Chapter V

CAPTIVE BREEDING AND SEED PRODUCTION

PROTOCOLS OF ETROPLUS SURATENSIS (BLOCH)

5.1. Introduction

Etroplus suratensis is essentially a brackish water fish that has become

naturally acclimatized to freshwaters. Being a high value fish that fetch a high

price, its capture fishery is exposed to high fishing pressures. The species has been

demonstrated to be an ideal candidate for pond culture (Sumitra Vijayaraghavan et

al., 1981) and most adapted for intensive farming in low volume high density

cages (Padmakumar et al., 2004). Although the fish breeds naturally in confined

conditions, production is most erratic; lack of required quantities of fish seed is the

most serious constraint for expansion of its culture. Popularization of commercial

farming depends largely on development of reliable method of seed production

under controlled conditions. Owing to their unique and prolonged parental care and

biparental substrate breeding habit, efforts for inducing them to spawn in captivity

has not been successful.

Propagation of pearlspot is hampered also due to a variety of reasons. In

nature, E. suratensis breeds in shallow, peripheral waters in isolated territories

(Samarakoon, 1985). Such shallow territories are the most seriously exposed to

human interferences. For example, in Vembanad lake, indiscriminate dredging of

sub fossil lime shell deposits for industrial use, by mechanized dredgers, almost

round the clock, bring about cataclysmic damages to the bottom substratum

breeding habitats of pearlspots (Padmakumar, 2003). Increased sedimentation and

siltation of the lake has been yet another factor detrimental to ‘pit caring’ and

‘parental care’, characteristic to this species. The long chain of canals in the

coconut gardens, adjoining the backwater stretches have been the natural breeding

grounds of this species. Unabated reclamation of these shallow wetlands and rapid

landfills during the past two decades in the name of ecotourism and development of

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resorts on the backwater front has been another factor that impeded their natural

recruitment. Further, with the boom in backwater tourism, the demand for

Pearlspot, the brand species of Vembanad, has increased tremendously. Being a

high value fish, selective fishing for this species has been most rampant. Another

persistent threat is from pollution, due to excessive use of chemical pesticides in the

adjoining rice polders for intensive rice farming. Near total disappearance of

E. suratensis in the vast inland water bodies of Kuttanad wetlands, upstream

Vembanad lake has also been attributed to persistent exposure to high concentration

of agricultural pollutants often higher than maximum allowable toxicant

concentration (Sulekha, 2001). Habitat protection and protocols for recruitment

through ranching are two recognised strategies for protection of endemic fish

species affected by habitat loss and hampered natural recruitment. This calls for

efforts to develop protocols for artificial breeding of this species.

5.2. Results

5.2.1. Collection and Maintenance of Brooders

A total of 385 mature fishes and 494 young ones, were collected and

conditioned to maturity in scientifically prepared holding ponds of size 250 sq.m, in

the Regional Agricultural Research Station, Kumarakom. As the fish preferred an

omnivorous diet, as evident from the food and feeding studies, in the holding ponds,

the broodstock was raised on natural algal production facilitated by organic

manuring, supplemented with commercial feed comprising rice bran, ground nut oil

cake and commercial pellet feed. An effective population size (Ne) of minimum

500 (FAO/UNDP, 1981) was maintained and utilized for the captive breeding

trials. E. suratensis stocks, when raised in pond conditions with adequate water

exchange facilities and nutritionally balanced diets was observed, to reach good

gonadal condition during the first year itself. Fishes were also found to breed

profusely in the broodfish ponds when nesting materials were provided to promote

natural breeding.

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5.2.2. Pond Breeding of E. suratensis

Breeding behavior of the fish, closely monitored in an earthen pond

revealed that the breeding activities of E. suratensis, are unique which involved a

series of events such as pairing, nest making and parental care. The stocked fishes

were found to form schools of 15-20 members and among these, males and females

with specific attributes gets ‘attached’ and a spawning pair is formed, over a

period of several days. ‘Spawning families’ were observed to become established

soon after their introduction into the earthen ponds. The most prominent indication

of the pre mating pair formation was the conspicuous intensification and darkening

of color pattern in males. In the case of females, black spots and blotches appear on

the ventral side between pelvic and anal fins, during spawning period. On the other

hand, among males, the breeding tint is more strongly marked, characterized by a

bluish green iridescence and sparkling pearly white spots. Although E. suratensis is

generally stated to be monomorphic, this brilliant breeding coloration among males

may be considered as a sexual dimorphic feature. Soon after the development of

the breeding hue, paired fishes were found to form isolated territories. The paired

fishes form close, stable and long lasting pair bonds and start breeding in regions

devoid of vegetation. The breeding pair starts swimming along the side of the pond

in search of a suitable substratum for nesting. When they find an appropriate

nesting substratum, 11 to 45 cm raised above the ground, the substratum surface is

cleared off attached algae by browsing them over. The fish is observed to browse

the algal growth by rhythmical jaw movements and the collected algae are sucked

deep in to the mouth by regular suction movements at irregular intervals.

Invariably, the fish prefer spawning surfaces available in shallow waters. The

fishes were also found to utilize any type of stationary object such as coconut

leaves, coconut husk, stones, PVC hose pipes, bricks, coconut roots or any such

hard solids available along the shallow periphery of the pond (Plates 8a – 8h). In

the present trial bamboo stumps planted at close intervals were utilized as nest

substrate. The selection of the nesting site, clearance of the site off vegetation and

cleaning of spawning surface are seen completed in 3-5 days. Both male and

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female partners actively engage in nest preparation. After the substrates are cleared

off, attached algae and even the minutest particles adhering to the surface are

cleared, the male fish begin to excite the female by hitting on the vent and nibbling

on the abdomen and the pair swims around the chosen substratum. During

ovulation, the female lay flat on to the spawning site and gently move from end to

end and begin to attach eggs carefully, with the help of its tubular, fleshy and cup

like ovipositor. The female fish then glue their sticky eggs by pressing closely on to

the nest surface, one by one in a single layer, supported by their ventral fins. After

the extrusion of a few eggs, over the selected site in one or two trial runs, the male

fish following close behind, in swift and rapid movements dashes over the freshly

laid eggs, releases a spray of milt and fertilizes them instantly. After the males

have completed their task, the female repeat the process of egg extrusion on to the

nest surface. And this process of egg laying and fertilization is continued several

times and the eggs are placed closely in a chain, not touching each other. The

whole process of spawning is completed in 45 to 60 minutes. The number of eggs

per brood, in the experimental conditions varied from 250 to 1573 with a mean of

854. Nest area per brood was observed to vary from 20 to 49.5cm2. The nest

preferences and the egg yield are given in Table 5.1. Altogether 91 nests are

observed in the pond during the experimental period of one year. Maximum

breeding intensity was observed during September (31 No.) followed by July (15

No.).

Table 5.1. Egg attachment of Etroplus suratensis in wild (pond)

Sl. No.

Nesting substrate Nest Area cm2

No. of eggs

No./ cm2

Fertilisation %

Hatching %

1 Coconut-petiole 49.5 990 20 70.71 70 2 Coconut-petiole 36.5 730 20 89.0 2 3 Coconut husk 20.0 960 48 100 4 4 Wooden poles 20.3 1215 60 92.2 13 5 Granite block 22.5 260 12 100 48 6 Coconut leaf 43.7 1573 36 100 10 7 Fire brick 22.9 642 28 98.75 32.4 8 Coconut husk 28.26 1243 44 97.58 38.33 9 Hose tube 48.0 250 5 100 33

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The very next day after egg fixing, prior to hatching, the parent fish start

excavating small cup like pits (‘thadam’) on the pond floor (Plate 9), just below the

selected nesting substrate, where the eggs are laid, by scooping out mud and

cleaning the nearby vegetation by vigorous mouth picking movements. The

bottom pits vary in number from 7 to 15. Nursing pits are excavated on firm and

stable ground in clayey bottom and the fish avoid loose and sandy sediments. The

average size of the shallow ‘pit nurseries’ of pearlspot varies from 3-10cm in

diameter and 2-7 cm in depth. Both the couple participates in the process and males

are more actively involved in this laborious job. On an average 12 pits are observed

per brood. The fish was found to prefer a breeding depth ranging from 15 to

44.5cm. (Table 5.2)

Table 5.2. Details of pit nurseries made by Etroplus suratensis in pond breeding

Water column

(cm) Distance between

pits (cm) Diameter of

pits (cm) Depth of pits

(cm) Sl. No.

No. of pits by a pair Range Av. Range Av. Range Av. Range Av.

1 11 19.0-28 23 2.0 - 9 5.82 7.0-10.0 8.5 3-5.5 4.3 2 9 22-26.5 25 2.0 -9 5.42 5.0-7.0 5.79 4.0-6.0 5.0 3 13 15-26 22 4.0-10 7.5 4.0-9.0 6.21 3.0-5.0 4.0 4 15 17-30 24.4 2.0-8.0 3.91 6.0-9.0 6.0 5.4-7.0 6.0 5 13 29.8-37.2 33.78 3.0-17 6.63 3.5-5.5 4.5 2.0-5.0 3.76 6 7 25-30 27.82 4.0-9.0 6.08 4.0-5.0 4.5 3.0-4.5 4.04 7 15 28-44.5 37.73 2.0-12 5.56 3.0-6.0 3.8 3.5-4.2 3.32 8 10 16.5-22.9 18.92 4.0-19 10.43 5.0-10.0 7.24 4.5-5.5 5.0 9 9 28-36 25.83 7.0-13 10.33 4.0-5.0 4.33 3.0-5.0 3.67

10 14 20-32 26.17 3.5-10 7.10 4.0-6.5 5.0 2.0-7.0 4.0 11 15 25-30 27.6 2.0-8.0 5.13 5.0-6.0 5.63 3.0-6.0 4.8 12 13 29-37 33.2 4.0-7.0 5.44 4.0-7.0 5.7 2.0-6.0 3.7 Av. 12 15-44.5 2.0-17 3 - 10 2.0-7.0

In contrast to the spherical shape of the mature eggs in most teleosts, eggs of

Etroplus are ovoid. The extruded eggs are also demersal, and appear as creamy

yellow elliptical bodies, the major(x) and minor (y) axis measuring 2-2.70 mm and

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1.00 mm respectively. The eggs are seen attached to the nest surface by a stalk in a

single clutch with out any overlap. The whole egg mass appear as patches.

Plate.9. Pits of E. suratensis in earthen ponds

The breeding and courtship behaviour in pearlspots can be categorized into

two phases; pre-courtship and post-courtship behaviour. During the pre-courtship

period, the fish exhibits behavioral activities that largely involve display of

nesting substrate and spawning movements including cleaning of the nest site for

egg deposition. During post-spawning phase, the fish largely display behavioral

activities that help to aerate and guard the eggs and the hatchlings from predators.

After the eggs are laid, the eggs are diligently guarded and aerated by the female,

The male guard the territory, and chases away all intruders. The female with their

rhythmic fanning activity by the pectoral fins continually aerate the eggs. The

guarding female occasionally places its mouth gently against the eggs and sucks

away the adhering particles. This process popularly known as ‘mouthing’ helps to

clean the eggs, a behavior characteristic to substrate guarding cichlids. The eggs

hatches out, generally in 70-72 hours, the newly

hatched hatchlings or ‘wrigglers’ are picked

up by the brooding female in its mouth and are

transferred to the breeding pits on the shallow

pond bottom. As the hatchlings are fully

transferred, the female actively engages in ‘pit

guarding’ and closely care the deposited young

ones in the pits (Plate 10). During this period, Plate 10. Joint parental care

‘pit guarding’

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the parent fish continue fanning of pits with their fins and render oxygenation of the

hatchlings that are sheltered in the pits. During the wriggler stage also, fanning

and mouthing of the brood is continued. Occasionally, a few wrigglers are picked

up by the parents, rolled out in the mouth and returned and some times, the entire

brood of wrigglers are shifted from pit to pit. This process of pit transfer probably

helps to cleanse the sticky larvae by removing the adhering particulate matter.

As the yolk is fully utilized, with in a week, the wrigglers develop their

locomotor abilities and become free swimming and the larvae gradually move out

of the pits, in schools and swim freely in to the open waters, escorted by both the

parents. During this period, the movement of the larvae is largely limited with in

the territorial limits, the young ones when disturbed, are seen returning to the pit

nurseries. Even after the brood reaches free swimming stage, parental protection and

constant vigilance is continued and parent fish continue to attack the potential

predators. Individual fry that stray from the brood are orally retrieved by the parent

and brought back with the others. The parents communicate with the young through

signaling by jolting movements and ‘fin flicking’. The fry respond spontaneously

to this ‘calling behavior’. The parental patronage is continued for about two months

till the young ones scatter out and move freely in search of particulate food

materials.

5.2.3. Captive Breeding of Etroplus Suratensis

As E. suratensis was observed to exhibit such a complex and unique

courtship behaviour, involving pairing, nesting and parental care, captive breeding

of Etroplus suratensis was undertaken, in specially designed artificial raceway

tank provided with simulated natural conditions. The raceway system was devised

as a trapezoidal tank with slopping sides and bottom (Plate 11). The tank

facilitated appropriate and diverse depth situations ranging from 30 to 80 cm. This

system was provided with continuous water exchange that facilitated manipulation

of the breeding environment in terms of temperature regime, turbidity, and a mild

flow. Artificial spawning surfaces, comprising 30-35cm long casuarina poles (25

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nos.) fixed on specially fabricated cement concrete base were placed vertically in

the tanks, approximately 50 cm away from the tank margin at varying depths. The

distance between spawning surfaces were approximately 1 meter, taking in to

consideration the territorial requirements of the species. In the very steep and

sloping margins of the tank, where casuarina poles could not be erected vertically,

bricks and cement concrete sinkers, 8-10 numbers were also placed as nesting

substrate Prefabricated artificial pits measuring 6 cm diameter and 4 cm deep were

also deposited close to the nest substrates to facilitate ‘pit caring’, characteristic to

the species (Plate 12). Selected brood fishes, 70 pairs, of size 15cm (90g) to 23cm

(250g) were placed in the raceway tanks, filled with filtered lake water. In order to

prevent formation of algal blooms and to avoid turbidity, the raceway tank was

provided with adequate shading from above by using 50 percent shade netting.

5.2.3.1. Maturation Assessment and Selection of Brooders

In order to enable natural pairing, captive stocks of male and female

broodfish raised in the holding ponds were stocked in the breeding raceways at 1:1

ratio by number. Paired fishes in the broodstock pond were also picked up and

transferred. Fishes were selected based on their external secondary sexual

characters, which were prominent during the breeding season. Ripe and gravid pre

spawning females were identified by its enlarged, reddish and swollen genital

papillae, which is modified in to a fleshy ovipositor. Since milt was not expressible

from the males, they were identified by their thin and pointed genital papillae and

peculiar coloration. Color differences among males were marked during mating

time. Males appear brilliantly colored, and pigmentation of the males begins to

intensify as nest construction commences. Apparently female mate choice appears

to be correlated with this male coloration. In sexually motivated males, as a

common pattern during courting, black occipital stripes were found to appear

between the eye and opercular spot. The swollen cup like ovipositor/ genital

papillae in females and intense display of pigmentation among males during

courting period can be considered as the ‘on heat’ signs of male and female

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fishes (Plate 13). Such paired fishes were seined out from the holding ponds,

assessed of their maturity and stocked in the raceway system for breeding.

Shortly after release, the fishes were found to form 2-3 groups as observed in

the pond breeding trials. Breeding pairs were formed invariably from members with

in the groups and after pairing, the pair gets separated from rest of the group and the

pair was found to search for the nesting substratum at shallow water depths.

Presence of adequate number of spawning surfaces was observed to enhance pair

formation.

5.2.3.2. Nest building and care of young

Pair bonding among the mates was almost stable and not momentary.

Apparently, mate selection was guided by some specific attributes characteristic

among members within a group. In order to enhance pair formation among the left

over members and find choice pairs of appropriate attributes, it was felt necessary to

increase the size of the groups. For this additional numbers of fishes in readiness to

breed were collected from the holding ponds and added to the breeding tanks at

periodic intervals. The paired mates released were observed to clear off algal growth

from the nesting substrate, by browsing with their truncated cone like snout. The

modified mouth also helped in suction feeding. The female fish was found to probe

the artificial nesting substrates with the genital papillae and spontaneously spawn

with one or two trial runs, using the modified cup like ovipositor. At this point of

time, the male and female positions parallelly one behind the other, lay flat to the

spawning surface and then began to attach their adhesive eggs on to the substrate.

After the female has completed attaching one or two rows of eggs, the male

following close behind spontaneously hover over the egg mass, deposited by the

female and fertilizes the eggs by sprinkling milt over the egg patches. Duration of

sperm motility was found to vary from 3 to 4 min. Eggs are never laid on top of

other eggs but are concentrated in a single layer so that one egg just touched the

other (Plate 14). Video graphic recordings of the courtship behaviour and spawning

sequences (Plates 15a – 15h) indicated that the orientation of the spawning partners

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one to the other was characteristic. During spawning, the partners assumed a

ritualistic side-by-side position. Body contact between male and female fish

occurred only infrequently and incidentally as it did not appear to serve any

particular function. The water temperature during courting and breeding varied from

25-270C .

In all, 50 nests were made by the stocked fishes, within the raceway system

during the experimental period of 12 months, during 2004-05. Over 75 percent of

the nest were confined to shallow clear areas at depths between 12 and 45cm. The

maximum depth selected for nest formation with in the raceway was 53.5cm. The

breeding performance of E. suratensis in the artificial raceway system is

summarized in Table 5.3. In the tank breeding system, the percentage success of

breeding was as high as 71 percent, much higher than earthen pond system.

Evidently, the fish was found to exhibit a perceptible preference to cement concrete

substrates as compared to other materials. The mean number of eggs within a nest

was observed to be 32 per cm2. The patch size of eggs per nest was found to vary

from 18 to 56cm2 (Plates 16a – 16h). The number of eggs released per spawning

ranged from 382 to 1966 with a mean of 830. The number of eggs varied according

to the size of the fish and a female fish of average size, 100g was observed to lay

around 250 eggs, where as a female fish of size 200-300g produced more than

1000 eggs. The breeding intensity was however, higher under earthen pond

situations where increased mate choices were available as compared to artificial

tank conditions. The fertilization rate in the confined raceway system fluctuated

between 82.3 to 100 percent.

Egg incubation and hatching could be achieved in two ways, (1) with in the

breeding tank ensuring care of the breeding pairs and (2) in separate larval rearing

tanks with out parental care. For egg incubation, the ‘nest’ along with the eggs were

‘robbed’ from the females, and immediately transferred to indoor incubation tanks,

each of 1.1 t capacity provided with continuous aeration. When the parent fishes

were allowed to care the eggs, the fish was observed to places its mouth gently

against the eggs and was seen to suck away loose particles. The fanning parent

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holds position close to the clutch and facilitated water movement in high amplitude

by their ritualistic pectoral fin beats.

Table 5.3. Egg attachment of Etroplus suratensis in raceway systems

Sl.No. Nesting substrate

Nest Area cm2

No. of eggs

No./ cm2 Fertilisation %

Hatching %

1 Earthen pots 56 951 17 75.7 90* 2 CC. substrate** 32 851 27 90 # 3 CC. substrate 52.5 1371 26 90 # 4 CC. substrate 32 420 13 100 63* 5 Wooden poles 18 792 44 82.32 20* 6 Wooden poles 37.8 1966 52 98 29* 7 Hose tube 19 382 20 100 99 8 Fire brick 18.3 439 24 100 # 9 CC. substrate 18 633 35 95 63

10 CC. substrate 54.4 390 7 98 90 11 CC. substrate 27 1350 50 98.7 34* 12 CC. substrate 28 477 17 95.8 65

* incubation inside the laboratory # eggs are removed by the parents

** Cement concrete substrate

When eggs were incubated separately, without parental patronage, hatching

of eggs occurred in 70-72 hrs under a temperature regime of 25-27oC. The

hatching was protracted and the whole brood was observed to hatch out in a long

interval of 24 to 26 hrs after the first hatching. Embryonic development, hatching

and larval development stages, captured in a Magnus Imaging System connected to

a computer monitor is given in Plate 17 and 18 a-c. The hatched out larvae, or the

‘wrigglers’, were heavily yolked and observed to sink to the bottom. They were

found to instinctively congregate on the tank floor. In the tank incubation,

involving parent fishes, fanning and mouthing of the brood were continued. During

parental care, the fish responded even to the slightest disturbance and was found to

remove all the eggs away from the substratum when bothered. Eggs were also

removed at times when the water became more turbid. Parents continued to

maintain a constant current of water over the pits by fanning with their fins and was

found to clear off any adhering foreign particles on to the larval body.

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Both parents were found to take turns at guarding and fanning them. When

eggs were incubated in spawning tank under parental care i.e., when the brood

fishes were left undisturbed along with eggs , hatching rate varied from 63 to 99

percent, while in artificial incubation without parental care, ie., eggs robbed from

the parents and incubated artificially, the hatching rate was found to range from 20

to 90 percent.

A comparison of the fry yield under artificial tank breeding and natural

breeding in earthern pond condition revealed that fry yield under tank breeding is

perceptibly high,(mean yield 20 to 99 percent), as compared to earthern pond

system (2-70 percent). Under the tank breeding system, a total of up to 2375

hatchlings were obtained from a single brood and this was apparently very close to

the fecundity of the species.

5.2.3.3. Egg Incubation in Larval Rearing Tanks

In situations when eggs were removed from the parents and separately

incubated in Larval Rearing Tanks (LRT), the eggs were found to become

increasingly infected with fungal elements. However, when parents were also

transferred to the larval rearing tanks, in the assumption that they will take care of

the transferred brood, curiously, the fish was found to prey on their eggs. Such a

behaviour was noticed even in the raceway breeding tanks, when the brood was

disturbed, the parent fish was observed to devour the developing eggs. On the

contrary, when the eggs were retained undisturbed for hatching ensuring care by

parents, the parent fishes were found to continually pick up the eggs in their

mouth, destroying the dead and infected eggs especially those that are attacked by

fungus.

Brooding males were more aggressive and were found to push and strike

the intruders using their body or caudal fin, through rapid jerking movements. The

guarding males defended the nest from other fishes and at times, strike the intruders

with its head. And during such ‘head butts’ males strike its intruder on the flanks,

most often dislodging the scales from the opponent(Plate 19). Some times, two

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males may also engage in fight, head to head. At this time, their coloration was

found to intensify markedly.

5.2.4. Embryonic Development

The eggs of E. suratensis, is elliptical in shape, with an average length of

2.2mm and width of 1mm. Like other substrate brooding cichlids, the eggs remain

cemented to the nesting object by a stalk. Eggs of Etroplus are pale yellow in

colour and after fertilization the color changes slowly and they become brownish

just prior to hatching. Cell division in E. suratensis eggs were found to be very

slow, probably due to the presence of large amount of yolk (Plate 17). After 1hr of

fertilization, a blastodisc readily become recognizable on the anterior side of the

yolk. The cleavage is restricted to the animal pole region. The first cleavage is

initiated at 1.30hrs resulting in the formation of two blastomeres of equal size. The

second cleavage results in four equal blastomeres at 2hrs, and the third division

results in 8 blastomeres of equal size followed by the fourth division leading to

sixteen celled stage, at 4 hrs. At this stage, the cells appear irregular in size. Further

division results in thirty two celled stage at 4.30 hrs and from this time onwards the

cell division is no more equal. Cell boundaries are clear, while the cells appear

more or less crowded and occupy the whole space in two layers.

The sixth cleavage results in the formation of 64 celled stage and at 7.30hrs

a multilayered blastula is formed. By 12 hrs, the blastomeres appear as a mass of

cells above the yolk mass. Gradually, the cells spread over the yolk, moving

towards the vegetal pole. As epiboly progresses, the blastoderm at the animal pole

thins out and extend on to either side of the yolk. The yolk mass at this stage

bulges out into the animal pole and the blastoderm appear as a transparent

crescentic mass which is the first sign of formation of embryonic membrane. The

gastrulation commences at about 18 hrs. The germinal ring become differentiated at

this point of time and by 21 hrs, the germ ring invade and migrate towards the

equator of the yolk. The extension of the germinal ring is gradual and slow owing

to the enormous quantity of yolk present.

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By 24.30 hrs, almost 50 percent of the yolk becomes covered by the

developing cells. At this stage, a thin layer of cells were found to envelop the yolk.

By 30 hrs, the anterior region of the embryo expands and the neural plate, appear as

a layer dorsally at the axial end. A thickened median ridge also grows downwards

along one side enveloping the yolk. By 33.30 hrs, head fold appears and the embryo

extends from the anterior end as an elongated tube. The cephalic end of the embryo

gradually gets lifted up and optic buds become visible. At this point of time, somites

gradually become recognizable. Rudiment of heart appears, at about 38-40 hrs and

rhythmic movement of the heart become visible. At 41 hrs, the cerebral region

become differentiated and at the cephalic end otic capsules also become

conspicuous. At 42 hrs, pumping of the two lobed transparent heart, ventral to the

cephalic end become conspicuous and the beats could be counted as 86 per minute.

At this stage 22 pairs of somites are clearly visible. Head and tail is more distinct,

projecting distinctly and the embryo covers almost 50 percent of the yolk at this

point of time. By 43 hrs, cerebral vesicles become clear and heart beat become

more rapid. Blood streaming to the tail region is clearly visible at 49 hrs and the

embryo begins twitching at irregular intervals. By 52 hrs, the tail becomes free

and by 54 hrs, the eye becomes enlarged and prominent. Embryo at this time

encircles almost 60 percent of the yolk and become ‘C’ shaped. The embryo also

exhibit wriggling movements at times within the egg case. By 60 hrs, the embryo

covers almost 80 percent of the yolk and the to and fro streaming of blood become

conspicuous. By 64th hr embryo appear to encircle over 90 percent of the yolk.

Heart beats become rapid and regular, at beat count, 128 per minute. The embryo

completely encircles the yolk by 66 hrs. Prior to hatching, tilting and wriggling

movement of the embryo become more frequent. Gradually the embryo wriggles

violently inside the egg case. The egg case become thinner and it ruptures dorsally

at the cephalic end. Hatching occurs at 73 hrs and the tail emerges out first. The

embryo remain quite for sometime, within the broken egg shell and with the

lashing and wriggling of embryonic movements, the opening get widened. During

further development, the yolk become transparent and stellate chromatophores and

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the oil globules become visible. At 78 hrs, the heart beat become more rhythmic

and rapid, and beat at 138 per minute. Slowly, the membrane near the head also

gets separated and the hatchling becomes free from the shell membrane by 75-80

hrs. This process of hatching is protracted i.e. time interval between the rupture of

egg membrane and emergence of hatchling is quite long. Hatching of eggs in one

brood is also protracted and is completed only in 24-26 hrs. All the developmental

stages of the egg are summarized in Table.4

Although natural breeding of Etroplus has been indicated to be linked to

lunar cycle, such a correlation was not evident in controlled raceway system.

However, spawning frequency was highest during quarters close to new moon phase

from dwadashi to chathurdasi in the tank conditions. This lunar periodicity was

however more perceptible in earthen pond system.

Table 5.4. Embryonic development in Etroplus suratensis

Time after fertilisation

Developmental stages of eggs

1.00 Blastodisc appears 1.30 Two blastomeres 2.00 Four blastomeres 4.00 Blastula appears

10.00 Transparent crescent shaped blastula 18.00 Germ ring is conspicuous 38.00 Heart beating starts 42.00 Head and tail region become more conspicuous 46.00 Cerebral vesicles are clear 48.00 Twitching movement starts 52.00 Tail become free 54.00 Eye auditory vesicles more conspicuous 64.00 Embryo encircles 90% of the yolk;

Head region more prominent 73.00 Egg membrane breaks 80.00 Hatching

As the yolk gets absorbed and the pectoral fins become active in 5-6 days,

the young become free-swimming and the parents lead them out to the open waters.

The family unit moves about slowly guarded by parents and the fry begin to feed on

food particles on or near the substrate. The turbulations on the tank bottom created

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by the parent fish by their fin movement appeared to help in making available

suspended particles as food to the young ones. The high fry yield under protracted

parental care is apparently linked to increased availability of particulate feed and for

the young.

5.2.5. Larval And Post Larval Development

5.2.5.1. Newly hatched larva

Newly hatched E. suratensis larvae is approximately 4.5 mm in size. The

yolk is voluminous with large oil globules and the larvae being heavy sinks to the

bottom. Yolk sac is ovoid and is enormous; broader at the proximal end and narrow

towards the distal end and the yolk extends almost upto the anal opening. The

hatchling is characterized by large pigmented eyes and olfactory pits. Mouth and

jaws are not fully developed at this stage. Anal opening is seen located 4-5 somites

below the level of yolk sac. Fin fold appear continuous from 3rd somite dorsally,

seen attached upto the yolksac on the ventral side. Heart is prominent and is seen

pulsating, located between the head and yolksac, ventral to the eyes. Caudal

circulation through dorsal and ventral blood vessels and interconnecting canals is

conspicuous, and is visible through the transparent body. Notochord and myotomes

are clear, with little ossification in the skeleton. A full complement of fins is also

absent. The newly hatched larvae congregate in pits and bottom corners of the

larval rearing tank, head down and tail up with lashing movements and apparently

exhibit positive geotaxis and a negative phototaxis.

5.2.5.2. Hatchling – 2 day old

In about 24 hrs after hatching, the larva attains an average length of 5.0 mm

(Plate 18a). Yolk sac that remain attached to the head region of the larvae become

separated and the head appear free from the yolk mass. The yolk sac becomes

gradually reduced and large eyes appear deeply pigmented. Otolith is clearly visible

within the transparent body. The two chambered heart located ventrally anterior to

the globular yolk is observed to pulsate vigorously at 99 beats per minute. Mouth

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cleft appears during this period, although not with any marked mobility. At this

stage, blood circulation is rapid and continuous, discernable through the transparent

body. Dorsal fin fold also appears continuous through the caudal end.

5.2.5.3. Hatchling – 3 day old

The larvae measures 6.0mm in length on the 3rd day(Plate 18b). Head region

is well developed with the formation of a characteristic spout like mouth. Lower

jaw begin to exhibit rapid movements. Yolk sac become reduced to half its size and

heart appear spherical with rapid pulsation. The transparent body becomes

pigmented gradually.

5.2.5.4. Hatchling – 4 day old

The larvae measures 6.0mm in length on day 4, starts gliding on the bottom

and begins to swim up with yolk sac down (Plate 18d). Pigmentation become

remarkable on the head and trunk region. Alimentary canal becomes visible through

the body, marked by intermittent pulsative movements. Gradually yolk mass

decreases in size. Upper and lower jaw becomes well developed with characteristic

jaw movements. At this stage, the young ones are found to congregate inside the

artificial pits. Since the fins are not functional, larvae are seen to creep around the

tank bottom to form gregarious patches.

5.2.5.5. Hatchling – 5 day old

The larva attains a length of 6.5mm on fifth day (Plate 18c). The yolksac is

greatly reduced at this time. Fin rays in the caudal region become conspicuous and

the fin fold appear continuous.

5.2.5.6. Hatchling – 6 day old

The larva measures 6.5mm and the yolk sac is almost resorbed by the 6th

day. Pectoral fins also begin to appear at this period. Fin rays become conspicuous

throughout the length of the fin fold. Operculum also becomes conspicuous and the

gills become functional. When kept in glass tank, inside the laboratory, the young

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ones are seen to congregate near the aeration points and are found to move in

swarms.

The fry become free swimming on the 6th day and move in shoals guided by

the parents, swimming mostly underneath the parents. The yolk gets fully resorbed

by this time and the hatchlings attain an average size of 7-8 mm.

5.2.5.7. Nursing of hatchlings

The larvae, after the resorption of yolk, begin to feed on particulate food

matter. They feed on the food particles kept in suspension probably by the

bioturbulation or fin digging activity of the parent fish, in natural pond bottom. The

characteristic vertical bands on the hatchling appear on the body when the

hatchlings attain a size of approximately 1.5cm. In the fry nursing tanks, the young

ones attains a size of about 20mm in one month and freely feed on zooplankton and

powdered Higashi-Fresh (Protein 20 percent). The larvae attain a juvenile size of

3- 3.5cm, in two months of nursery rearing (Plate 20). The juveniles during this

stage is characterized by a black spot on the dorsal fin which gradually disappears as

they attain fingerling size of 4.5- 5cm .

The fry accepts supplementary feeds comprising ground nut oil cake, rice

bran and commercial feed pellets. The young ones now begin to feed on

filamentous algae on the submerged bamboo poles fixed at close intervals in the

nursery system.

5.3. Discussion

E. suratensis, a cichlid endemic to the region, is one of the most potential

candidate species for aquaculture with immense commercial possibilities.

Popularization of farming of this species calls for standardized methods for seed

production. With its opportunistic ability to feed on a variety of alternative food

resources, cichlids are considered extensively adapted to trophic specializations.

However, as observed in this study, it is most conservative with regard to breeding

behavior. As the fish display complex breeding habits and parental behavior,

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traditional methods of breeding inducement by hormonal manipulation has not been

effective.

5.3.1. Pond breeding of E. suratensis

Placement of brood stock in open ponds and pond spawning has been the

only method of seed production of E. suratensis, followed for long.

Investigations on captive breeding of this species under controlled conditions by

manipulation of the breeding environment revealed that in this species, breeding is

preceded by a very complex pair bonding. Fecundity of this species being low, the

actual yield of hatchlings per brood also has been very poor. The realized

fecundity has not been more than half of the potential fecundity. The sperm motility

is higher i.e. 3-4 minute in E. suratensis. Nikolskii (1963) observed that the

duration of sperm motility is higher in slow flowing waters, than fast flowing

situations (i.e. 10-15 sec.).

Although, the breeding biology of the fish with regard to incidence of

gravid females and gonad maturation indicated that the major spawning season of

E. suratensis in Vembanad Lake is from February-April and June-October, the fish

could be made to breed round the year under captive conditions. Nevertheless, in

controlled breeding system also, maximum spawning success is achieved during

June-September. In the artificial raceway system also, apparently, the fish was

found to breed profusely in conditions of low turbidity, facilitated through periodic

water replacement.

5.3.1.1. Decreased turbidity favour visual displays

Visual contact between the parents and the offsprings appear to be a critical

requirement for spawning of E. suratensis (Breder and Rosen, 1966; Keenleyside,

1979; Blumer, 1982; Gross and Sargent, 1985). On the basis of the intensity of nest

building, Ward and Samarakoon (1981) observed that E. suratensis in coastal

lagoons of Sri Lanka breeds during two periods in a year, when the salinity is high

and turbidity is minimal. These authors therefore inferred that fast flowing murky

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waters are inimical to survival of E. suratensis. It appears that the silt laden murky

waters and heavy river discharges during monsoon apparently restrict visual

signaling and threatens the survival of young. In Kerala backwaters, E. suratensis

is reported to exhibit intense spawning during November-March with a peak during

December-January (Jayaprakas,1980; Krishnan and Diwan,1990). This should be

linked to high transparency of water with the cessation of monsoon and incursion of

saline waters. It may be inferred that pearlspots prefer water conditions and

situations that ensured visual contact with the young for breeding. Jalabert and

Zohar (1982) also observed that visual stimuli hastens ovulation but with little

influence on oogenesis. Cole and Ward (1969) also observed that visual displays are

important in the parental behavior of chromides. In terms of selection of nest sites

or selection of mates also, visual displays might be apparently important and it is

presumed that clean water favour this behaviour.

Ward and Samarakoon (1981) observed that E. suratensis reproduced twice

during the year when water conditions were favorable for nest construction and

maintaining visual contact with offspring. These authors have also indicated

decreased water turbidity and increasing salinity as two important factors that favor

spawning. Samarakoon (1983) observed that readiness of the fish to breed is

dependent not only on conditions of turbidity but also on current speed. De Silva et

al.(1984) also presumed that E. suratensis is a visual feeder and so they preferred

clear water for breeding, probably because this ensured feed availability for the

young ones.

5.3.1.2. Shallow water conditions

In Chilka lake, Kowtal (1976) observed that E. suratensis breeds round the

year with peaks in summer and winter, when favorable condition becomes available.

Jhingran (1991) reported that in shallow confined waters, the fish breed almost

round the year, while in backwaters, the fish breeds twice a year. Apparently, the

response of fishes in confined condition is at variance from natural systems and

Fryer and Iles (1972) cited a number of examples to signify that fishes in confined

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conditions might breed more frequently and at a smaller size than natural

conditions.

5.3.2. Artificial raceways and simulated situations

In the raceway system devised, under simulated environment,

E. suratensis could be stimulated to spawn round the year. Rapid removal of eggs

and young ones from the breeding tanks and rearing them in separate systems,

possibly have reduced parental care period. Lee (1979) observed that parental care

suppresses expression of full reproductive potential and fry removal shortens the

time interval between spawning. The present observations on round the year

spawning under controlled raceway systems support the hypothesis that removal of

brood from the caring parent can help to reduce the spawning interval. Peters

(1983) found that the average time period between spawning in tilapias can be

shortened by removal of freshly spawned hatchlings. Verdegem and McGinty

(1987) also indicated that frequent removal of incubating eggs in O.niloticus is one

method that increase spawning frequency and fry production.

In the present study, under controlled conditions in sloping raceway system

E. suratensis was found to prefer breeding in shallow depths. In nature, although

the fish is reported to be eurytopic, and occupy a variety of different habitats;

nursing of juveniles is accomplished in shallow fringe regions, while the maturing

ones move progressively to deeper waters. Ward and Samarakoon (1981) also

observed that E. suratensis migrate to shallow water for breeding. Ward & Wyman

(1975) made a similar observation that sub littoral regions, close to the marginal

vegetation is the habitat of the young ones. Ward and Samarakoon (1981) observed

that unlike E. maculatus that select regions rich in vegetation, E. suratensis select

more specific regions in open locations devoid of vegetation, as nest site. While

E. maculatus breed in several patches in vegetation rich areas, E. suratensis select

bare areas fringed with vegetation. Although parents and nests are exposed in such

open locations exposing them to predation, detection of predator appears to be better

facilitated in such situations. The observation on the abundance of young ones and

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the breeding ones in the shallow littoral regions and fish of larger size in the deeper

regions (Winn, 1956), indicates that conservation management of pearlspot calls for

more co-ordinated approaches concentrated in shallow waters, the natural breeding

habitats of the species.

5.3.3. Artificial spawning substrates

The higher rate of spawning in the artificial raceway system is invariably

linked to increased availability of artificial nests substrates provided with in the

tanks. In fact, an upsurge in spawning frequency was observed when spawning

surfaces were supplied. However, the artificial, pre fabricated breeding pits

provided were seldom utilized by the parent fish. The fish rather preferred to utilize

the cleaned floor of the tank for hatchling care. Occurrence of large schools of fry

containing many more individuals than a typical single brood, is indicative of the

communal care behaviour in E. suratensis as observed also by Ward and Wyman

(1975, 1977). E. suratensis has been reported to prefer a variety of nest substrates

in natural pond situations viz., stones, coconut shells, coconut petioles, tiles, bamboo

and wooden pieces. Samarakoon (1985) observed that E. suratensis spawned rapidly

in ponds supplied with spawning surfaces as compared to situations without

appropriate breeding substrates, when similar environments were provided. Sultana

et al., (1995) also stated that in nature, the fish spawn on a variety of hard objects

that facilitate attachment of eggs and this include stones, pieces of wood, coconut

husks, water logged coconuts, mid ribs of coconut and palm leaves tiles, bamboo

pieces, asbestos sheets, and any other submerged objects situated at a depth not

more than 100 cm. A sticky material produced at the time of ovulation by the

granulosa, around the special threads emerging from the zona radiata has been

indicated to glues the eggs into the substrates (Nicholls and Maple, 1972).

Incidentally, the spawning fecundity was quite high for fishes bred in tank

breeding trials as compared natural system. This is apparently due to the better

nutrition of the broodfish raised under captive conditions, as the number of eggs

released per spawning naturally increases with body weight and physical well being

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of the fish. Food availability and feeding intensity has been reported to influence

rapid maturation of gonads ( Sobhana and Nair,1980)

5.3.4. Spawning rhythm and lunar periodicity

In most teleosts, spawning periods appear to be adjusted to environmental

factors such as photoperiod, temperature, salinity, rainfall etc so that they are

suitable for rearing offspring. Avault (2006) has described key factors that

stimulate, inhibit or exert regulation on various stages of breeding cycle. In

temperate zones, where photoperiod and temperature are of greater magnitude,

spawning occur during limited period in a year. In tropical regions, temperature is

rarely the limiting factor, the effect of seasonal rainfall is most apparent.

Breeding of E. suratensis appeared to be linked to the lunar cycle and over

30 percent of the breeding occurred during dwadashi to chathurdashi. Probably,

this is a physiological adaptation. Being an estuarine fish though adapted to thrive

in freshwaters, the tidal amplitude facilitated by the lunar phase provided stable

conditions for ovulation as well as egg care. Lam (1983) indicated that in many of

the tropical fishes, peak spawning activity is often associated with lunar cycle,

rainfall or floods. Mathew et al. (2002) observed that in case of Groupers,

Epinephalus tauvina spontaneous spawning occurred 3-4 days before or after the

new moon phase. Sundararaj and Krishnamurthy (1975) reported that abundance of

zooplankton favored seasonal reproduction of E. suratensis and in Vellar estuary,

South India, such a situation of higher food availability occurring at salinity ranging

from 10-31 ppt coincided with peak breeding.

5.3.5. Coloration and reproductive readiness

As observed in the present study, several authors have indicated that male

coloration intensifies during courtship (Greenwood, 1974; Fryer, 1977; Fryer and

Iles, 1972). Colour patterns are a very important channel for communication in

cichlids (Nelissen, 1991) and this is attributed as an important component of the

specific mate recognition system in cichlids (Ribbink, 1990). Anatomical and

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physiological evidence also strongly suggests that cichlids have strong color vision

(Muntz, 1976). Similar to pearlspots, Rothbard and Pruginin (1975) observed that

during period of courtship, tilapia displays highly intensified body pigmentation

much stronger and more typical among males. McElroy and Kornfield (1990) stated

that the breeding coloration among males is an adaptive mechanism to advertise its

presence and reproductive readiness. Endler (1995) suggested that physical

attributes of habitat, light condition, water clarity etc affect considerably the

expression of male secondary sexual traits and the female enticement and

preferences for these traits apparently influence pairing process. This obviously

elucidates the importance of physical environment in triggering breeding.

Ward and Wyman(1977) and Yamaoka(1991) observed that the nesting of

green chromides is influenced not only by the availability of spawning sites but also

lack of incidence of orange chromides, their major predators that raid and prey on

their eggs. In nature, the obvious predators or cannibals of pearl spots have been

identified to be orange chromides (Ward and Wyman, 1977) as schools of adult

orange chromides raid the nesting locations of pearlspot. In the tank breeding, the

total protection from such predators apparently ensured higher survival.

5.3.6.Territoriality and spawning

In the raceway system devised, the fish was observed to utilize artificial

substrate with in specific territories and at specific distance. Samarakoon (1981)

also observed that E. suratensis breed in isolated territories of approximately 2m in

diameter. And hence, it is reasonable to suggest that spawning surfaces should be

placed at interval of 2-4m to ensure the required degree of isolation and encourage

nesting. Despite closer spacing of the substrates in the raceway system, nesting

occurred only at a wider space interval. This apparently highlights the territoriality

of the species.

The percentage success of breeding was quite high at 71 percent in the

raceway breeding system. It appears that the probability of bringing together male

and female fish with attributes necessary for successful pairing is enhanced in

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controlled tank breeding, where the group size of broodstock is considerably

increased. Samarakoon (1985) observed that when E. suratensis is stocked in a sex

ratio @ 1:1 under earthen pond system, less than one third of the fishes were found

to breed. It was also observed that pair formation and nest site selection occurs only

within groups, and among members of a groups less than 50 percent succeed in

pairing. Legendre and Trebaol (1996) observed that in case of mouth breeding

cichlids S. melanotheron, spawning interval is considerably increased when sex

ratio is in favor of females which implies that higher sex ratio does not significantly

increase individual spawning frequency.

5.3.7. Tank breeding with Parental patronage

One of the problems encountered in the traditional pond breeding of

pearlspot by environmental manipulation has been the lower yield of seeds in such

systems. And the most serious practical difficulty encountered in this method is

capturing of the juveniles. As the juveniles sink to the bottom, pond draining

becomes inevitable. Such exhaustive collections also bring about unwanted

disturbances to other pair bonded brooders. This difficulty is overcome in

controlled raceway systems where seed recovery is facilitated with less effort.

In tank incubation, with out parental patronage, egg masses were exposed

to fungal menace more often. Some times, heavy infestation with fungal mat

resulted in large scale mortality of eggs. Egg masses cared by the parents were

infected with aquatic fungi less frequently. Takahashi et al. (2004) observed that

under conditions of low parental care, infections are characteristic in large broods.

Bergmann (1968) observed that egg guarding fishes facilitated cleaning of

guarding eggs by two unique cleaning process viz., ‘mouthing’ and ‘snapping’. In

mouthing, the parent fish places its mouth gently against the eggs and sucks away

loose particles. Dead or fungus ridden eggs are removed by a more vigorous mouth

contact, often called ‘snapping’. However, when the brood was disturbed, the

parent fish was found to devour the developing eggs. Fryer (1959), Fryer and Iles

(1972), Holzberg (1978), Ribbink et al., (1980,1981,1983) have postulated that all

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cichlids regardless of their trophic specializations, even most specialized herbivores,

opportunistically prey upon their eggs and embryos if given a chance to do so. Fox

(1975) while reviewing cannibalism stated that increasing population density

coupled with food scarcity are factors that encourage cannibalism.

In the present study also, a more synchronized hatching was apparent when

egg hatching was facilitated by parental patronage. Obviously, parental guarding

accelerated and synchronised hatching and this was well facilitated by mouthing and

nibbling of the eggs by the parents. Zoran and Ward (1983) also observed that in

E.maculatus the embryos kept without parents hatch later, and over a more extended

interval, than those attended by parents.

5.3.7.1. Substrate brooding to mouth brooding among cichlids

Pearlspots were found to spend 68-77 percent of the time budget for

guarding nest and 6-10 percent of their time in interaction with intruders. In

E. maculatus, where the male and female parent alternately cared the young this

time allocation is only half (Ward and Samarakoon, 1981). Cichlids are unique in

their mating behavior and the prolonged period of active parental care of the young

is a characteristic feature. They also guard their offspring for several weeks even

after hatching. In E. suratensis, parental care starts from fertilization onwards and

both parents are actively involved in this process. The parent fish, mostly female,

brood over the fertilized eggs and facilitate an environment suitable for their normal

growth and development. Such a prolonged and close association between parents

and offspring also acts as a two-way communication between generations (Breder

and Rosen, 1966; Keenleyside, 1979; Blumer, 1982; Gross and Sargent, 1985).

Nevertheless, in E. suratensis, both the parents were actively involved in parental

care and nest guarding. Biparental guarding is considered a primitive pattern of

parental care as compared to mouth breeding form of parental care seen among

Tilapias. Oppenheimer (1970) elucidated that mouth breeding syndrome is a highly

derived form of parental care. This behaviour is derived from an ancestral substrate

brooding form, in which parental acts such as mouthing of eggs and transferring of

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the embryos were incorporated. Perrone and Zaret (1979) concluded that biparental

care is a serious evolutionary problem, because in terms of investment, both parents

are not required to raise a brood. However, according to Perrone and Zaret (1979),

the biparental care is an adaptation necessary for survival as this would permit

parents to go foraging alternatively and this would help to keep them in good

physical health for future guard duty. Baylis (1981), while tracing the evolution of

parental care in fishes observed that the major factors that favour parental

behaviour are 1)defense of nest site 2)facility for multiple spawning 3) preservation

of optimal quality of the nesting site and 4) pre-spawning care of hatching eggs.

Noakes and Balon (1982) characterized fish species in to two categories, ‘r

selected’ strategists with a life history pattern that include short growth interval,

early maturation, high fecundity, reduced parental care and short life span and ‘K

selected’ strategists when these species have a prolonged growth interval, deferred

maturation, reduced fecundity, increased parental care and extended life span.

Noakes (1981) observed that ‘K selected’ condition similar to that of Pearlspots is

a more mature and competitive condition, evolved through ecological succession.

Growns (2004) on the other hand classified fishes with a breeding strategy that

involve parental care that ensures protection of young and therefore lower

mortality rates among young ones falling under Guild C. Apparently E. suratensis

with characteristic parental care, nest building and protection of young can be

categorized to include in this category.

5.3.7.2. Parental care behaviour

Fanning is the most common parental care behavior carried out by the

substrate brooders (Keenleyside,1991). The fanning parent holds position close to

the clutch and moves the water with large amplitude beats of the pectoral fins.

Fanning is reported to not only prevent dirt settling but also increase the oxygen

level of water near the eggs. The current of water created over the eggs helps to

remove metabolic wastes. According to Zoran and Ward (1983), both active and

passive fanning are observed in most substrate brooders such as E. maculatus,

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Herotilapia multispinosa etc. (Baylis, 1974; Smith-Grayton and Keenleyside,

1978).

5.3.7.3. Pit caring

Despite deposition of artificial pits, in the raceway system the parent fish

was observed to seldom use this facility for pit caring. However, in the larval

rearing tanks, where the eggs were incubated artificially, the wrigglers sought

protection in these structures. The average diameter of the fry pits are reported to be

5.2cm and 4.2cm in deep (Jayaprakas, 1980). Similar to E. suratensis, Ribbink et

al (1981) observed that the nesting pits of T. rendalli, a substrate spawning guarder

is usually not more than 6cm deep and a single nest has been found to have 5-24

pits of varying depths . The wrigglers remain in the pits attached by mucous

threads from three pairs of head glands, where as in mouth brooders these glands are

vestigial or absent (Keenleyside, 1991).

5.3.7.4. Parental care and larval nutrition

Poor fry yield in larval rearing tank when eggs are incubated without the

support of the parent indicate that parents helps in providing the required nutrients

by their bioturbulation activity. Fin digging and micro nipping are two parental

behavior in cichlids which makes food more readily available for the fry

(Quertermus and Ward,1969; Williams,1972; Noakes,1979). During fin digging,

the adults settles on the substrate and with vigorous, rapid beats of the pectoral fins,

stirs up loose materials for feeding the fry. Where as, in ‘micro nipping’ the fry

ingest mucous from the body of the parent and the parent’s epidermal mucous

production is increased during the fry-brooding period, and the young fish

regularly bite at the adult’s body and swallow the mucous (Hildemann,1959).

Both these behavior are regular and common in E. suratensis and E.maculatus even

in the presence of other foods (Ward and Wymann, 1977). Similarly, Seth (2001)

reports that the nest guarding males of giant river catfish, Aorichthys seenghala,

release a white creamy secretion locally known as ‘Chara’ and the young ones are

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nursed and fed over this. Since the major component of parental mucous is

protein, apparently this assist in nutritional management of broods and

larviculture (Khen and Chien, 2006). This would imply that for better fry survival

and fry yield in tank breeding and hatchling care without parental patronage, there

is a dire need to develop alternate sources of nutrition so as to ensure high

hatchling survival.

5.3.8. Larval Development and Fry Nursing

E. suratensis exhibits a prolonged parental care and adults are found with

young ones till they attained size up to 40mm. This would explain the poor growth

rate of E. suratensis in pond culture compared to open water cage culture, where

breeding is totally restricted. However, the parent-offspring association in

E. suratensis is comparatively short as compared to E. maculatus where it has

been reported to be very much extended and last up to 6 months (Ward and Wyman,

1975,1977). Since gonad development is inhibited during parental care, which is

precisely the period when prolactin is supposed to be acting, the spawning interval

is considerably prolonged in such species.

Balon (1975) identified three developmental period within the embryonic

period: the cleavage phase, embryonic phase and the eleutheroembryonic phase.

The process occurs within 12h in Danio rerio, while it takes more than 100 days in

some salmonids. Panikkar (1920) reported that the incubation period of eggs in

E. suratensis vary from 82 to 100 hours. Experiments in relation to amount of yolk

and developmental rates shows that the hatchlings of guarder species retain much

smaller amount of yolk become free swimming in a much earlier state of

development (Noakes, 1991). The embryonic period begins with fertilization of the

egg and ends with the transition from endogenous to exogenous feeding.

The larval period begins with transition to exogenous feeding and terminated

with metamorphosis in to adult organs such as differentiation of the median fin fold

and ossification of the vertebral centra (Noakes and Balon,1982). The larval

development period includes the yolk sac larvae period and the post yolk sac

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larvae period (Liang et al., 2003). In case of E. suratensis, the yolk sac to larval

period commences when the embryo become free of the egg membranes (hatching)

and ends when the yolk of larvae is completely absorbed. The latter stage begins

with complete absorption of yolk occurring on the 6th day and ending with the

emergence of scales. During this period, the body length has been observed to

increase from 4.5 to 6.5 mm on the average and the young ones begin to feed on

attached algae on the substrates. The larvae moves in schools along with the

parents and it reduces the probability of any one individual being preyed by a

predator.

In the present study, seed production has been facilitated in artificial

raceway system by selective stocking of paired brood stock, and by providing

simulated environmental conditions such as transparency of water conducive for

spawning. Feasibility of egg incubation in artificial larval rearing system with and

with out parental patronage was also facilitated. In the context that seed

production of E. suratensis under pond condition has been most unpredictable, and

natural spawning has been dependent almost entirely on a variety of factors the

present study assumes immense significance. The technology of captive breeding

devised and demonstrated with least dependence on finer protocols of hormonal

manipulation is extremely important as it opens up a simpler technology for mass

production of seeds of E. suratensis, a high value species preferred for culture in

fresh and brackish waters.