetics, especially Professor Dr. Md.
Fazlul Awal Mollah, Professor Dr. Md. Rafiqul Islam Sarder, Professor Dr. Md. Mukhlesur
Rahman Khan, Associate Professor Dr. Md. Sadiqul Islam, Assistant Professor Dr. Mohd. Golam
Quader Khan and Lecturer Mr. A. K. Shakur Ahmed for their constant inspiration, generous help
and illuminating suggestions in many ways for completing the research work and preparation of
the thesis.
The author wishes to express her deepest sense of respect to all the teachers of the Faculty of
Fisheries, Bangladesh Agricultural University, Mymensingh, for their valuable teaching,
suggestion and encouragement during her study period at the University.
The author also expresses her honest and heartfelt gratitude and special thanks to her respected
teachers of Faculty of Fisheries, Hajee Mohammad Danesh Science and Technology University,
Dinajpur for their help, affectionate encouragement, cordial feelings, brilliant advice and fruitful
suggestions and kind co-operation at every step to complete her B. Sc. Fisheries (Hons.) degree.
The author expresses her cheerful acknowledgement to her well wisher and elder brother Dr. Md.
Nahiduzzaman, Ex PhD fellow, Department of Fisheries Biology and Genetics, BAU,
Mymensingh for his continuous encouragement and kind cooperation throughout the period of
the research work and preparation of the thesis. The author is also grateful to elder brother
Pankoz Kumar Roy, Department of Fisheries Biology and Genetics, BAU, Mymensingh for his
affectionate encouragement, continuous help and kind co-operation during the research period
and completion of the thesis.
The author offers her sincere thanks to Anis bhai, Jakaria bhai and other laboratory attendants of
the Department of Fisheries Biology and Genetics, BAU, Mymensingh for their active
cooperation and overall assistance during the whole study period.
The author expresses her cordial thanks and gratitude to all of her sweet surroundings and
beloved friends and well wishers specially Krishna, Shipra, Munmun, Nishu, Shamole, Maya,
Konica, Munni, Imran, Shuvo, Himel, Rakhi, Kollol, Wahed, Naznin, Shilpi, Tonusree, Momo,
Suma, Lipi and all other friends for their kind cooperation and inspiration throughout the study
period and research work.
Finally, the author would like to acknowledge with great regards and pleasure, deepest sense of
gratitude and immense indebtness to her beloved parents Rajendra Nath Roy and Shikha Rani
Roy, dear elder brothers and sisters especially Tapan, Dhananjoy and Nondita, beloved nephew
Kabya and other relatives for their blessing, countless sacrifice and endless inspiration
throughout her life. The deepest and most sincere appreciation is also due to her late grandfather
and grandmother and all other well-wishers for their endless patience, sacrifice, encouragement
which made everything possible in her life.
November 2011 The Author
CONTENTS
CHAPTER TITLE PAGES
ACKNOWLEDGEMENTS
iv-v
CONTENTS vi-vii
LIST OF TABLES viii-ix
LIST OF FIGURES x-xi
ABSTRACT xii
I INTRODUCTION 1-9
1.1 Importance of Fisheries in Bangladesh 1 1.2 Description of two eels and distribution 2-5
1.3 Global importance 5 1.4 Importance in Bangladesh context 6-7 1.5 Aquaculture potential 8 1.6 Justification of the study 8-9
1.7 Objectives 9
II REVIEW OF LITERATURE 10-20
III MATERIALS AND METHODS 21-27
3.1. Collection of sample 21
3.2. Rearing of sample 22
3.3. Measurement of morphometric and meristic characters
3.3.1 Morphometric characters
3.3.2 Meristic characters
22-25
22-24
24-25
3.4. Land mark distances of the species 25
3.5. Dissection of the species 25
3.6. Statistical analyses 26-27
CONTENTS (Contd.)
CHAPTER TITLE PAGES
IV RESULTS 28-46
4.1 Length and body weight of M. cuchia and O.
bengalense and their sexing pattern 28
4.2 Physical characteristics 29-33
4.3 Meristic characters 34
4.4 Morphological and landmark differences 35-46
V DISCUSSION 47-53
VI SUMMARY AND CONCLUSION 54-56
REFERENCES 57-65
LIST OF TABLES
TABLE TITLE PAGES
3.1. The morphometric characters measured
22-23
3.2. The meristic characters of eels 24
4.1
Length and weight of M. cuchia and O.
bengalense and their sexing pattern (SD =
standard deviation, n = number of fish) and the
range
28-29
4.2 Comparison of meristic counts between M. cuchia
and O. bengalense (Mann-Whitney U) (minimum
and maximum values are in parenthesis)
34
4.3
Comparison of adjusted morphological and
landmark measurements between sexes of M.
cuchia (Mean ± SD)
35-37
4.4 Comparison of adjusted morphological and
landmark measurements between sexes of O.
bengalense (Mean ± SD) (Independent samples t-
test)
37-38
4.5 Means and standard deviation of adjusted
morphological data for M. cuchia and O.
bengalense (t-test for difference before and after
adjustment of the variables)
39 -40
4.6
Univariate statistics (ANOVA) testing difference
between M. cuchia and O. bengalense (df1=1;
df2=47)
41-42
LIST OF TABLES (Contd.)
TABLE TITLE PAGES
4.7
Contribution of morphometric and truss
measurements of M. cuchia and O. bengalense to
the canonical functions
43
4.8 Correct classifications of individuals M. cuchia
(collected from Mymensingh and Dinajpur) and
O. bengalense (collected from Satkhira and
Bagerhat) into their original population (leave-
one-out-classification)
46
LIST OF FIGURES
FIGURE TITLE PAGES
1.1. Photograph of the mud eel, Monopterus cuchia
(Hamilton,1822)
2
1.2.
Photograph of the swamp eel, Ophisternon
bengalense (McClelland, 1844)
4
3.1. Map of Bangladesh showing sampling sites of M.
cuchia and O. bengalense.
21
3.2. Morphometric measurement
24
3.3 Six landmarks determining 8 distances on eel body 25
4.1
Body colour (ventral view-left and dorsal view-
right) of M. cuchia
29
4.2 Body colour (ventral view-left and dorsal view-
right) of O. bengalense
30
4.3 Head shape of M. cuchia
30
4.4 Head shape of O. bengalense
30
4.5 Head shape (ventral side) of M. cuchia 31
4.6 Head shape (ventral side) O. bengalense 31
4.7 Lines present beside lateral line in M. cuchia (left)
and no line present in O. bengalense (right)
31
4.8
Tail shape of M. cuchia (left) and O. bengalense
(right)
32
LIST OF FIGURES (Contd.)
FIGURE TITLE
PAGES
4.9
Gill arch of M. cuchia (left) and O. bengalense
(right)
32
4.10
Mouth gape of M. cuchia (left) and O. bengalense
(right)
33
4.11
Teeth of M. cuchia (left) and O. bengalense (right)
33
4.12
Fat like organ in the stomach of O.bengalense
33
4 .13
Sample centroids of discriminant function scores
based on morphometric and truss measurements
(1. M. cuchia (collected from Mymensingh), 2. M.
cuchia (collected from Dinajpur), 3. O. bengalense
(collected from Satkhira), and 4. O. bengalense
(collected from Bagerhat)
44
4.14 Dendrogram based on morphometric characters
and landmark distances - 1. M. cuchia
(Mymensingh), 2. M. cuchia (Dinajpur), 3. O.
bengalense (Satkhira) and 4. O. bengalense
(Bagerhat)
45
ABSTRACT Morphometric comparison was carried out to evaluate the population status of two eels-
Monopterus cuchia and Ophisternon bengalense collected from four different stocks.
Morphometric, truss measurements and meristic characters from thirty two M. cuchia
(collected from Mymensingh and Dinajpur), seventeen O. bengalense (from Bagerhat and
Satkhira) were analyzed. The mean number of line below head were significantly (Mann-
Whitney U test; z= -6.091; P<0.001) different between two species out of five meristic
characters. Significant differences were observed in eleven morphometric characters Pre
dorsal length (PDL), Post dorsal length (PoDL), Post anal length (PoAL), Head length
(HL), Snout length (SnL), Upper jaw length (UJL), Lower jaw length (LJL), Head width
(HW), Pre orbital length (PrOrL), Least body diameter (LBD) and Highest body diameter
(HBD) and one truss measurement (3-5) between two species in varying degrees. Plotting
discriminant function DF1 and DF2 showed a clear differentiation between the species as
well as between the stocks for both morphometric and landmark measurements. For both
morphometric and landmark measurements, the first and second DF accounted 64.8%
and 33.2% of among group variability, explaining 98% of total group variability. A
dendrogram based on morphometric and landmark distance data shows the populations of
both the species constructed one cluster and further divided into two distinct sub-clusters.
M. cuchia collected from Mymensingh and from Dinajpur constructed one sub-cluster
and O. bengalense collected from Satkhira and from Bagerhat constructed another sub-
cluster based on the Distance of squared Euclidean dissimilarity. A correct classification
of individuals into their original population from leave-one-out-classification varied
between 93.3% and 94.1% by discriminant analysis and 95.9% of individuals could be
classified in their correct priori grouping. Morphological characterization could be used
effectively to know the population structure and taxonomic status. Both eels have high
commercial value with domestic and overseas demand and their biodiversity should be
conserved and should be brought under aquaculture to save them from extinction.
CHAPTER I
INTRODUCTION
INTRODUCTION
1.1. Importance of Fisheries in Bangladesh
Bangladesh is a country of rivers, rivulets and tributaries. These water bodies are abound
in fishery resources. Fisheries sector has been playing a significant role from time of
immemorial in Bangladesh. Around 58% of animal protein is being supplied by the
commercially important fisheries organisms to the people of Bangladesh (DoF 2010).
Bangladesh is one of the richest countries of the world considering the availability of
fisheries resources but annual fish production is still a lesser amount than the demand of
the people. Bangladesh earns second highest foreign currency from fisheries sector by
exporting fisheries products. Also considering product sources, fisheries sector is found
to be the highest export earning sources because of fisheries products are completely of
native sources. According to Department of Fisheries (DoF 2010), fisheries sector
contributed 3.74% to GDP and 22.23% of total agricultural production of Bangladesh.
Besides, fisheries sector contributes 2.70% to the country’s total export earnings in 2009-
10 fiscal years.
Fisheries and aquaculture play a major role in nutrition, employment and foreign
exchange earnings with about 12 million people are associated with the fisheries sector,
of which 1.4 million people rely exclusively on fisheries related activities (DoF 2010).
The country's main exportable product is frozen shrimp/prawn, live fish, frozen fish, dry
fish, salted and dehydrated fish, turtles, tortoises, crab, eels, shark and other fishes (DOF
2010).
The mud eel, Monopterus cuchia and the swamp eel, Ophisternon bengalense are the
recent export item in Bangladesh and play a vital role for earning foreign currencies.
Both species are locally known as cuchia and are the important species considering their
medicinal value as because their blood contain highest amount of hemoglobin.
1.2. Description of two eels and distribution
Classification of M. cuchia [ Kingdom Animalia
Phylum Chordata
Sub-phylum Vertebrata
Class Osteichthyes
Subclass Actinopterygii
Infraclass Acanthopterygii
Superorder Teleostei
Order Synbranchiformes
Sub-order Synbranchoidei
Family Synbranchidae
Genus Monopterus
Species Monopterus cuchia
(Hamilton of 1822)
The mud eel, Monopterus cuchia is a freshwater air breathing fish, locally known as
cuchia (Fig.1.1). They are capable of dispersal overland, and able to survive for long
periods out of water. M.cuchia is commonly found in the freshwater of Bangladesh,
Pakistan, Northern and Northeastern India and Nepal (Jingran and Talwar 1991).
Fig .1.1. Photograph of Mud eel, Monopterus cuchia (Hamilton of 1822)
They have high fecundity, and are protogynous hermaphrodite. Once, indigenous mud eel
- M. cuchia was abundant throughout Bangladesh. They were available in plenty in mud
holes in shallow “beels” and “boro” paddy field particularly in greater Sylhet,
Mymensingh and Tangail Districts (Rahman 2005). Now-a-days this fish is hardly found
in the open water system due to over exploitation and various ecological changes in its
natural habitat. Therefore, IUCN-Bangladesh (2000) enlisted M. cuchia as a vulnerable
species in Bangladesh. The fisheries resources are under severe threat due to sediment in
the downstream of the river system which reduces the rate of water flow and changing
aquatic ecosystems, human interventions through construction of flood control
embankments, drainage structures and sluice gates, conversion of inundated land to
cropland and indiscriminate destructive fishing practices and use of pesticides (Hossain et
al. 2009). Pollution from domestic, industrial and agrochemicals wastes and run off have
resulted in threat of a considerable amount of aquatic biota in all stretches in the open
water system.
Classification of O. bengalense
Kingdom Animalia
Phylum Chordata
Sub-phylum Vertebrata
Class Osteichthyes
Subclass Actinopterygii
Infraclass Acanthopterygii
Superorder Teleostei
Order Synbranchiformes
Sub order Synbranchoidei
Family Synbranchidae
Genus Ophisternon
Species Ophisternon bengalense
(McClelland of 1844)
The swamp eel also known as Bengal eel, Ophisternon bengalense is a freshwater,
demersal and brackish water eel (Fig. 1.2). It is distributed in India, Sri Lanka, Indonesia,
Philippines and New Guinea. Adults inhabit both fresh and brackish waters of rivers and
swamps or near the river mouth. They found mainly in thick vegetation of muddy, still
water bodies, such as lagoons, swamps, canals and rice fields. This fish species prefers
estuarine or tidal areas and they also live in soft bottom sediments in quiet, well vegetated
backwaters of brackish estuaries and nearby swamps, usually in burrows.
Fig. 1.2. Photograph of swamp eel, Ophisternon bengalens (McClelland of 1844)
The male guards and builds nest or burrow. This species moult their body sometimes.
Their sexing pattern is mostly unknown. Their skin is so much thin and when they moult,
they become very aggressive. Because of its taste O. bengalense is a fish of high demand
to the tribal people of Bangladesh and people of China, Hong Kong, Thailand, Vietnam,
Malaysia, Japan and Indonesia.
1.3. Global importance
Eels are considered as a nutritious and tasty fish species and it is also a valued medicinal
species in oriental region. Raising eels is presumed a low-cost enterprise to farmers. It is
easy to do and achieves more profit than some other small size fish-culture activities
(IIRR et al. 2001; Lu et al. 2005). In recent years, the rice field eel culture has been
increased strongly in some areas of Vietnam. They are consumed mainly by domestic
market and some consumed by export markets.
Globally eel production was expected to grow by thrice between 1985 and 1992 which
representing an increase of about 58% (ADCP 1995). World aquaculture production of
freshwater eels has increased over the past decade and is currently around 2,33,000
MT/year which valued at over US$975 million (FAO 2005; FAO/UN 2005). A
significant commercial eel fishery exists in various countries like Australia, Thailand,
Malaysia, Japan, Korea, USA, China, Italy, Greece, Egypt, Singapore, Cambodia and
Taiwan (ADCP 1995; Hicks and McCaughan 1997; August and Hicks 2006) consisting a
great available export market (Ishak 1994; Moriarty and Dekker 1997; Jessop 2000). The
rapid expansion of eel farming in Japan since the middle of the 19th century aroused
considerable interest in intensive farming of eel and eel culture enterprises have
developed in a number of countries in Europe, especially Italy, Germany, Netherlands
and France. In Asia, Taiwan has become a major exporter of cultured eels to Japan and
European markets.
1.4. Importance in Bangladesh context
Shrimp, Bangladesh’s main aquatic export item facing grave environmental, socio-
political and socio-economic consequences have resulted in the wake of its expansion
which jeopardized the livelihoods of millions, particularly the most vulnerable women
and children (Mazid 2002). Concurrently, crab is gaining an important position of
immense prospects. However, eels, a recent export item, though, have not yet been given
any attention of its culture and collection could be considered as an alternative option for
poor peoples. Collection from the wild to meet growing export demand and lack of
aquaculture of this species could be the major concern for biodiversity loss in
Bangladesh. However, considering the increasing demand in the international markets
(Usui 1991; VAC 1999; FAO 2005) eel fishery has been gaining popularity among the
coastal community of greater Khulna and Chittagong regions as well as greater
Mymenshing, Shylet and Comilla region. Five species of eel, Monopterus cuchia,
Anguilla bengalensis, Ophisternon bengalense, Pisodonophis boro and Pisodonophis
cancrivorus (Chowdhury et al. 1980; FRSS 1984 and BOBP 1985) are available in
Bangladesh, in which, M. cuchia, P. boro and O. bengalense are presently being exported
to Japan, Korea, Hong Kong, Thailand, China and Taiwan from Bangladesh. Mud eel
collecting from wild is exported in a large quantity to China and other Asian countries
and no fry production and culture is practiced yet. On the other hand, plenty of works on
reproductive physiology, neuroendocrine mechanism of reproduction, fry production and
aquaculture of its close relative from the same genus (swamp eel, M. albus) have already
been done in many countries and intensive aquaculture of eels have been practiced for its
high market value (Chen and Fernald 2008; Fu and Zhengfeng 2009; Khanh and Ngan
2010; Wang 2010; Jun 2010; Chu et al. 2011).
Cuchia is an important fish for the livelihoods of Adivasi people in terms of both for
home consumption and trade. However, the availability of the eel has been drastically
reduced over the years. Several factors contributed to this, while the main two factors are
the destruction of natural habitat and over harvesting. The natural habitats of cuchia has
been destructed by variety of ways like horizontal expansion of agriculture and
aquaculture, destructive hunting methods, use of chemicals, fertilizer and pesticide,
infrastructure development etc. On the other hand, harvesting of cuchia has been
increased with the increase of population, which is further influenced by the international
demand and trade of cuchia. Many of poor Adivasi people harvest and sell cuchia as a
full-time or part-time profession.
In this background, increase in production of cuchia through restoring and protecting
natural habitats on sustainable harvesting may be a good option improving livelihoods of
Adivasi people. In addition, most of the mainstream people of Bangladesh do not eat
cuchia and considered cuchia production as an advantage only to the Adivasi people.
Seeing the potential, a few donor has funded project to increase production of cuchia in
small suitable private owned resources involving poor Adivasi people along with owners
in culturing cuchia and improvement of habitats. However, lack of knowledge and
information on cuchia culture technique in such natural environments was found to be an
important constrain.
Since there is very little culture for freshwater eels, it is necessary to develop a scientific
eel culture system. Advanced aquaculture is not possible without proper understanding of
the various biological factors of fishes such as morphological study, food and feeding
habit, hematology, reproductive biology and optimum growth and water quality
parameters which are responsible directly for the production of biomass in a water body.
1.5. Aquaculture potential
Aquaculture is a part of art and part of science. As time goes on, we understand more
about where this division lies and the science of aquaculture continues to mature
enhancing our understanding of the complexities that ensure profitable production of a
given species. Freshwater eels are generally available in open water resources such as
rivers, beels (relatively large waterbodies with static water in the Ganga-Brahmaputra
flood plains of Bangladesh), haors (wetlands in the northeastern part of Bangladesh
which are a bowl or saucer shaped shallow depressions), baors (oxbow lakes, found
mostly in moribund deltas as in northeastern Bangladesh), canals, floodplains and
estuaries. Comparatively shallow and small ponds, ditches, tanks or cisterns also could be
utilized to culture freshwater eels as they tolerate various adverse conditions such as low
oxygen levels, high temperature and shallow water. However, the eel aquaculture
industry in Bangladesh is completely absent, only capture based fishery practice are
performed. Both freshwater and saltwater eels of Bangladesh could be grown for
international market. Hence, Bangladesh has great opportunity to develop eel farming
industry and to enter European and Asian markets, if proper attempt could be taken. Although some laboratory-scale progress have been made in maturing and fertilizing the
eggs of some species of eels, it has not yet been studied in response to the whole
morphological characterization of eel.
1.6. Justification of the study
Study of the morphological characters is a prerequisite for domestication and culture of
any animals either aquatic or territorial. Now a days, two cuchia are only caught from
wild to meet up the increasing demand in the international market. As a result, the
biodiversity of both of the species is already in danger. It is essential to develop
sustainable aquaculture technology to save the species and take the advantage of export
market. It is also necessary to develop the breeding technologies for both for the species
for mass seed production for the sustainable eel aquaculture. The initiatives for the
development of these technologies are in infancy in Bangladesh. The urgent need is
detailed phenotypical study for both the species which is essential for domestication and
development of breeding technologies.
To better understand and document morphological variation in two eels M. cuchia and O.
bengalense, their head and body shape and color pattern, their whole physical
characteristics and comparison between them is essential. Populations in close
geographic proximity may represent separate introductions of genetically distinct forms
thus has significant management implications. Few attempts have been taken to study of
larval rearing and reproductive biology of eels in Bangladesh but to our knowledge,
comparison of their morphological characteristics so far is not studied. Therefore, the
present study was conducted to characterize and compare the two eels M. cuchia and O.
bengalense.
1.7. Objectives:
In this experiment, the following objectives have been outlined:
• To characterize phenotype of two eel species- M. cuchia and O.
Bengalense;
• To study the physical characteristics of body;
• To determine the relationship among morphometric and meristic characteristics;
and
• Comparison the two species with their physical characteristics.
CHAPTER II
REVIEW OF LITERATURE
REVIEW OF LITERATURE
The purpose of this chapter is to review previous studies, opinions and observations of
experts which are related to the present study. Comprehensive and systematic reviews of
previous research works provide a strong base for carrying out any scientific research. A
reference to the previous work provides guidelines for not only to frame study
hypothesis, methodology to be adopted, future areas of research to be covered but also
substantiate or repudiate research out come with possible reason. Few published works
related to morphological characterization between Monopterus cuchia and Ophisternon
bengalense and some related literature on different fish have been reviewed and
presented followings:
Darlina et al. (2011) investigated Mackerel (Scombridae; Rastrelliger) are small
commercially important pelagic fish found in tropical regions. They serve as a cheap
source of animal protein and are commonly used as live bait. By using a truss
morphometric protocol and RAPD analysis, there examined morphological and genetic
variation among 77 individual mackerel that were caught using long lines and gillnets at
11 locations along the west coast of Peninsular Malaysia. Nineteen morphometric traits
were evaluated and genetic information was estimated using five 10-base RAPD random
primers. Morphometric discriminant function analysis revealed a single group of
Rastrelliger brachysoma can be found along the west coast of Peninsular Malaysia. They
found that the head-related characters and those from the anterior part of the body of
Rastrelliger spp significantly contribute to stock assessment of this population. RAPD
analysis showed a trend similar to that of the morphometric analysis, suggesting a genetic
component to the observed phenotypic differentiation. These data will be useful for
developing conservation strategies for these species.
Mekkawy et al. (2011) reported the morphometric and meristic characteristics of
Cephalopholis argus, Cephalopholis miniata and Variola louti. The type of allometry of
the morphometric traditional as well as truss characters in terms of size and shape were
determined. The morphometric indices exhibited a great variability in their behavior
among the three Epinepheline species studied and in turn different mode of growth of
such species. However the only indices to be size-free are PRVFL/SL, DEVOFL/SL,
DEDCFL/SL VDOL/HL, VEAOFL/HL, AEVCFL/HL and AEDCFL/HL for the three
Epinepheline species considered. The clustering of the allometric growth was considered
as a taxonomic tool in fishes. The inter and intra-specific relationship between the three
Epinepheline species were also evaluated on further patterns of size and shape using
standard DFA and cluster analysis.
Roesma and Santoso (2011) reported that morphological divergences among three
sympatric populations of Silver Shark minnow (Cyprinidae: Osteochilus hasseltii) in
West Sumatra. Silver shark minnow (Osteochilus hasseltii) named by local people as
Asang is one of potential Cyprinid fish species found in several different ecosystems in
West Sumatra. The differences of habitat types and another ecological factor among
populations may have significant influences on variation and differentiation of
morphological characters of this species. In order to elucidate the pattern of
morphological divergence, meristic and morphometric characters of O. hasselti in
Singkarak and Dibawah Lake and adjoining river were compared. Phenogram based on
cluster analysis showed specific morphological divergence among populations. There
were 23 characters significantly different among all compared populations, the highest
degree of differentiation was found between Singkarak and Dibawah Lake population (22
characters significantly different) and the most similar population were Singkarak Lake
and Ombilin an outlet river of lake (only six characters significantly different).
Hossain et al. (2010) reported Landmark-based morphometric and meristic variations of
the endangered carp, kalibaus Labeo calbasu, from stocks of two isolated rivers, the
Jamuna and Halda, and a hatchery Landmark-based morphometric were examined to
evaluate the population status of the endangered carp, kalibaus L. calbasu, collected from
2 isolated rivers (the Jamuna and Halda) and a hatchery. Morphometric characters along
with truss network measurements and meristic counts were applied. Significant
differences were observed in four (maximum body height, pre-orbital length, peduncle
length, and maxillary barbell length) of 12 morphometric measurements, two (pectoral
fin rays and scales above the lateral line) of 9 meristic counts, and four (8 to 9, 3 to 10, 2
to 10, and 1 to 11) of 22 truss network measurements among the stocks. The dendrogram
based on morphometric and truss distance data placed the Jamuna and hatchery in 1
cluster and the Halda in another cluster, and the distance between the Halda and hatchery
populations was the highest.
Erguden et al. (2009) reported that morphometric and meristic analyses of chub mackerel
Scomber japonicus were used to discriminate stocks throughout the Black, Marmara,
Aegean, and northeastern Mediterranean Seas. Morphometric and Meristic analyses
showed a similar pattern of differentiation between S. japonicus stocks and revealed a
clear discreteness of two groups, northeastern Mediterranean (Antalya Bay–Iskenderun
Bay) and the northern group, including the Aegean, Marmara, and Black Seas. Hossain et al. (2009) describe the morphometric, meristic characteristics and threatening
factors for the critically endangered species Puntius sarana (Hamilton 1822) in the lower
part of Ganges River, northwestern Bangladesh. A total of 87 specimens ranging from
9.30-21.70 mm TL (total length) and 10.05-189.25 g body weight (BW) were used for the
studies of the morphometric and meristic characteristics. The necessary data and
information were collected through the interview or survey on >120 fishers and >80 fish
farmers from March 2006 to December 2007. The results indicated that the populations
are declining due to over-exploitation, pollution and environmental degradation, spread
of disease, uncontrolled introduction of exotic fish, and lack of proper management. This
study also suggested the measures for the conservation of the remnant isolated population
of P. sarana in the Ganges river and nearby areas.
Neves et al. (2009) carried out experiment on to morphologically characterization and
classified the stages of gonad development in different Nile tilapia strains (Oreochromis
niloticus).
Pollar et al. (2007) stated that the population structure of the Tor tambroides was
investigated with morphometric data (i.e. morphometric measurement and truss
measurement). A morphometric analysis was conducted to compare specimens from
three waterfalls: Sunanta, Nan Chong Fa and Wang Muang waterfalls at Khao Nan
National Park, Nakhon Si Thammarat and Southern Thailand. The results of stepwise
discriminant analysis on seven morphometric variables and 21 truss variables per
individual were the same as from a neural network. Fish from three waterfalls were
separated into three groups based on their morphometric measurements. The
morphometric data shows that the nerual network model performed better than the
stepwise discriminant analysis.
Urra et al (2007) analyzed morphometric differentiate Adelomelon ancilla and
Odontocymbiola magellanica (Caenograstropoda: Volutidae) of southern Chile. The
volutid snails Adelomelon ancilla and Odontocymbiola magellanica are of economic
importance to the fishery of Chile’s southern zone. These species were direct developers,
which made them very sensitive to localized catches but there were no fishery regulations
to control their catches. Although these sympatric species might be distinguished by their
radular morphology, their external characteristics (used in field recognition) were so
similar that they wee confusedly lumped under the common name of “piquilhue” snail
and registered as A. ancilla in the fisheries national statistics. With the aim of
identifying external population characters which could facilitate discrimination between
taxa, common samples of piquilhue snails were taken and separated into 330 A. ancilla
and 54 O. magellanica using identification guides. The radular morphology, and shell
and body characteristics of these 2 species were evaluated through traditional and
landmark-based geometric morphometric methods. The results revealed that the species
could not be distinguished by meristic traits (number of whorls and columella folds) or by
the thickness or weight of their shells, but they did exhibit significant differences in shell
shape and body weight. Adelomelon ancilla had a fusiform shell shape (a small aperture
and a high-spired shell) that accommodated a smaller body mass than that of O.
magellanica, which had a globose shape (a larger aperture and a low-spired shell). The
external differences found by traditional and geometric analyses are sufficient to
discriminate between the 2 species, which would be useful in establishing proper
fisheries statistics and adequate management strategies.
Turan et al. (2006) studied the genetic and morphological variation of Pomatomus
saltatrix were studied based on morphometric and meristic analyses of samples collected
throughout the Black Seas, Marmara, Aegean and eastern Mediterranean Seas. In
discriminant function analysis, plotting first and second discriminant functions explained
61% and 77% of the between-group variation for morphometric and meristic analyses
respectively, and indicated existence of three morphologically differentiated groups of P.
saltatrix.
Turan (2004) investigated that Morphologic differentiation among stocks of
Mediterranean horse mackerel, Trachurus mediterraneus, throughout the Black,
Marmara, Aegean and Eastern Mediterranean Seas, was investigated using morphometric
and meristic characters. Discriminant function analysis of both morphometric and
meristic characters suggested that there is restricted migration of mackerel among the
adjacent seas. Overlapping of four Black sea samples on the discriminant space in
morphometric and meristic characters suggested that there is one self-recruiting
population in the area. The Marmara sea samples were the most isolated samples from all
others for both morphometric and meristic characters, which may indicate existence of a
distinguishable mackerel stock in the area. The sample from the Aegean Sea was grouped
with one geographically close Mediterranean sample based on morphometrics and
separated from all other Mediterranean samples based on meristic characters, suggesting
some degree of intermingling between these areas. Examination of the contribution of
each morphometric variable to canonical functions indicated that differences among
samples seemed to be associated with the anterior part of the body. In meristic analyses,
highest contributions to canonical functions were associated with the number of gill
rakers and pectoral fin rays.
Turan and Erguden (2004) worked with Liza abu stocks from the Orontes, Euphrates and
Tigris rivers to know the genetic and morphometric structure. Simultaneously, allozyme
electrophoresis for genetic comparison and the truss network system for morphometric
comparison were applied to the same sample set. They observed highly significant
morphological differences between the 3 L. abu stocks. In discriminant function analyses,
plotting discriminant functions revealed high isolation of the 3 stocks and the Tigris stock
was very isolated from the other two stocks. The pattern of phenotypic discreteness
suggests a direct relationship between the extent of phenotypic divergence and
geographic separation. A 5 enzyme system (ICD, PGM, ME, MDH and G3PDH)
composed of 6 loci was used to determine genetic comparison. However, genetic data do
not support the detected morphometric variations. They concluded that major limitation
of morphological characters at the intra-specific level is that phenotypic variation is not
directly under genetic control but is subjected to environmental modification.
Turan et al. (2004) investigated the status of populations of anchovies in Turkish
terrestrial waters was preliminarily investigated using morphometric characters with the
truss network system. Samples were taken from the main fishing areas of each sea,
comprising the central (Sinop) and eastern (Trabzon) Black Sea, the Aegean Sea (Uzmir)
and the eastern Mediterranean (Uskenderun). Plotting discriminant functions 1 and 2,
explaining 93% of between-group variability, revealed a high degree of dissimilarity
among the anchovy samples, indicating that the anchovies in each sea represent different
aggregations. The overall random assignment of individuals into their original group was
high (80%). Pairwise comparisons using multivariate analysis of variance (MANOVA)
showed highly significant differences between all the samples (P<0.001). Univariate
analysis of variance (ANOVA) revealed significant differences with varying degrees
between the means of the 4 samples for 16 out of 25 standardized morphometric
measurements. Principal components analysis (PCA) indicated that the observed
differences were mainly from the measurements taken from the head.
Doherty and McCarthy (2004) illustrated the monomorphic character of the two
populations despite differences in growth and size between the ‘stunted’, slower-growing
Lough Eske fish and the ‘normal’, faster -growing Lough Mask fish. The results are
discussed in the context of other systems where sympatric morphs have been described.
Differences in body size and growth rate appear to reflect the trophic status and the
productivity of the two lakes. The results confirmed earlier findings, which were based on
dietary analysis and analysis of metazoan parasites of both Irish populations of Arctic
charr.
For better understanding of phylogenetic diversity and evolution of PGH alpha in fish,
Han-Yu San and Yu-Yuh Lin (2002) have cloned cDNAs for PGH alpha subunits from
swamp eels, Monopterus albus and Ophisternon bengalense, two members of the Order
Synbranchiformes, Suborder Synbranchoidei, Family Synbranchidae.
Narejo et al. (2001) reported that variations in the haematological parameters of the
freshwater mud eel, Monopterus cuchia (Hamilton) with respect to sex and season.
Nakamura (2001) stated that Meristic and morphometric characters of local populations
of fluvial Japanese charr, Salvelinus leucomaenis, which had been isolated above dams
and a waterfall, were compared between river systems (Naka and Tone rivers, central
Japan) and among the tributaries of the Naka River (Ashinagasawa, Akasawa,
Ushirosawa and Moto-okashirasawa streams). Between the river systems, there was a
significant difference in the mean number of dorsal fin rays, pyloric caeca, white spots
under the lateral line and the proportion of the diameter of the white spots to the diameter
of the pupil, respectively. On the other hand, among the tributaries within a river system,
a significant difference was occurred in the mean number of anal fin rays, pored scales on
the lateral line, gill rackers, vertebrae, pyloric caeca, white spots under the lateral line,
white spots on the surface of the gill covers and the proportion of the diameter of the
white spots to the diameter of the pupil, respectively. A dendrogram based on data of the
meristic and morphometric characters showed that the population of the Tone River was
included within the variation detected among the tributary populations of the Naka River.
Meristic and morphometric characters of Japanese charr varied not only between river
systems but also among tributaries within a river system.
Turan and Basusta (2000) evaluated the degree of differentiation among populations of
twaite shad, Alosa fallax nilotica, in Turkish territorial waters with the truss
morphometric system using Discriminant Function (DFA) and Principal Component
Analyses (PCA). Approximately 40 individuals were collected from each sea to represent
regions. In DFA, the proportion of correctly classified Eastern Mediterranean sea sample
to their original group was highest (90%) with a high overall random assignment of
individuals into their original population (78%). Plotting discriminant function 1 (DF1)
and discriminant function 2 (DF2) explained 100% of total between group variability and
clearly discriminated Eastern Mediterranean sea sample from the Baltic and Aegean sea
samples, which were over plotted. This finding was also supported in multivariate
analysis of variance. PCA revealed that the observed differences were mainly from
posterior morphometric measurements of the fish. The patterns of morphological
differentiation suggested that there is limited exchange of individuals among areas to
homogenize populations phenotypically from the Black and Aegean seas to Eastern
Mediterranean sea.
Turan (1999) identified intraspecific units or stocks of a species with unique
morphological characters enable a better management of these subunits of species and
ensure perpetuations of the resources. Multivariate morphometry has been commonly
used to investigate the discreteness and interrelationships of stocks within a species.
Different types of body measurements have been traditionally used to charecterise stocks.
As an alternative, a new system of morphometric measurements called The Truss
Network System has been increasingly used for stock identification. In this review a
computer-originated approach to the collection and analysis of morphometric
characteristics of stocks is described.
Hunt (1992) reported the relationships between otolith dimensions and fish size for six
demersal and two pelagic species. Otolith morphometric observations included length
for all species examined and weight ,width, volume, cross - sectional area and
location of the focal point for the selected species.
Swain et al. (1991) used the truss system in the identification of hatchery and wild
populations of Coho salmon (Oncorhynchus kisutch). They found significant
morphometric variation. They commented that the variation was attributed to an effect of
the rearing environment rather than genetic differences between the hatchery or wild
stocks.
Henault M. and Fortin R. (1989) compared the meristic and morphometric phenotypes of
the spring-spawning stock of ciscoes (Coregonus artedii) from lac des Ecorces with those
of fall-spawning stocks from the same drainage basin. Meristic and morphometric
phenotypes of the spring-spawning stock of ciscoes (Coregonus artedii) from lac des
Ecorces were compared with those of fall-spawning stocks from the same drainage basin.
The spring spawners show almost complete non overlap in gill rakers compared with fall
spawners (averages of 42.7 and 50.5 respectively). This large gap could indicate
genotypic differences between these stocks. Spring spawners also show smaller numbers
of lateral line scales and of dorsal and anal fin rays, which might be related to higher
incubation temperatures. Based on the comparison of conventional and truss network
measures, discriminant analyses performed separately on males and females showed that
the head and cephalic structures are smaller in spring ciscoes; their thoracic region is also
longer and their caudal peduncle narrower and shorter. A principal components analysis
showed that the few fall-spawning ciscoes captured in lac des Ecorces do not differ from
the fall spawners occurring upriver: the spring-spawning population would thus be
allopatric.
Vascularization of the pectoral fin and capacity of larval respiratory organs were also
studied by Munshi et al. (1989) for Monopterus cuchia. Observations on breeding habits
and larval development were also provided for the Asian synbranchids Monopterus albus
(Wu and Liu 1942), M. cuchia (Banerji et al. 1981), and Ophisternon bengalense
(Rangarajan and Jacob 1960). [[[[
Ojeda (1986) reported the morphological characterization of the alimentary tract of
Antarctic fishes and its relation to feeding habits. Morphological and morphometric
characteristics of the alimentary tract in 22 species of carnivorous antarctic fishes were
studied. It is shown that all of these species have similar, well-developed Y-shaped
stomachs with generally thick (0.5–1.0 mm) walls. The relative stomach lengths are also
similar, ranging from 9.8 to 22.2% of body length. Relative intestine lengths, a
characteristic frequently used as an indicator of the kind of food eaten by a species, are
also remarkably similar among most species (31 to 67%). Notothenia gibberifrons, a
conspicuous benthos feeder, has a significantly longer intestine (91%), probably as an
adaptation to the quantity of undigestible material (mud) incorporated with its faunal
prey. These values fit within or below the limits (60–150$) of relative intestine length
described in the literature for carnivorous fishes. The number of pyloric caecae is in
general relatively low and fairly constant in each species. It is concluded that the
morphological features studied could represent similar adaptations of these antarctic
fishes to a similar carnivorous diet.
The biometric analysis, including meristic and morphometric characters, has been
adopted by many authors to identify and relate different fish races and/or populations
(Khalil et al. 1984; Mekkawy 1995; Mekkawy et al. 2002, Turan 2004 and Ali and
McNoon 2010). This trend in biometric analysis reflects its validity in stock identification
in different fisheries of the world.
Few studies on morphological variation within different fish species have been reported
(Prakash and Verma 1982; Hoque and Rahman 1985; Kohinoor et al.1995; Azadi and
Naser 1996). Sex related morphological variation have also been reported by Islam et al.
1983. Unfortunately no published information on morphometric studies of freshwater
mud eels is available.
The morphological variations have been used as a basic tool in separating population of
species (Seymour 1959; Anthony and Bayer 1968). For the proper identification of fish, it
is essential to study its morphometric characters. The review of literature indicates that
there are two types of freshwater mud eels Monopterus cuchia and Monopterus albus and
three species of baim Mastacembelus armatus, Mastacembelus pancalus, Mastacembelus
aculeatus of similar colour, shape, size and characters are available in different water
bodies of Bangladesh (Rahman 1989; Jhingran and Talwar 1991). It is therefore essential
to determine whether the fish samples of Monopterus cuchia and Ophisternon bengalense
handled during the course of present investigation belonged to a single homogenous
population or not.
CHAPTER III
MATERIALS AND METHOD
2
2
2 2
MATERIALS AND METHODS 3.1. Collection of sample Monopterus cuchia sample were collected from two places of Bangladesh, Dinajpur and
Mymensingh and Ophisternon bengalense were collected from two places, Satkhira and
Bagerhat (Fig. 3.1).
Fig. 3.1. Map of Bangladesh showing sampling sites of M. cuchia & O. bengalense.
3.2. Rearing of sample Two fish species (total thirty two M. cuchia and seventeen O. bengalense from four
areas) were reared in two tanks at the Mini Hatchery under the Faculty of Fisheries,
Bangladesh Agricultural University and Mymensingh. The fishes were reared with
intensive care, maintaining appropriate water quality and fed with live earthworm and
tubifex twice a day. Small parts of bamboos were in place for their shelter.
3.3. Measurement of morphometric and meristic characters
3.3.1. Morphometric characters Twenty six morphometric characters and body weights of the fish were measured with an
accuracy of 0.05 mm and 1.0 g, respectively (Table 3.1.) A total of nine meristic
characters (Table 3.2) were analyzed. Six landmarks determining eight distances were
measured on the fish body (Fig. 3.2).
Table 3.1. The morphometric characters measured
Characters Description
1. Total length (TL)
2. Pre dorsal length (PDL)
3. Post dorsal length (PoDL)
4. Pre anal length (PAL)
5. Post anal length (PoAL)
6. Length of lateral line (LAL)
7. Head length (HL)
8. Snout length (SnL)
Distance from the tip of the snout to the
longest caudal fin ray
Distance from the snout tip to the anterior
base of the dorsal fin
Distance from anterior base of the dorsal fin
to last part of the caudal fin
Distance from the tip of the snout to the anal
base
Distance from the anal base to the last part of
the anal fin
Distance from the first base to the last base of
lateral line
Distance from the tip of the snout to the
posterior margin of the opercula
Distance from tip of mouth to nostril
9. Upper jaw length (UJL)
10. Lower jaw length (LJL)
11. Mouth gape (MG)
12. Eye diameter (ED)
13. Head depth (HD)
14. Head width (HW)
15. Pre orbital length (POL)
16. Post orbital length (PoOrL)
17. Greatest body depth (GBD)
18. Least body depth (LBD)
19. Greatest width of body
(GWB)
20. Highest body diameter
(HBD)
21. Width of body at vent
(WBV)
22. Depth of body at vent
(DBV)
23. Distance between vent and
commencement of dorsal fin
(DBCB)
24. Intestine length (IL)
25. Fat length (FL)
26. Length beside lateral line
(LBLL)
Length of upper jaw
Length of lower jaw
Length of mouth gape
Diameter of eye
Depth of head
Width of head
Distance from tip of mouth to anterior base of
eye
Distance from posterior base of eye to last
hard part of head
Greatest body depth of the body
Least body depth of the body
Width of body at greatest part
Diameter of the highest body part
At vent base width of the upper part of the
body
Depth of body at vent base
Distance between at vent base to dorsal fin
base
Length of intestine
Length of fatlike structure which attached
with the intestine
Length beside lateral line
TL LLL LLLL
LLL LLLL
LLL
LL
22
2
2222
222 22
WLV
GWL
The fat length (fat like structure with small blackish dot shown attached with intestine)
was measured only in case of Ophisternon bengalense, which only present in this species.
In case of Monopterus cuchia four lines were present beside lateral lines which were
measured. Figure 3.2 shows the morphometric measurement. The measurement were
done in the way in both species.
Fig. 3.2. Morphometric measurements of cuchia.
3.3.2.Meristic characters
Table 3.2. The meristic characters of eels
Characters Description
1. Body line The number of line present in the body
2. Line below head The number of line below head
3. Teeth The number of teeth at both in the upper and lower jaw
4. Gill raker The number of gill rakers
Five meristic characters were analyzed and measured (Table 3.2). The characters were-
No. of line in body, No. of line below head, No. of teeth in both the upper jaw and lower
jaw and No. of gill rakers. No. of gill raker were same for both species, but in case of
Ophisternon bengalense teeth were very small so it was not possible to count the teeth for
this species.
3.4. Land mark distances of the species
The truss network system described for fish body morphometrics (Hossain et al. 2010)
was used to construct a network on fish body, 6 landmarks determining 8 distances were
produced and measured as illustrated in Fig. 3.3. Each landmark was obtained by placing
the fish on a graph paper and then the landmark points were detected with colored
pointers. Finally the distances on the graph paper were measured using vernier calipers.
Fig. 3.3. Six landmarks determining 8 distances on eel body.
3.5. Dissection of the species: After measurement of morphometric, meristic and landmark distances, the fish were
dissected using scissors and tweezers. Intestine of the fish were cleaned with tap water
and were measured. The sex pattern was observed, head was dissected and the gill rakers
were observed and both upper jaw and lower jaw were cut and the teeth were counted.
3.6. Statistical analyses Sexes were determined by macroscopic examination of the respective gonads and this
subset was used to test hypothesis of no sexual dimorphism in morphometric, landmark
distance and meristic characters of both the species. Sexual variation was analyzed using
independent sample t-tests.
A multivariate discriminant analysis was used for morphometric data to identify the
combination of variables that best separate both the species. Prior to the analysis, size
effects from the data set were eliminated. Variations were attributed to body shape
differences, and not to the relative size of the fish. In the present study, there were
significant linear correlations among all measured characters and the total length of the
fish. Therefore, it was necessary to remove size-dependent variation for all the characters.
1
2
3 4
5
6
An allometric formula given by Elliott et al. (1995) with slight modification was used to
remove the size effect from the data set.
Madj = M (Ls / Lo) b
Where M: Original measurement, Madj: Size adjusted measurement, Lo: Total length of
fish, and Ls: Overall mean of total length for all fish from all samples. Parameter b was
estimated for each character from the observed data as the slope of the regression of log
M on log Lo, using all fish in all groups. The efficiency of size adjustment
transformations was assessed by testing the significance of the correlation between
transformed variable and total length.
Efficiency of the allometric formula in removing size effect from the data was justified
by using correlation between total length and the adjusted morphological, meristic
characters and landmark distances. Total length were excluded first and not transformed
because using this parameter as standard all other parameters were standardized. After
the allometric transformation, the correlation results revealed that all of the meristic
variables studied were free from the influence of size.
The degree of similarity among samples in the overall analysis and relative importance of
each measurement for group separation were assessed by discriminant function analysis
(DFA) with cross validation. Population centroids with 95% confidence ellipses derived
from the DFA were used to visualize relationships among the individuals of groups. A
dendrogram of the populations based on the morphometric and landmark distances data
was drawn by the unweighted pair group (UPGMA) cluster analysis. Univariate analysis
of variance (ANOVA) and independent sample t-test were carried out to test the
significance of morphological differences. Comparison of meristic characters was done
using non parametric Mann-Whitney U test. Resulting DFAs were examined for the
extent of classification between two stocks and between stocks. In addition, a “leave-one-
out cross-validation” was performed on each DFA as a testing procedure. All statistical
analyses were done using SPSS v 11.5.
CHAPTER IV
RESULTS
RESULTS
4.1. Length and body weight of M. cuchia and O. bengalense and their sexing
pattern
Morphometric, truss measurements and meristic characters from thirty two M. cuchia and
seventeen O. bengalense were analyzed in this experiment. Their sex patterns were found
to be heterosexual i.e. male and female in both the species. There were nineteen males
(59.4%) and thirteen females (40.6%) in M. cuchia and five males (29.4%) and twelve
females (70.6%) in O. bengalense (Table 4.1). The average length and weight of M.
cuchia were 62.74±6.84 cm and 547.03±271.48 g respectively. On the other hand the
average length and weight of O. bengalense were 53.12±5.27 cm and 161.76±33.21 g
respectively. The sex and location wise length and weight of M. cuchia and O.
bengalense are presented in the Table 4.1. Table 4.1. Length and weight of M. cuchia and O. bengalense and their sexing pattern (SD
= standard deviation, n = number of fish) and the range
Species Sex Location of
samples
n Mean total
length ± SD
(cm)
Mean weight ±
SD (g)
M. cuchia F 1 4 70.15±4.45
(66-74)
825±28.87
(800-850)
M 13 67.9±2.14
(62-71)
771.54±118.99
(500-900)
F 2 9 58.82±2.69
(52-61)
281.11±68.23
(150-300)
M 6 55.5±4.07
(52-63)
274.17±74.39
(215-400)
O. bengalense
F
3
6
53.02±2.60
(48-55)
158.33±20.41
(150-200)
M 2 100±0
(48-48)
47.6±0
(100-100)
F
4 6
53.72±5.96
(46-63)
175±27.39
(150-200)
M 3 55.83±8.60
(48-63)
183.33±28.89
(150-200)
M: Male; F: Female; 1. Mymensingh 2. Dinajpur 3. Satkhira and 4. Bagerhat
4.2. Physical characteristics
Body description
The body is cylindrically elongated. The body colour of M. cuchia is brownish dark with
numerous small black and yellowish blotches. Body is triangular in shaped. The skin is
very thick and rough looking. The dorsal part of body is dark brownish and ventral part is
yellow brownish. All over the body, numerous black blotches are present (Fig. 4.1).
Fig. 4.1. Body colour (ventral view-left and dorsal view-right) of M. cuchia.
The body of O. bengalense is rounded and elongated. The body colour is lightly red
brownish with very little minute light blackish spot all over the body. The whole body is
more or less smooth. The dorsal part of the body is somewhat dark reddish brown. The
ventral part is whitish red. The skin of body is somewhat transparent with light zigzag
starting slightly far of chest (approximately 5 cm far) the line are more dominant in dead
fish (Fig. 4.2).
Fig. 4.2. Body colour (ventral view-left and dorsal view-right) of O. bengalense.
The head shape of M. cuchia is triangular. Middle part of the head is slightly straight.
Numerous lines and black blotches are also present on the head. Eyes are small and
visible through a translucent layer of skin. Mouth part is blunt shape. Upper jaw is very
long due to large head size (Fig. 4.3).
Fig.4.3. Head shape of M. cuchia.
The head in O. bengalense is short and rounded. Mouth part is sharp. At the upper part of
jaw there are two small barbells. Eyes are protractile and no line is present as M. cuchia.
The middle part of the head is anteriorly rounded. Upper jaw is not long due to short head
size (Fig. 4.4).
Fig. 4.4. Head shape of O. bengalense.
At ventral part of head there are various lines arranged in ‘V’ liked shape. More
than 22-28 lines are arranged here. The lines end near to the lower jaw. In the M. cuchia
two sides of the head look swollen because of respiratory sac (Fig. 4.5).
Fig.4.5. Head shape (ventral side) of M.cuchia.
In the ventral part of O. bengalense there are around 10 lines arranged in crescent shape.
Lines finally end near the lower jaw (Fig. 4.6). The two sides of the head are not swollen.
Fig. 4.6. Head shape (ventral side) O. bengalense.
There are four lines present beside the lateral line in M.cuchia.There is no line present
beside lateral line in O. bengalense (Fig. 4.7)
Fig. 4.7. Lines present beside lateral line in M. cuchia (left) and no line present in O.
bengalense (right).
The last part of the tail of M. cuchia is blunt shaped. The dorsal and anal fin are
rudimentary i.e. they are not dominant. The dorsal fin is originated slightly away from the
dorsal part from the anus (Fig. 4.8).
Fig. 4.8. Tail shape of M. cuchia (left) and O. bengalense (right)
The last part of the tail of O. bengalense is sometwhat a sharp structure. The dorsal and
anal fins are more dominant than M. cuchia. The dorsal fin is slightly before position
from the anus (Fig. 4.8).
The gill arch is spiral and arranged in fibre-like fashion in M. cuchia and O. bengalense
respectively (Fig. 4.9). The mouth gape is broader in M. cuchia than in O. bengalense
(Fig. 4.10).
Fig. 4.9. Gill arch of M. cuchia (left) and O. bengalense (right).
Fig. 4.10. Mouth gape of M. cuchia (left) and O. bengalense (right).
The teeth of M. cuchia are relatively large and are countable while the teeth of O.
bengalense are very small in size and are not countable (Fig. 4.11).
Fig. 4.11: Teeth of M. cuchia (left) and O. bengalense (right).
In the stomach of M. cuchia, no other structure is attached with intestine. In case of O.
bengalense a long fat like structure is attached with intestine (Fig. 4.12)
Fig. 4.12: Fat like organ in the stomach of O.bengalense.
4.3. Meristic characters Efficiency of the allometric formula in removing size effect from the data was justified
by using correlation between total length and the adjusted meristic character. Total length
were excluded first and not transformed because using this parameter as standard all
other parameters were standardized. After the allometric transformation, the correlation
results revealed that all of the meristic variables studied were free from the influence of
size.
The mean number of line in body, number of line below head, number of teeth (upper
jaw), number of teeth (lower jaw) and number of gill racker were 6.0±0, 21.94±2.06,
17.47±2.97, 26.66±4.57 and 8.0±0 respectively in M. cuchia. Whereas the mean number
of line below head and gill racker was 10.21±0.631 and 8.0±0, respectively in O.
bengalense (Table 4.2). The mean number of line below head were significantly (Mann-
Whitney U test; z= -6.091; P<0.001) different between the two species (Table 4.2).
Table 4.2. Comparison of meristic counts between M. cuchia and O. bengalense (Mann-
Whitney U) (minimum and maximum values are in parenthesis)
Meristic characters M. cuchia O. bengalense Z-statistic Significance
No. of line in body
No. of line below head
6.0±0
(6-6)
21.94±2.06
(20-27)
-
10.21±0.631
(10-12)
-
-6.091
-
0***
No. of teeth (upper jaw) 17.47±2.97
(13-24)
- - -
No. of teeth (lower jaw) 26.66±4.57
(17-36)
- - -
No. of gill racker 8.0±0
(8-8)
8.0±0
(8-8)
0 1.0
***P<0.001
4.4. Morphological and landmark differences As for meristic characters are concerned none of the characters were found to be
significantly correlated (P<0.05) with total length, indicating that size effects had been
removed from the morphometric and landmark variates.
Sexes were determined by macroscopic examination of the respective gonads and this
subset was used to test hypothesis of no sexual dimorphosim in morphometric and
meristic characters of both the species. No meristic heterogeneity was observed among
the sexes in both the species.
Among the thirty five transformed morphometric (27 characters) and truss measurements
(8 characters) of M. cuchia, two morphometric measurements (Eye diameter, t = -2.34;
P<0.05 and Pre orbital length, t = -2.12; P<0.05) and one truss measurement (4-6, t =
2.09; P<0.05) were found significantly different among the sexes of M. cuchia (Table
4.3). Therefore, those characteristics were excluded for further analyses.
Table 4.3. Comparison of adjusted morphological and landmark measurements between
sexes of M. cuchia (Mean ± SD)
Characters
Sexes t-statistic Significance
or
Probability M F
Morphological characters
Pre dorsal length 47.43±5.16 47.02±2.68 0.26 0.795
Post dorsal length 13.57±1.68 13.10±1.70 0.76 0.453
Pre anal length 44.40±1.11 45.22±1.27 -1.94 0.062
Post anal length 14.15±2.22 13.87±1.30 0.41 0.681
Length of lateral line 53.84±3.30 55.24±1.19 -1.46 0.155
Head length 4.12±0.69 4.18±0.26 -0.32 0.755
Snout length 1.18±0.16 1.21±0.21 -0.44 0.666
Upper jaw length 2.42±0.21 2.52±0.33 -1.00 0.325
Lower jaw length 2.38±0.26 2.48±0.43 -0.78 0.443
Mouth gap 1.85±0.46 1.84±0.42 0.08 0.937
Eye diameter 0.50±0.12 0.60±0.14 -2.34 0.026*
Head depth 2.03±0.20 2.03±0.30 0.02 0.988
Head width 2.10±0.15 2.19±0.20 -1.47 0.153
Pre orbital length 1.00±0.16 1.21±0.37 -2.12 0.042*
Post orbital length 2.93±0.34 2.91±0.23 0.21 0.837
Greatest body depth 2.52±0.33 2.46±0.35 0.48 0.636
Least body depth 2.04±0.13 2.01±0.15 0.63 0.536
Greatest width of body depth 1.99±0.20 2.09±0.17 -1.58 0.125
Highest body diameter 7.96±0.70 8.17±0.68 -0.86 0.399
Width of body at vent 1.43±0.34 1.60±1.07 -0.63 0.534
Depth of body at vent 2.27±1.05 2.10±0.39 0.58 0.568
Distance between vent and
commencement of dorsal fin
2.30±0.74
2.26±0.42 0.17 0.866
Intestine length 18.54±3.29 17.82±4.79 0.51 0.617
Length beside lateral line-1 3.64±0.89 3.82±0.61 -0.62 0.541
Length beside lateral line-2 6.87±0.75 7.17±1.00 -0.96 0.345
Length beside lateral line-3 3.87±1.25 3.60±0.90 0.66 0.512
Length beside lateral line-4 7.42±0.60 7.74±0.85 -1.25 0.221
Landmark distances
1-2 4.06±0.50 4.24±0.50 -1.01 0.319
1-3 4.23±0.43 4.20±0.46 0.19 0.849
2-3 2.45±0.54 2.41±0.41 0.19 0.849
2-4 40.75±2.38 40.83±3.60 -0.08 0.938
3-5 42.41±2.34 42.05±2.08 0.45 0.658
4-5 2.50±0.81 2.27±0.46 0.93 0.360
5-6 13.17±1.49 12.84±1.94 0.54 0.590
4-6 14.57±1.02 13.83±0.89 2.09 0.045*
M: Male; F: Female
*P<0.05
Among the thirty two transformed morphometric (24 characters) and truss measurements
(8 characters) of O. bengalense, two morphometric measurements (Lower jaw length, t =
2.73; P<0.05 and Eye diameter, t= -2.24; P<0.05) were found significantly different
among the sexes (Table 4.4.). Therefore, those characteristics were excluded for
discriminant analyses for both the species. None of the truss measurements were found
significantly different between sexes of O. bengalense.
One morphological character, fat length of O. bengalense was not found in M. cuchia and
four morphological characters (Length beside lateral line 1, 2, 3 and 4) in M. cuchia were
not found in O. bengalense, therefore, those characters were not included for
discriminannt analyses or to determine the difference between the species.
Table 4.4. Comparison of adjusted morphological and landmark measurements between
sexes of O. bengalense (Mean ± SD) (Independent samples t-test)
Characters
Sexes
t-statistic Significance M F
Morphological characters
Pre dorsal length 45.12±4.02 44.72±2.56 0.25 0.808
post dorsal length 16.14±1.65 16.10±1.19 0.06 0.954
Pre anal length 43.40±0.84 43.78±0.53 -1.14 0.271
post anal length 15.48±0.84 15.13±0.58 0.99 0.336
Length of lateral line 54.09±0.46 54.00±0.68 0.27 0.789
Head length 3.76±0.23 3.81±0.33 -0.34 0.741
Snout length 0.96±0.24 1.08±0.17 -1.14 0.271
Upper jaw length 2.29±0.24 2.10±0.16 1.93 0.072
Lower jaw length 2.21±0.21 1.88±0.24 2.73 0.015*
Mouth gap 1.81±0.21 1.50±0.39 1.67 0.116
Eye diameter 0.43±0.05 0.56±0.13 -2.24 0.041*
Head depth 1.94±0.19 2.15±0.25 -1.62 0.127
Head width 1.86±0.21 2.03±0.33 -1.06 0.306
Pre orbital length 0.85±0.25 0.76±0.18 0.87 0.399
Post orbital length 3.00±0.23 3.02±0.20 -0.18 0.861
Greatest body depth 2.16±0.19 2.36±0.43 -0.97 0.346
Least body depth 1.86±0.49 1.80±0.40 0.26 0.802
Greatest width of body depth 1.77±0.33 2.06±0.33 -1.64 0.123
Highest body diameter 7.59±1.11 7.45±0.91 0.28 0.782
Width of body at vent 1.24±0.26 1.36±0.41 -0.62 0.542
Depth of body at vent 1.85±0.37 1.96±0.29 -0.66 0.521
Distance between vent and
commencement of dorsal fin
2.31±0.52
2.41±0.27 -0.50 0.623
Intestine length 19.79±0.37 21.17±1.64 -1.83 0.087
Fat length 24.33±2.78 25.87±1.16 -1.66 0.118
Landmark distances
1-2 4.36±0.32 4.17±0.24 1.34 0.201
1-3 4.28±0.37 4.22±0.32 0.35 0.729
2-3 2.36±0.31 2.44±0.27 -0.49 0.633
2-4 42.38±5.91 40.06±4.30 0.91 0.378
3-5 39.42±3.99 38.18±2.64 0.77 0.456
4-5 2.33±0.32 2.68±0.31 -2.12 0.051
5-6 16.59±1.53 15.99±1.46 0.75 0.463
4-6 15.94±1.05 15.17±1.17 1.26 0.226
M: Male; F: Female
*P<0.05
Table 4.5. Means and standard deviation of adjusted morphological data for M. cuchia and
O. bengalense (t-test for difference before and after adjustment of the variables)
Characters M. cuchia O. bengalense t-
statistic Significance
PDL 47.26±4.28 44.84±2.92 2.09 0.042*
PoDL 13.38±1.68 16.12±1.28 -5.86 0***
PAL 44.73±1.23 43.66±0.63 3.35 0.002**
PoAL 14.03±1.88 15.23±0.65 -2.53 0.015*
LAL 54.41±2.71 54.02±0.61 0.58 0.568
HL 4.14±0.55 3.80±0.30 2.39 0.021*
SnL 1.20±0.18 1.05±0.20 2.71 0.009**
UJL 2.46±0.27 2.16±0.20 4.15 0***
MG 1.84±0.44 1.59±0.37 2.02 0.049*
HD 2.03±0.24 2.09±0.25 -0.83 0.411
HW 2.14±0.17 1.98±0.30 2.34 0.023*
PoOrl 2.92±0.29 3.02±0.20 -1.19 0.242
GBD 2.50±0.33 2.30±0.38 1.90 0.064
LBD 2.03±0.14 1.82±0.41 2.72 0.009**
GWD 2.03±0.19 1.97±0.35 0.74 0.465
HBD 8.04±0.69 7.49±0.94 2.35 0.023*
WBV 1.50±0.72 1.33±0.37 0.93 0.356
DBV 2.20±0.84 1.92±0.31 1.31 0.195
DBCB 2.29±0.62 2.38±0.35 -0.56 0.578
IL 18.24±3.91 20.76±1.52 -2.55 0.014*
1-2 4.14±0.50 4.23±0.27 -0.69 0.491
1-3 4.22±0.44 4.24±0.32 -0.16 0.878
2-3 2.43±0.48 2.42±0.27 0.15 0.884
2-4 40.78±2.88 40.74±4.75 0.03 0.974
3-5 42.27±2.21 38.54±3.02 4.94 0***
4-5 2.41±0.69 2.58±0.35 -0.93 0.355
5-6 13.03±1.67 16.17±1.46 -6.53 0***
*P<0.05; **P<0.01; ***P<0.001
Independent sample t test showed that fourteen morphometric characters Pre dorsal
length (PDL), t test = 2.09; P<0.05; Pre anal length (PAL), t test = 3.35; P<0.01; Post
dorsal length (PoDL), t test = -5.86; P<0.001; Post anal length (PoAL), t test = -2.53;
P<0.05; Head length (HL), t test = 2.39; P<0.05; Snout length (SnL), t test = 2.71;
P<0.01; Upper jaw length (UJL) t test = 4.15; P<0.001; Mouth gape (MG), t test = 2.02;
P<0.05; Head width (HW) t test = 2.34; P<0.05; Least body depth (LBD), t test= 2.72;
P<0.01; Highest body diameter (HBD) t test = 2.35; P<0.05; Intestine length (IL) t test =
2.55; P<0.05 and two truss measurement 3-5, t test = 4.94; P<0.001; 5-6, t test = -6.53;
P<0.001 revealed a significant variation between two species in varying degrees (Table
4.5). Length of lateral line (LAL), t test = 0.58; P=0.568; Head depth (HD), t test= -0.83;
P=0.411; Post orbital length (PoOrL) t test = -1.19; P=0.242; Greatest body depth
(GBD), t test = 1.90; P=0.064; Greatest width of body depth (GWD), t test =0.74;
P=0.465; Width of body at vent (WBV), t test = 0.93; P=0.356; Depth of body at vent
(DBV), t test =1.31; P=0.195; Distance between vent and commencement of dorsal fin
(DBCB), t test = -0.56; P=0.578 and five truss measurement 1-2, t test = -0.69; P=0.491;
1-3, t test= -0.16; P=0.878, 2-3, t test =0.15; P=0.884, 2-4, t test =0.03; P=0.974, 4-5, t
test = -0.93; P=0.355 did not varied significantly between two species (Table 4.5).
Univariate statistics (ANOVA) showed that tweleve morphometric characters (PDL, F=
4.352; P<0.05; PoDL, F=34.289; P<0.001; PoAL, F= 6.404; P<0.05; HL, F=5.707;
P<0.05; SnL, F=7.326; P<0.01; UJL, F=17.219; P<0.001; MG, F=4.089; P<0.05; HW,
F=5.491; P<0.05; LBD, F=7.406; P<0.01; HBD, F=5.539; P<0.05; IL, F=6.485;
P<0.05) and two truss measurement (3-5, F=24.392; P<0.001; 5-6, F=42.58; P<0.001)
revealed a significant variation between two species in varying degrees (Table 4.6). eight
morphometric characters (LAL, F=0.331; P=0.568; HD, F=0.687; P=0.411; PrOrL,
F=1.405; P=0.242; GWD, F=0.543; P=0.465; WBV, F=0.867; P=0.356; GBD, F=3.603;
P=0.064; DBV, F=1.726; P=0.195; DBCB, F=0.314; P=0.578) and five truss
measurements (1-2, F=0.481; P=0.491; 1-3, F=0.024; P=0.878; 2-3, F=0.021; P=0.884;
2-4, F=0.001; P=0.974; 4-5, F=0.871; P=0.355 did not varied significantly between two
species (Table 4.6).
Table 4.6. Univariate statistics (ANOVA) testing difference between M. cuchia and O.
bengalense (df1=1; df2=47)
Characters Wilks' Lambda F Significance
PDL 0.915 4.352 0.042*
PoDL 0.578 34.289 0***
PAL 0.807 11.216 0.002**
PoAL 0.88 6.404 0.015*
LAL 0.993 0.331 0.568
HL 0.892 5.707 0.021*
SnL 0.865 7.326 0.009**
UJL 0.732 17.219 0***
MG 0.92 4.089 0.049*
HD 0.986 0.687 0.411
HW 0.895 5.491 0.023*
PoOrL 0.971 1.405 0.242
GBD 0.929 3.603 0.064
LBD 0.864 7.406 0.009**
GWD 0.989 0.543 0.465
HBD 0.895 5.539 0.023*
WBV 0.982 0.867 0.356
DBV 0.965 1.726 0.195
DBCB 0.993 0.314 0.578
IL 0.879 6.485 0.014*
1-2 0.99 0.481 0.491
1-3 0.999 0.024 0.878
2-3 1 0.021 0.884
2-4 1 0.001 0.974
3-5 0.658 24.392 0***
4-5 0.982 0.871 0.355
5-6 0.525 42.58 0***
*P<0.05; **P<0.01; ***P<0.001
First three canonical discriminant functions were used in the analysis. Pooled within-
groups correlations between discriminant variables and DFs revealed that four
morphometric characters (PoDL, UJL, PAL and IL) and two landmark distances (5-6 and
3-5) contributed to the first DF and three morphometric characters (HW, LBD and MG) contributed second DF and six morphometric characters (HL, HBD, PoAL, SnL, PDL
and LAL) contributed to the third DF (Table 4.7) implying that these characters are the
most important in the description of population characteristics.
Table 4.7. Contribution of morphometric and truss measurements of M. cuchia and O.
bengalense to the canonical functions
Characters Function
DF1 DF2 DF3
5-6 -0.614* 0.093 0.204
PoDL -0.430* 0.122 -0.113
3-5 0.332* -0.084 0.176
UJL 0.309* -0.072 -0.069
PAL 0.223* 0.032 0.133
IL -0.195* -0.042 0.089
HW 0.167 -0.459* -0.022
LBD 0.145 -0.348* 0.335
MG 0.198 0.212* -0.199
HL 0.084 -0.016 0.700*
HBD 0.104 -0.169 .410*
PoAL -0.132 -0.007 -0.360*
SnL 0.251 0.143 -0.263*
PDL 0.115 -0.077 0.179*
LAL 0.063 0.039 -0.178*
Eigenvalue 6.59 3.37 0.21
% of Variance 64.8 33.2 2.0
Variables ordered by absolute size of correlation within function. * Largest absolute correlation
between each variable and any discriminant function. Plotting Discriminant function DF1 and DF2 showed a clear differentiation between the
species as well as between the stocks for both morphometric and landmark
measurements. For both morphometric and landmark measurements the first and second
DF accounted 64.8% and 33.2% of among group variability, explaining 98% of total
group variability. All the populations were clearly separated from each other in the
discriminant space (Fig. 4.13). This suggested that there was limited intermingling among
populations and the populations of the species were separated (Fig. 4.13).
Fig. 4.13. Sample centroids of discriminant function scores based on morphometric and truss
measurements -1. M. cuchia (Mymensingh), 2. M. cuchia (Dinajpur), 3. O. bengalense
(Satkhira), and 4. O. bengalense (Bagerhat).
A dendrogram based on morphometric and landmark distance data was shown for the
populations of both the species constructed one cluster and further divided into two
distinct sub-clusters. M. cuchia collected from Mymensingh and M. cuchia collected
from Dinajpur constructed one sub-cluster and O. bengalense collected from Satkhira and
O. bengalense collected from Bagerhat constructed another sub-cluster based on the
Distance of squared Euclidean dissimilarity (Fig. 4.14).
Distance of squared Euclidean dissimilarity
0 5 10 15 20 25
+---------+---------+---------+---------+---------+
3
4
1
2
Fig. 4.14. Dendrogram based on morphometric characters and landmark distances - 1. M. cuchia
(Mymensingh), 2. M. cuchia (Dinajpur), 3. O. bengalense (Satkhira), and 4. O.
bengalense (Bagerhat). A correct classification of individuals into their original population from leave-one-out-
classification varied between 93.3% and 94.1% by discriminant analysis and 95.9% of
individuals could be classified in their correct priori grouping (Table 4.8). The proportion
correctly classifies M. cuchia (collected from Dinajpur) into the corresponding original
group was the highest (93.3%) (Table 4.8).
Table 4.8. Correct classifications of individuals M. cuchia (collected from Mymensingh and
Dinajpur) and O. bengalense (collected from Satkhira and Bagerhat) into their original
population (leave-one-out-classification)
Population
Predicted Group Membership Total
1 2 3 4
Original Count 1 16 0 1 0 17
2 1 14 0 0 15
3 0 0 8 0 8
4 0 0 0 9 9
% 1 94.1 0 5.9 0 100
2 6.7 93.3 0 0 100
3 0 0 100 0 100
4 0 0 0 100 100
1. M. cuchia (Mymensingh), 2. M. cuchia (Dinajpur), 3. O. bengalense (Satkhira) and 4. O. bengalense
(Bagerhat))
CHAPTER VI
SUMMARY AND CONCLUSION
SUMMARY AND CONCLUSION Eels, a recent export item, though, have not yet been given any attention on its culture
and collection could be the only option to meet the export demand. Hence, Bangladesh
has great opportunity to develop eel farming industry and to enter in wider Asian and
European market if proper attempt could be taken. Domestication is the first step to bring
eels under aquaculture. Knowing morphological characters is also a prerequisite for
breeding in captivity. The morphological difference may be explained by the relationship
between geographical distance and differences in environmental adaptation over the
geographical distances.
This study was designed to investigate regional and population variations in
morphological traits in a natural environment of two similar eels - M. cuchia and O.
bengalense collected from four areas of Bangladesh. A simple design was constructed to
analyze the morphological, morphometric and meristic characters of two species. The
whole physical appearances were analyzed which help in specific identification of the
species. On the other hand, the length and weight are measured. The average length and
weight of M. cuchia were 62.74±6.84 cm and 547.03±271.48 g respectively and
53.12±5.27 cm and 161.76±33.21 g respectively for O. bengalense.
There were minor sex-dependent morphological differences detected in the present study.
The mean number of line below head were significantly (Mann-Whitney U test; z = -
6.091; P<0.001) different between two species. In M. cuchia, two morphometric
measurements Eye diameter, t = -2.34; P<0.05 and Pre orbital length, t = -2.12; P<0.05
and one truss measurement (4-6) t = 2.09; P<0.05 were found significantly different and
O. bengalense, six morphometric measurements Lower jaw length, t = 2.73; P<0.05 and
Eye diameter, t = -2.24; P<0.05 were found significantly different among the sexes of O.
bengalense.
For both sexes of two species, adjusted morphological data were analyzed and
Independent sample t test showed that fourteen morphometric characters, Pre dorsal
length (PDL), t test = 2.09; P<0.05; Pre anal length (PAL), t test = 3.35; P<0.01; Post
dorsal length (PoDL), t test = -5.86; P<0.001; Post anal length (PoAL), t test = -2.53;
P<0.05; Head length (HL), t test = 2.39; P<0.05; Snout length (SnL), t test = 2.71;
P<0.01; Upper jaw length (UJL) t test = 4.15; P<0.001; Mouth gape (MG), t test = 2.02;
P<0.05; Head width (HW) t test = 2.34; P<0.05; Least body depth (LBD), t test = 2.72;
P<0.01; Highest body diameter (HBD) t test = 2.35; P<0.05; Intestine length (IL) t test =
2.55; P<0.05 and two truss measurement (3-5), t test = 4.94; P<0.001; 5-6, t test = -
6.53; P<0.001 revealed a significant variation between two species in varying degrees.
For better understanding of differences of between M. cuchia and O. bengalense
univariate statistics (ANOVA) showed that eleven morphometric characters Pre dorsal
length (PDL), P<0.05; Post dorsal length (PoDL), P<0.001; Post anal length (PoAL);
P<0.05; Head length (HL); P<0.05; Snout length (SnL); P<0.01; Upper jaw length
(UJL); P<0.001; Lower jaw length (LJL); P<0.001; Head width (HW); P<0.05; Pre
orbital length (PrOrL); P<0.001; Least body depth (LBD); P<0.01; Highest body
diameter (HBD); P<0.05 and one truss measurement (3-5); P<0.001 revealed a
significant variation between two species in varying degrees.
Major differences in morphological traits between M. cuchia and O. bengalense are
determined by discriminant function analysis. For both morphometric and landmark
measurements the first and second DF accounted 64.8% and 33.2% of among group
variability. By this discriminant analysis it was clear that the population were limited
intermingling separated among population. A dendrogram based on morphometric and
landmark distance showing the population is distinctly distanced. In this study, we found
two distantly related fish species – distinguished at the level of population structure –
exhibited two types of body shape where M. cuchia is cylindrically elongated and O.
bengalense is round elongated. Many differences were found among the species from
head to tail. Differences also occur in meristic measurement such as there are no lines
present beside lateral line of O. bengalense but there are few in M. cuchia. Numbers of
line below head were arranging by distinctly different shape and varies also in number.
Other major morphological differences are found in eye, head shape, body shape,
distance between vent and commencement of dorsal fin. Minor differences were also
found all over the body of both of the species, O. bengalense at the upper lip has two
little barbells and mouth gape was much broader in M. cuchia fat like structure attached
with intestine in O. bengalense was one of the major characters of the species. The whole
measurement of the morphological character of both the species indicates that they are
morphologically separated from each other.
The present study dealt with the population structure of two cuchia from a phenotypical
point of view to determine the morphometric among the stocks. It revealed the
differences of morphological characteristics between two species. This has major
implications in understanding morphological diversity among population.The result
indicates differences in population and can be very important for further taxonomic and
genetic studies to know the exact population structure.
The results of the study are useful as baseline information of cuchia populations for
further studies. In both aquaculture and open-water management, it is essential to select
stocks with better features. More research especially genetic studies and investigations of
the impacts of geo-environmental factors is needed for conservation and mass seed
production of selected stocks to pave the way to saving the two valuable eel species from
extinction.
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APPENDICES