カワムツ、コイおよびハゼ科ヨシノボリ属における側線の形態学的特徴

誌名誌名 水産増殖 = The aquiculture

ISSNISSN 03714217

著者著者

渡邉, 賢二安樂, 和彦Monteclaro, H.M.Babaran, R.P.

巻/号巻/号 58巻1号

掲載ページ掲載ページ p. 25-35

発行年月発行年月 2010年3月

農林水産省 農林水産技術会議事務局筑波産学連携支援センターTsukuba Business-Academia Cooperation Support Center, Agriculture, Forestry and Fisheries Research CouncilSecretariat

Aquaculture Sci. 58 (1)， 25 -35 (2010)

Morphological Characteristics of I.ateralline

in Three Species of Fish

Kenji WATANABE1， Kazuhiko ANRAKU1，*， Harold M. MONTECLAR01

and Ricardo P. BAB皿 AN2

Abstract: The results presented herein report quantitative da阻 relativeto the distribution and morphological characteristics of superficial neuromasts (SNs) and canal pores (CPs) in goby Rhinogobius sp.， common carp Cyprinus carPio and dark chub Zacco temminckii. Using scanning electron microscopy， large ca叩 anddark chub were observed to possess more SN per cana1 scale compared to their small counterparts. Among the three species， ca叩 consistent1yhad the highest number of SNs and CPs. However， the density of SNs in SN司bearingscales is quite similar among the three species， even though the totallength of goby was only a third of the two other species. 百lenumber and dis仕ibutionof SNs and CPs on the surface ofthe head， the仕unkand caudal宣nvaried among species. Orientation of cells within SNs on the head showed various directions rela-tive to the fish body axis. On the廿unkand caudal五n，most of the sensory epithelia on the neuro-masts had orientations parallel the宣shbody axis although a number of those on the trunk in ca叩and dark chub were oriented dorso-ventrally. The possible relationship between the various勿pesof lateralline and lifestyle of each species is discussed.

Key words: Lateralline; Superficial neuromast; Canal pore

The lateral line is a unique mechanosensory

system in aquatic animals， such as fish and

amphibians. It is generally recognized as a water

vibration detector and has an important role

in schooling (Pitcher et al. 1976; Partridge and

Pitcher 1980)， food searching (Enger et al. 1989;

Baker et al. 2002; New 2002)， and mating (Satou

et al. 1994). The receptors are the superficial

neuromasts (SN) and canal neuromasts (CN) ，

both of which have rod-like gelatinous cupulae

that encapsulate apical projections of the hair

cells. SN s occur superficially on the surface of

the skin wi出仕lecupula protruding directly into

the ambient water while CNs are located within

由ecanal tube beneath the subdermal type.百le

functional difference between the two neuromast

types became apparent in recent years and has

con凶butedto a be仕erunderstanding of the role

of吐lelateralline in animals.τbeoretical analyses

Received September 18， 2009: Acceptβd November 18， 2009.

and direct measurements of cupula motion have

indicated that SN s and CN s work as water veloc-

ity and acceleration detectors， respectively

(van Netten and Kroese 1987，1989; Denton and

Gray 1988，1989; Kalmijn 1989; van Netten 1991).

These results were confirmed in an electrophysi-

ological study (Kroese and Schellart 1992) while

more recent studies have revealed the minute

functions of both neuromasts in f10wing water. Montgomery et al. (1997) demonstrated that

SN s mediate the rheotactic behavior under a

low f10w of water. Engelmann et al. (2000， 2002)

studied the electrophysiological response char-

acteristics of the lateral line peripheral nerve

宣bersand suggested白atSNs are f1ow-sensitive and白ata constant f10w could mask the sensory capabi1ities of SN s during stimulation but not

CN s， which are insensitive to f1ow. Krother et al. (2002) also indicated that the same response

1 Faculty of Fisheries， Kagoshima University， Shimoarata 4-50-20， Kagoshima 890-0056， J apan. 2 College of Fisheries and Ocean Sciences， University of the Philippines Visayas， Miagao， Iloilo 5023， Philippines. * Corresponding author: Tel: (+81) 99-286-4242; Fax: (+81) 99-286-4015; E-mail: anraku@fish.kagoshima-u.ac必。ιAnr北u).

26 K.羽Tatanabe，K. Anraku， H. M. Monteclaro and R. P. Babaran

characteristics that were observed peripher-

ally are maintained in the medial octavolateralis

nuc1eus of the central nervous system.

The evolutional deve10pment of the neuro-

masts is becoming c1earer but knowledge on

the distribution of these receptor cells among

different :fish species is sti11 limited， especially

on the relevance of neuromast characteristics

in :fish ecology and behavior (e.g.， habitat，

feeding style， etcふWebb(1989) reviewed the

development of the canal system in :fishes and

suggested a c10se correlation between the varia-

tion of canal formation and ecological habitat，

inc1uding hydrodynamic environment. In this

study， we examined the SNs and CPs in three

:freshwater species that inhabit different hydro-

dynamic environments and attempted to cor-

relate the abundance， sensory polarities and

distribution of neuromasts with their different

lifes匂rles.百lethree species were goby (a sed-

entary species living in relatively shallow lentic

environment)， common ca叩 (acyprinid species

which is relatively slow swimming and prefers

to stay in lentic waters) and dark chub (another

cyprinid but is an active species， fast swimmer

and stays in lotic habitat). A1so， we compared

the distribution of SNs between large-and

small-sized individuals. These results wi11 be

useful for future studies regarding the function

and evolution of the neuromast systems in :fish.

Materials and Methods

Testanimαls The species examined were goby Rhinogobius

sp. (TL 46 mm)， common ca叩 Cyprinuscarpio (TL 86， 149 mm) and dark chub Zacco tem-minckii (TL 56，145 mm). Goby and dark chub were captured in the 0 and Koutsuki rivers，

respective1y， in Kagoshima， J apan; common

carp were purchased :from an ornamental :fish

shop. Based :from its ovary， the goby was con開

sidered mature; however， no juveni1e goby was

available for this study. A11 species were tempo同

rari1y he1d in a tank and fed with commercial

pellets before宣xationfor scanning electron

microscopy (SEM) examination.

SEMρrepαrations

Samples of the epithelium were prepared by

cutting the entire left side of :fish body， inc1ud-

ing :fins， into pieces measuring about 1 cm2 after

the :fish were killed following anesthetization

with ice water. The cut pieces were :fixed in 2.5%

glutaraldehyde in PBS solution (0.1 mM， pH

7.2). After 24 h， :fixed samples were rinsed in

PBS， dehydrated in ethanol series， dried using

t-BuOH :freeze dryer (VFD・21S，Vacuum Device

Co.， Ltd.， Ibaragi， Japan)， and gold-coated

(Magnetron spa仕erMSP-10， Vacuum Device

Co.， Ltd.， Ibaragi， Japan). SEM (Hitachi S-4100，

Tokyo， Japan) observations were performed all

over the skin surface of the :fish.

To make a quantitative examination of neuro-

masts in small-sized ca叩 andlarge-sized dark

chub， twenty canal scales and thirty non-canal

scales were randomly selected， prepared and

examined :from both species.

Neuromast anαlyses The number of SN s and CPs were counted

based :from the SEM observations. 1ρcations

of the SN and CP were plo仕edonto whole body

photographs of the experimental subjects.

For each SN， sensory polarities were judged

according to the orientation of hair cells.

Results

Morphology 01 superficial neuromasts and canαl pores

Figure 1 shows the SNs and CPs observed

on the surface of goby head. Large-sized SNs

were conspicuously present， occurring in lines

(Fig. 1A). SNs distributed along the edge of

the preopercular bone toward the lower jaw

were especially prominent. These were slightly

sunken under the epidermis (Fig.1B) and

were arranged in two rows. On the sensory

epithelium of each SN， hair cells consisting of a

kinocilium and a group of stereoci1ia with many

microvillous supporting cells were observed

(Fig. 1C). CPs were found on the supraorbital

region and in :front of the nares， but not on the

in:fraorbital and mandibular regions. The infra-

orbital， preopercular and mandibular canallines

Morphological Characteristics of Lateral Line 27

were replaced by the alignment of the SNs. On

the trunk region， the SNs were found on the epidermis where they were organized into a

dorsoventralline at the anterior portion of the

scales (Figs. 2A， 2B). The sensory epithelia of the SN s were diamond-shaped with c1ear long and short axes (Fig. 2C). The shortぉdswas

parallel to the longitudinal body axis of fish.

Hair cells were also or・ientedparallel to the

short axis of the epithelium SNs (Fig. 2D). On

the surface of the caudal fin，出TOlong lines of

SNs were observed (Figs. 3A， 3B). The epithe-

lia were round and the hair cells were oriented

paralle1 to the fish body axis (Fig.3C). CPs

were not found on the surface of the trunk and

caudal fin of goby. Instead， the trunk canal was

replaced by SNs although it showed incomplete

canal patters.

An extensive arrangement of SNs and CPs over

the surface of the head was observed in ca叩 σig.

4). CPs were distributed in rows that formed canal

lateral lines at the supraorbital， in企aorbital，otic，

preopercular， mandibular， postotic， supratemporal

Fig. 1. Scanning electron microscopy images showing the s叩p呂杭ti凶aldiゐst廿riぬbu凶1此tiぬon0ぱfs叩upe臼rficialn犯削e創ur刀r羽 na出stおs(S トN閃Jり)and canal pores (CP) on the surface of Rhinogobius sp. head. A， Arrows indicate CPs while depressed circular areas (e.g.， enc10sed in a square) contain SNs; B， An SN slightly sunken under the epidermis; C， A c10ser view of the sen-sory epithelium of the SN which consisted of hair cells with a kinocilium and a group of stereocilia.

and temporal portion of the main trunk canal.

The SNs around the nares were generally dis-

tributed in front of the anterior nostril (Fig. 4A).

Numerous SNs around the CPs and on the gill

cover wer・ealigned at right angles to the canal

line (Fig. 4B) and at the edge of the gill cover

(Fig. 4C). The sensory epithelia were oval in

shape with different orientations at each loca-

tion on the head (Figs. 4B， 4D， 4F). Figure 5

shows both SNs and CPs over the surface of

the trunk and caudal fin in ca叩・ Aseries of

canal scales， each bearing a single pore， were

Fig. 2. Superficial neuromasts distributed on a trunk scale in Rhinogobius sp. A， SNs lie at the anterior portion of the trunk scale; B， Arrows indicate the perpendicular alignment of SNs; C， Diamond-shaped sensory neuro同

masts along the trunk; D， The inner sensory epithelium along the trunk.

Fig. 3. Superficial neuromasts distributed on the caudal fin of Rhinogobius sp. A， Broken lines indicate two rows of superficial neuromasts on the fin rays; B， Arrows indicate the rostro-caudal alignment of SNs; C， Circular sensory epithelium of SN on the caudal fin.

28 K. Watanabe， K. Anraku， H. M. Monteclaro and R. P. Babaran

observed in the center of the trunk region

along the body axis (Fig. 5A). Most of these

canal scales， including several non幽 canalscales，

contained SN s (Figs. 5A， 5C). In both scale

types， the sensory epithelia were oval in shape

however their orientations were different. On

canal scales， the sensory epithelial short axis

was parallel to the bodyおせら whileon no任 canal

scales， they were perpendicular to the body axis

of :fish (Figs. 5B， 5D). On the caudal :fin surface，

CPs were absent while the SNs occurred in

rows in between the :fin rays (Figs. 5E， 5F).

Figures 6 and 7 show the distribution of SNs

and CPs on dark chub head and trunk surface，

respectively. The arr溜 1gementof the CPs was

similar with common car下 inboth head and

trunk regions (Figs. 6A， 7 A). Majori句Tof the

C

Fig. 4. Distributions of superficial neuromasts (indicated by closed arrows) and canal pores (indicated by open arrows) on the head surface of Cyprinus carPio. A， The region fronting the nostril; B， Orientation of sensory epi-thelia found in A; C，τne region in the preopercular bone; D， Orientation of sensory epithelia found in C; E， The region in the opercular bone; F， Orientation of sensory epi-thelia found in E.

Fig. 5. Superficial neuromasts (indicated by closed arrows) and canal pores (indicated by open arrow) on the trunk and caudal fin of Cyprinus caゆio.A， A canal scale with SNs and a CP; B， Sensory epithelia on a trunk canal scale; C， A non-canal scale with cupula; D， Sensory epithe-lia on a trunk non-canal scale; E， SNs along the caudal fin; F. Sensory epithelia along the caudal fin.

Fig. 6. Superficial neuromasts (indicated by closed arrows) and canal pores (indicated by open arrows) on the head surface of Zαcco temminckii. A， Distribution of CPs; B， A CP and several SNs around the nostril; C， Sensory epithelium of SN shown in B; D， Neuromasts along the preopercular bone; E， SNs along the opercular bone.

Morphological Characteristics of Lateral Line 29

Fig. 7. Superficial neuromasts (indicated by closed arrows) and canal pores (indicated by open arrows) on the trunk region of Zacco temminckii. A， A series of CPs and SNs on trunk canal scales; B， Sensory epithelia of SNs on canal scales; C， SNs on trunk non-canal scales; D， Sensory epithelia of SNs on non-canal scales.

SNs were distributed along the canal lines on

the head and within the canal scales on the

trunk (Figs.6B， 6D， 7A). Other SNs were

observed on the opercular bone and on a few

norトcanalscales (Figs.6E， 7C). Notably， there

were no SN s on the ventral side of the trunk.

The SNs on the trunk were distributed perpen開

dicular to the fish body axis. Eight SN s and no

CPs were found on the caudal fin.

Distribution 01 SNs and CPs in large-αnd small-sized individuals The twenty canal scales and thirty non-

canal scales from the small carp had 104 and

64 SN s， respectively. Those from large dark

chub contained 147 and 0 SNs， respec註vely.

Comparisons on the mean number of SNs per

canal scale between large and small individuals

revealed significant differences (t-test， Pく0.05)

in both common ca叩 (9.7per scale and 5.2 per

scale， respectively) and dark chub (7.4 per scale

and 3.2 per scale， respectively). Regression

analyses between the total length and the total

number of SN s in all canal scales indicated that

SNs will be abundant in dark chub when total

length is less than 80 mm. In common carp，

the average number of SN s per non-canal scale

is higher in large-sized (7.1 per scale) than in

small-sized (4.6 per scale) individual. In dark

chub， the thir句Tnorトcanalscales examined from

the large司sizedindividual did not possess SNs

probably because the occurrence of SNs in

non-canal scales in this species is quite low， as

observed in small司zeddark chub where only

2% ofthe non幽 canalscales had SN s.

S戸αtialdistribution 01 SNs and CPsαmong species Spatial distributions of SNs and CPs in all spe-

cies examined are illustrated in Fig. 8 and the

results of quantitative measurements are shown

in Table 1. The arrangements of the canal line

were almost similar in common carp and dark

chub although the trunk canal was positioned

more ventrally in dark chub (Fig. 8). On the

head， the total numbers of CPs were 10， 58 and 41 in goby， carp and dark chub， respectively. On

the trunk， no CP was observed in goby while

37 and 47 were counted in caゅ anddark chub，

respectively (fable 1).百lemean diameters of

the CPs were almost the same on the head of all

Table 1. Comparison ofthe spatial distributions of canal pores (CPs) and superficial neuromasts (SNs) in three species of fish

Species (Scientific name)

Goby (Rhinogobius sp.DA) Commoncarp

(Cyprilllls carPio)

Darkchub gacωte1ll11lillckii)

Anterior lateralline Posterior lateralline

Canal scales (scales with CP) TL (mm) Num Num Mean

Mean Range of "T..~ _< Mean Range of of Num num Num .m"b~~' Num of diameter CP diameter CP scales of of SN of CP of SN canal of CP diameter v. v n ___1__ of CP diameter with SN per scales SN scale

46 10 0.10 0.06-0.16 173 。149 58 0.11 0.05-0.20 622 37 0.12 0.08-0.17 31 302 9.7

Scales without CP Caudal 在日

Num Mean Num of Num num Num

scales of SN of SN of SN scales with per

SN scale

260 26 196 7.5 55

375 114 805 7.1 73

56 41 0.09 O.Cら0.16 143 47 0.05 0.01-0.07 33 104 3.2 450 9 26 2.9 8

All data were obtained from the left side of a sagital1y halved fish.“-" indicates none. Canal pore (CP) diameter is expressed in mm.

30 K. Watanabe， K. Anraku， H. M. Monteclaro and R. P. Babaran

Rhinogobius sp. DA， T1-46mm

Cyprinus carpio， TL 149m

Zacco temminckii， TL 56mm

Fig. 8. Comparisons of the spatial distributions of superficial neuromasts and canal formations in Rhinogobius sp.， Cyprinus carpio and Zacco temminckii. Red and green dots show the CPs and SNs，

respectively. Shadowed scales indicate scales where SNs were present.

subjects， but much smaller on the仕unkcanal

in dark chub compared with that in carp (ιtest，

P<0.05) (Table 1). In dark chub， it is noted that

the mean diameter of the CPs on the head was

larger than those located on the甘unk(ιtest，

P<0.05). Typically， a canal neuromast is present

between two neighboring canal pores (Bamford

1941; Bialowiec and Jakubowski 1971)， thus it can be assumed that the total number of canal

neuromasts is similar with the number of canal

pores (and scales with canal pores).官lIsimplies

that compared with goby， the common carp and

dark chub had relatively more numerous canal

neuromasts， both in the head and trunk regions.

The number of SN s on the surface of the

head， trunk and caudal fin were 173， 196 and 55，

respectively， in goby; 622， 1107 and 73， respec-

tively in common carp; and 1434， 130 and 8，

respectively in dark chub (Table 1). The total

number of SN s on the entire side body surface

in the three species had the following order:

carp (1802) > goby (424) > dark chub (281).

Carp consistent1y had the highest number

of SNs over the head， trunk and caudal fin.

Accordingly， dark chub had the least SN s over

the three body regions. The proportion of canal

scales containing SNs was high (83.8% and

70.2% in carp and dark chub， respectively) but

only 10%， 30.4% and 2% of non-canal scales in

goby， carp and dark chub， respectively had SNs.

Interestingly， the average number of total SNs

per scale (canal and non-canal) is the same in

the 4らmmlong goby (7.5 per scale)， 149・mm

long common carp (7.6 per scale) and 145-mm

long dark chub (7.35 per scale).

Sensory polarities 01 superficial neuromasts

τbe sensory polarities of the SN s are indi-

cated in Fig. 9. On the head surface of all spe-

cies， the polarity of the SN s distributed around

the nostril region seemed tangential to the

nasal cavity. In goby， the sensory polarities of the two rows arranged along the lower jaw from

the opercular bone were different; the upper

31 Morphological Characteristics of Lateral Line

Fig. 9. Sensory polarities of super宣cialneuromasts in仕lethree species examined. Arrows indicate the direction of polarities.

宣nfollowed the same direction as the fin rays.

In this study， we describe the numbeれ dis開

tribution and orientation of superficial neuro-

masts and canal pores in three species of fish:

the goby Rhinogobius sp.， the common carp

Cyprinus carPio and the dark chub Zacco tem-minckii. A11 three species have a series of canals

over the head and along the trunk也atopen

through the pores (canal pores)， except the

goby which lacks canal pores on the trunk. A11

have superficial neuromast systems although

the total number in each species differs.These

superficial neuromasts句rpicallyoccur individu-

ally， or in rows， on the surface of the head， the

trunk and the caudal fin. Orientation of epithe-

lial cells within superficial neuromasts on the

head showed various directions， that is， rostro・

caudal， dorso-ventral and sometimes in approxi-

mately 450 angle relative to the fish body axis.

Schmitz et a1. (2008) suggested that the various

Discussion

row had a right-angled orientation relative to

the lower jaw， whi1e the lower row followed the

out1ine of the jaw. In ca叩 anddark chub， the

distributions of polarities on the head surface

were quite simi1ar. Most of the SNs around the eyeball showed polarities along the supraorbital

and infraorbital canals whi1e SN s a10ng the pre-opercular and mandibular cana1 showed polari-ties perpendicular to the canalline. Many of血e

sensory polarities of the SN s distributed over

the opercular bone region followed the direc-

tion of the edge of the opercular bone.

In goby， the polarities of all SNs dis仕ibuted

in the仕unkshowed the same direction as the

body axis. In ca叩 anddark chub， the distribu同

tion of polarities was quite simi1ar in both the head and trunk sections. Most of the SNs on

the latera1 line scales showed polarity along

the body axis， although a few had polarity in a

dorsoventral direction. In carp， most SN s dis-

tributed over the ventral side from the cana1line showed a polarity parallel to the body axis. In all

species， the polarities of the SN s on由ecaudal

4

、hi宅九四出川副劇

zsz

32 K. Watanabe， K. Anraku， H. M. Monteclaro and R. P. Babaran

orientations of the neuromasts on the宣shhead

is a result of the uneven surface on the head

and the non-linear distribution of由elateralline

canals， although the functional signi:ficance of

the patterns of neuromast orientation on the

fish head is still unknown. On the trunk and

caudal fin， most of the sensory epithelia on the

neuromasts have orientations parallel the fish

body axis while a number of those in common

ca叩 anddark chub are oriented dorso・ven仕ally.

These results are in agreement with the reported

orientation of sensory epithelia on superficial

neuromasts on仕1e廿unkof other species which

are either ros仕o-caudalor dorso-ven廿alin orien-

tation (Coombs et al. 1996; Coombs and Conley

1998). Super宣cialneuromasts wi血 rostro・caudal

oriented sensory epithelia are ideally suited to

measure flow fluctuations that travel from the

head to出etail of the fish.

Quantitative analyses of superficial neuromasts

in large-and small-sized individuals were per-

formed in common carp and dark chub.τbe aver開

age number of superficial neuromasts per scale

increased with fish size. This observation was

also reported in sea bass (Faucher et al. 2005).

One interesting result of出isstudy is出esimil訂ー

ity of the average number of superficial neuro-

masts among gobぁcommoncaゅ anddark chub

notwithstanding the relative differences in body

leng仕lS.官1esmaller， but mature goby does not

possess canal scales with super宣cialneuromasts，

but relatively high densities of super宣cialneuro-

masts are present in several non-canal scales.

Our results show that Rhinogobius sp. has fewer canal pores on the surface of the head

compared to the two other species studied.

Based on the c1assi宣cationofWebb (1989) on the patterns of canal structures姐 ddis仕ibutions，

these canals on the head are of reduced canal

type. Also on the head surface are a number of

super宣cialneuromasts that form a series of rows

and columns similar to the black goby Gobius niger (Marshall 1986).百1esesuperficial neuro-

masts have varying degrees of orientation. In

Rhinogobius sp.， two rows of sensory epithelia

lined along the lower jaw have opposite orienta-

tions， wi吐1one row able to respond to fore-to・a立

water movements while the other row more

sensitive to water movements in the up and

down direction. Previous reports on other goby

species showed that many lines of superficial

neuromasts on the head have sensitivities per-

pendicular to the fish body axis (Marshall 1986).

This suggests白atgoby' s neuromast system has

a bias for detecting vertical movement in water.

This arrangement must be an adaptation for the

goby which is generally sedentary and prefers to

stay near the bottom in low-current or still waters

while waiting for prey to come from the benthos.

Along its trunk， Rhinogobius sp. possesses supe子ficial neuromasts within non-canal scales. These

neuromasts have a ros廿o-caudalpolarity so that

hair cells give their greatest response to head-to-

tail water movement. But among the three spe-

cies studied， it is the only one that lacks canals

along the trunk thus is c1assi:fied as absent. Another goby species， the Bαthygobiusルscusalso lacked canals but were instead replaced by

numerous superficial neuromasts (Rouse and

Pickles 1991).官1eabsence of canals on仕1esur-

face of fish body has been reported in species

inhabiting dark habitats like deep-sea and caves (Parzefall1986; Marshall1996).官官 absenceof a

仕unklateralline in Rhinogobius sp. suggests that perception of water turbulence in仕1etrunk is not

necessary in its lifestyle probably because living

in solitary and in low-current waters does not

require these specialized organs.

Compared to the two other species， the

common carp has the highest number of super-

ficial and canal neuromasts， and has the high-

est proportion of canal and non-canal scales

containing superficial neuromasts along the

trunk surface. Carp has simple canals on the

head surface and complete canals along the

trunk which can be further c1assi:fied as com-plete straight. The abundance of superficial

neuromasts in c訂 pis similar with that reported

in another Cyprinidae family membeれthegold-

fish， with which it is capable of interbreeding

(Taylor and Mahon 1977). Puzdrowski (1989)

and Schmitz et al. (2008) reported that each

body side of gold宣shCarassius auratus has about 1，800 -2，000 superficial neuromasts dis凶buted

across the head， trunk and caudal曲1.Like the

gold:fish (Schmitz et al. 2008)， the most frequent

Morphological Characteristics of Lateral Line 33

orientation of the sensory epithelia of superfi-

cial neuromasts on the trunk of ca叩 isros仕0・

caudal， i.e.， parallel to the fish body axis. But

unlike the goldfish where a large proportion

of sensory epithelia on the仕unkcanal scales

have a dorso-ventral orientation， the sensory

epithelia of neuromasts on trunk canal scales

in car下 havea most1y rostro・caudalorientation.

The development of superficial neuromasts in

ca叩 hasbeen reported as early as its larval

stage with the number of neuromasts increas-

ing rapidly from the head to the trunk during

metamorphosis， where the neuromasts訂 epos-

sibly used to find a good substratum for attach-

ment and in finding food (Appelbaum and Riehl

199η.百lIsfish has well-developed chemosen-

sory organs， possessing numerous taste buds

and elongated olfactory pits. When scavenging

the bottom during feeding and especially under

dark conditions， the chemoreceptors would

probably be used to sense both non-motile and

moti1e partic1es whi1e the numerous canal neu-

romast systems on its head and trunk would be

bene五cialin detecting motile food items that

quickly dart from the bottom. A1so， common

ca叩 probablyuses its extensive cephalic line

to detect and analyze capi11ary waves like those generated by insect prey (Bleckmann et al.

1989). However， we cannot explain why the

commonca叩 possessesan abundance of super-

ficial neuromasts distributed all over its body

surface. This di1emma has also been noted in goldfish and other limnophi1ic fish species

(Schmitz et al. 2008).

The dark chub Zacco temminckii has simple

canals on the head surface and complete canals

along the trunk， which can be further c1assi:fied as ven仕aldisplaced straight. It has consider-

ably numerous canal pores distributed over its

head and along the trunk lateralline making the

dark chub particularly sensitive to changes in

the acceleration of water motion.τbis property

must be employed by the dark chub which has

an active lifestyle and exhibits dominance hier-

archy in its habitat. This species displays aggres-sive behavior against each other， e.g.， chase，

lateral display， parallel swim and butt (Katano

1985)， and during foraging and mating activities

(Katano 1998).百lenumber of canal pores in

dark chub and carp are relatively simi1ar. A1so a member of fami1y Cyprinidae， dark chubs

are widely distributed in the rivers and lakes of

eastern Asia and feed mainly on algae， aquatic

insects and small invertebrates. The trunk canal

lateralline in dark chub observed in this study

showed unique features. The trunk canal was

shifted towards the ventral side， suggesting that

they use the current f10w information below the body probably ωdetect the distance between

出ebody and the bottom. Among the three spe-

cies studied， the number of superficial neuro-

masts in dark chub was consistent1y the lowest

across the three body regions.

Clear1y， the morphological characteristics of

the lateralline system vary among the three spe-

cies studied.百lIsdifference of lateral line mor-

phology among fish species has been reported

in the past and had been partly attributed to

developmental and morphological constraints

(Coombs et al. 1988; Webb 1989). For canal

pores，出eiroccurrence and dis仕ibutionin goby，

common c訂 pand dark chub seem to be an

adaptation to their biological strategies， mainly

on their feeding and social behaviors which

are best complemented by these accelerator-

sensitive organs. For superficial neuromasts，

Coombs et al. (1988) suggested that the vari-

ous morphological patterns part1y represent an

adaptation to different hydrodynamical environ-

ments. Another hypothesis is that the superficial

neuromasts may also represent an adaptation

to a particular hydrodynamic environment (e.g.

low-f1ow versus fast~宜owwater) or to swimming

speed (e.g. fast versus slow swimmers). In his

review artic1e， Dijkgraaf (1963) discussed the

development of neuromast systems with special

reference to the interests of evolution， and pro-

posed that“bottom dwellers and slow or inter-

mittent1y swimming fishes living in quiet water

tend to have incomplete canals or no canals at

all and only free neuromasts like amphibians".

Our results showed血atcommon ca叩， a slow-

swimming species， has a higher abundance of

super宣cialneuromasts compared to血efast-

swimming dark chub. Gobies are probably

exceptions when comparing the abundance of

34 K.Wa句nabe，K. Anraku， H. M. Monteclaro and R P. Babaran

super:ficial neuromasts and their habitats as sug-

gested in the review of the functional morphol-

ogy and ecological correlation of lateral line by

J anssen (2004). Howeve乙morestudies involv-

ing more representative species are needed to

validate this hypothesis.

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カワムツ，コイおよびハゼ科ヨシノボリ属における

側線の形態学的特徴

渡遺賢二・安楽和彦・ HaroldM. MONTECLARO・RicardoP. BAB組釧

コイ科魚類のカワムツとコイ，ハゼ

丘と，側線管が体表で開く部位でで、ある側線孔について，それらの形態，分布，分布数，感度極性を電

子顕微鏡観察によって調べた。コイとカワムツの表在感丘数は体サイズの増加にともない増加した。

表在感正の頭部および体幹部での分布数はヨシノボリおよびカワムツで比較的類似したが，コイでの

分布数は明白に多かった。一方で， 1枚の鱗に分布する表在感丘数の平均は 3魚種で、大差はなかった。

側線孔はヨシノボリ属では頭部のみで認められ数は少なく，コイ，カワムツでは頭部と体幹部に広く

分布していた。表在感正の有毛細胞の分布から推定した表在感正の感度極性は， 3魚種において，頭

部でより多様な方向に感度を示し，体幹部および尾鰭に分布する感正は，多くが体軸と同じ方向に感

度を持ち，一部は背腹方向にも感度を持つことが示された。