A COMPARITIVE STUDY ON THE MORPHOLOGICAL ADAPTATIONS OF

THE ALIMENTARY CANAL IN SARDINELLA LONGICEPS, THUNNUS

OBESUS, AND RASTRELLIGER KANAGURTA

ASHA SAMSupervising Teacher

Dr . SUNIL KUMAR

Dept :Of : Zoology

Catholicate college

OBJECTIVES OF THE STUDY

To compare the morphological adaptation of the alimentary canal in Sardinella longiceps,Thunnus obesus and Rastrelliger kanagurta.

To find the RLG value of three fishes.

INTRODUCTIONFishes are cold blooded gill-breathing , aquatic vertebrates, with

limbs represented by fins.

Fishes feed on a wide range of food material and obtain their

nourishment from plants as well as animals.

The food feeding habitat are related with the digestive system of

the fishes. Mainly alimentary canal structure varies in different

species of fishes.

And is generally adapted in relation to the food and feeding habits.

MATERIALS AND METHODS In the present study, three different species of marine fishes belonging to

the different food groups such as herbivore, carnivore, and omnivore were selected and there include Sardinella longiceps, Thunnus obesus, Rastrelliger kanagurta.

The fishes were selected based on the economic values and their availability throughout the year and their sizes of the three fishes were apt for dissection.

The fishes carefully dissected with scissors, needle etc. The fishes were also carefully measured for the total length, standard

length, total gut length, and mid width of the body. The Relative Length of Gut[RLG]was measured using the formula,

RLG= Length of alimentary canal

Standard length of fish

Fig 1: Sardinella longiceps

Fig 2:Thunnus obesus

Fig 3:Rastrelliger kankgurta

RESULT The morphological characteristics of the alimentary canal observed in the three

fishes are followed.

Sardinella longicepsIt is a herbivorous marine teleost which feeds mainly at night and may feed even

during day time.

Oropharynx: The mouth is narrow, palatal organs are well developed and minute pharyngeal

teeth is present.

Oesophagus: It is short and narrow and merges with the intestinal bulb with out demarcation.

Intestine: It is a long, thin walled and highly coiled in structure . The relative length of gut is

1.868.

Fig 4:Photograph showing uncoiled gut of Sardinella longiceps

Thunnus obesusTunas are highly carnivorous. They feeds mainly on smaller fishes , crabs ,larvae of prawns , marine organism etc.

Oropharynx:The mouth is large, like a grinning mouth. Lips are thin and hard .The upper and lower jaws are provided with teeth.

Oesophagus:It is long and distensible to facilitate swallowing of large prey. There is a small external constriction separating the oesophagus from the stomach.

Intestine:The intestine is small length forming just 2-3 coils .The relative length of gut is 0.272

Stomach:It has a true stomach and quite large It is nearly Y-shaped.

 Fig 5:Photograph showing uncoiled gut of Thunnus obesus

Rastrelliger kanagurta Indian mackerel consisting of the phytoplankton and zooplankton. It

is a omnivore, feeding on algae ,aquatic plants , insects, micro crustaceans and larvae of prawn.

Oropharynx: Mouth is moderate and is bounded by soft, thin, unfringed lips.

Oesophagus: It is short and slight muscular in nature.

Intestine: Medium sized and it is thin walled and uniform diameter throughout

the length.The relative length of gut is 1.033.

 Fig 6: Photograph showing uncoiled gut of Rastrelliger kanagurta.

Int-Intestine:Os-Oesophagus:St-Stomach:Rct-Rectum:Pyl.ca-Pyloric caecae.

Sardinella longiceps Thunnus obesus Rastrelliger kanagurta

Fig 7:Diagrammatic representation of the uncoiled guts of the 3fishes studied.

Table 1:Feeding habits and morphology of mouth parts of the three fishes.

SPECIES FEEDING MOUTH TEETH PALATAL

ORGANS

GILL

RAKERS

S. longiceps Herbivore Narrow,sub

terminal,

Minute Pharyngeal

teeth.

Well developed Closely set to

form a fine

sieve.

T.obesus Carnivore Mouth large

with wide gap.

Nearly21canines

present .

Poorly

developed

Long hard

teeth .

R.kanagurta Omnivore Moderate

Anterior , soft

thin un fringed

lips

Fine teeth are

Present.

Thick paiatal

organ

Short and

stumpy

NAME OF FISH FEEDING HABIT {R.L.G}

Sardinella longiceps Herbivore 1.868

Thunnus obesus Carnivore 0.278

Rastrelliger kanagurta Omnivore 1.033

Table 2: Comprehensive table showing feeding habit and Relative Length of Gut {R.L.G.}.

The graph showing the R.LG value of three fishes.

Herbivore Carnivore Omnivore Sardinella longiceps Thunnus obesus Rastrelliger kanagurta

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2 {R.L.G}

{R.L.G}

DISCUSSION

The structure of the alimentary canal varies in different species of fishes, is generally adopted in relation to the food and feeding habits.

The adaptations of the alimentary canal of fishes of their food are particularly evident in the form of mouth, size, shape and structure of the oropharynx, structure of the oesophagus , presence or absence and shape of stomach and the intestine and relative length of gut.

The short and nearly straight intestine is seen in carnivorous and predatory fishes, but long, thin walled and highly coiled in the herbivorous species . The omnivorous species show an intermediate condition.

The relative length of gut was highest in Sardinella longiceps1.868.It decreased to 1.033 for Rastrelliger kanagurta and the lowest , 0.272 was recorded for Thunnus obesus.

CONCLUSION

It can be concluded that of the three fishes studied, the Relative Length of Gut was highest in Sardinella longiceps1.868.It decreased to 1.033 for Rastrelliger kanagurta and the lowest, 0.272 was recorded for Thunnus obesus.

The morphological variations present in the structure of the alimentary canal being morphologically very well adapted to the mode of feeding of these three fishes. These adaptations are very important to a fish from the survival point of view.

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