Indian Journal of Geo-Marine Sciences Vol. 43(4), April 2014, pp. 646-654

Reproductive biology of suratensis (Bloch) from the Vembanad wetland system,

1,2L Bindu* & 2K G Padmakumar

1,2Kerala Agricultural University, Regional Agricultural Research Station, Kumarakom Kerala, - 686 566 1M S M College, Kayamkulam, Alappuzha, Pin – 686 566, Kerala, India *[E-mail: [email protected]]

Received 16 July 2012; revised 15 November 2012

In the present study, data on sex ratio, maturity, Gonadosomatic index, fecundity and oocyte distribution of the pearlspot, Etroplus suratensis, were evaluated. Samples were collected from the landings of Vembanad lake during 2002 - 2004. Male-female ratio was found to be 1:0.8. Maximum GSI in male and female was 1.45 and 4.43 respectively. L50 was 19.5 cm in case of males and 20.0 cm in case of females. Absolute fecundity, varied between 874 and 7554 with an average of 2748. Fish is an asynchronous spawner with different clutches of ova, varied between 0.25 to 2.75 mm.

[Keywords: Etroplus suratensis, Biology, Fecundity, Asynchronous spawner]

Introduction not only for evolving captive breeding protocols but Popularly known as Karimeen, E. suratensis is also for formulating sustainable conservation widely distributed in almost all the brackish and programs. freshwaters of peninsular India. It is essentially a brackish water fish that has become naturally Materials and Methods acclimatized to freshwaters. It is an economically Monthly samples were collected from gill nets and important food fish and is a delicacy that fetch a very scare line fishing during 2002-2004 from the landings high price. Owing to its omnivorous feeding habit, it of Vembanad lake (Lat. 09°31´ & 09°41´N and Long. is much suited to aquaculture (Bindu and 76°21´ & 76°26´E), on the south west coast of India. Padmakumar, 2008). The fish breeds naturally in Total length LT (cm) and total weight WT (g) were confined conditions and is ideally compatible for recorded. Gonads were separated and subsequently polyculture with both freshwater and brackish water weighed to 0.1g and macroscopically analyzed for sex fish and prawn species (Thampy, 1980). determination and maturity stages. In the absence of Information on the biological features of specific sexual dimorphism, sexes were determined E.suratensis is indispensable for devising valid by examining the gonads. A total of 626 fishes, programs for its conservation. Biological comprising 351 males (LT 10-34 cm) and 275 females characterization will also be of immense use for (L 8-30 cm), were examined. Difference in sex ratio identifying the characteristic of the species that T between reproductive and non-reproductive period qualify them as candidates for aquaculture. Critical were compared by applying Pearson χ2 test. On the life history parameters linked to artificial breeding basis of the maturity stages observed, the ovarian and culture, such as sex ratio, size at maturity, gonadosomatic index, fecundity and oocyte cyclicity of E. suratensis could be divided into size-frequency profiles were monitored and biological multiplication, growth, differentiation, maturity and information quantified. Rather than working on a hit depletion phases commonly identified as stage and trial basis, these information were found essential I- immature, stage II- maturing, stage III- mature and ______ripening, stage IV- ripe and ‘stage V- spent’. In *Present address of the corresponding author: females, the maturity stages could be demarcated on BINDU & PADMAKUMAR: REPRODUCTIVE BIOLOGY OF ETROPLUS SURATENSIS 647

the basis of colour and relative size of the gonads with iridescence and pearly white spots. The rayed reference to the body size, ova diameter and the portions of the dorsal and anal fin also become extent of yolk formation, whereas in males, it was slightly reddish. based on the external appearance of the testis. The Male-female ratio in the whole population was size at which 50% of the fishes reach maturity (L50), found to be 1:0.8. A perceptible preponderance of was determined by grouping fishes in stages III and males over females was noticed in the exploited IV separately, into 2.5 cm size groups and their catches. Males, the outnumbered sex, indicated a frequencies were scaled into percentages. In order to higher average size (LT 19.9 cm, WT 211g) than the determine the prime spawning season of the species, females (LT 18.7 cm, WT 170 g). The sex ratio was gonadosomatic index (G.S.I.) was monitored round found to fluctuate widely and in most of the months, the year (n=610) and was estimated by using the males dominated the females (Table 1). In gill netting formula GSI = (weight of the gonad/weight of the ratio was 1:0.5 where as in scare line fishing, it the fish) × 100. was found to be 1:1.1. Chi-square(χ2) analysis indicated significant differences in sex ratio during Preserved ovaries were used to estimate fecundity January and October. (F) and oocyte distribution. Fecundity was estimated Gonadosomatic Index (GSI) in E. suratensis varied by using the formula, F = (No. of oocyte in the between 0 and 1.45 in male and 0.01 and 4.43 in sample/weight of the sample) × weight of the ovary. female. Fluctuations in GSI showed a bimodal For this, a total of 61 ovaries in the stage III and IV pattern, high values during February-April and were collected from fishes ranging between 15.3 and June-October indicating the occurrence of fully ripe 26.7 cm L and 80 to 380 g W . Simple regression T T fishes during these months (Table 2). Apparently, the analysis of the L , W and ovary weight on fecundity T T trend was almost similar for both the sexes. Ovarian were carried out (Bailey, 1995). A small portion of weight shows perceptible and rapid increase during the ovary was taken and the diameters of the April and June and this coincided with the increased intraovarian eggs were measured to the nearest incidence of fully ripe individuals. In males, GSI 0.01mm using an ocular micrometer fitted to a CETI values were however, highest during June, followed trinocular microscope. Oocyte diameter frequency of by February and November. different stages of maturity, pattern of progression of In E.suratensis, all the four stages of maturity were ova during different months and the modes in size represented in varying proportions through out the frequency distribution were also monitored. A total of year and the minimum size of mature specimen was 1940 ova from 86 ovaries were examined. The 14.5 cm invariably, among both males and females. maximum oocyte diameter for mature females was L was 19.5 cm in case of males and 20.0 cm in case obtained by averaging the measurements of at least 50 50 of the largest oocytes (Wu et al., 2001). Table 1—Sex ratio of Etroplus suratensis in collections from Vembanad lake For histological observations, small pieces of ovaries were fixed in Bouin’s solution for 24 h and then Month n Percentage of Ratio χ2 immersed in 80% ethanol. After dehydration with a Male Female Male: series of ethanol and benzene, they were embedded Female in paraffin and were serially sectioned at 3-4 µm January 69 65 35 1:0.5 6.39 thickness and stained with haematoxylin-eosin. February 55 62 38 1:0.6 3.07 March 45 49 51 1:1.0 0.02 Results April 42 43 57 1:1.3 0.86 E.suratensis is monogamous and identification of May 45 56 44 1:0.8 0.56 June 40 50 50 1:1.0 0.00 sexes is possible only during the breeding season. July 49 53 47 1:0.9 0.18 Ovaries were bilobed, left lobe was slightly smaller August 59 53 47 1:0.9 0.15 than the right. Testis was thin and tubular. Genital September 31 52 48 1:0.9 0.03 papillae of the female became reddish and broader October 63 67 33 1:0.5 7.00* and modified into an ovipositor while in male it November 72 58 42 1:0.7 2.00 December 56 54 46 1:0.9 0.29 became thin and pointed. Just prior to spawning, the Total 626 56 44 1:0.8 9.23* males become deeply coloured and the colour bands become strongly marked with a greenish blue n= number of fishes, * Significant (P<0.05)

648 INDIAN J. MAR. SCI., VOL. 43, NO. 4, APRIL 2014

Table 2—Gonadosomatic Index of Etroplus suratensis from Vembanad lake

Male Female Month n = 610 Range Mean + SD Range Mean + SD

January 0.01 - 0.07 0.03 +0.017 0.01 - 2.40 0.76 + 0.628 69 February 0.00 - 1.11 0.06 + 0.187 0.08 - 4.34 0.95 + 1.123 55 March 0.01 - 0.11 0.04 + 0.026 0.21 - 4.38 1.23 + 1.022 41 April 0.01 - 0.08 0.03 + 0.017 0.19 - 4.27 1.35 + 1.274 42 May 0.01 - 0.09 0.03 + 0.020 0.07 - 1.74 0.7 + 0.505 44 June 0.01 - 0.57 0.04 + 0.130 0.20 - 4.41 1.32 + 1.243 33 July 0.02 - 0.18 0.07 + 0.039 0.06 - 3.58 0.97 + 0.885 49 August 0.01 - 0.12 0.05 + 0.041 0.01 - 4.43 1.22 + 1.091 55 September 0.01 - 0.05 0.03 + 0.011 0.05 - 2.96 1.16 + 1.045 31 October 0.01 - 0.70 0.06 + 0.106 0.11 - 3.80 1.08 + 0.904 63 November 0.01 - 1.45 0.06 + 0.221 0.02 - 2.20 0.54 + 0.607 72 December 0.00 - 0.06 0.02 + 0.015 0.04 - 3.98 1.07 + 0.985 56

n = total number of fishes

of females. (Fig. 1). Evidently, size groups up to 12.5 cm were apparently immature or maturing types. Percentage of mature fishes were found to be higher in the size range, 17.6 cm to 35 cm. Mature males and females increased rapidly with size and beyond 27.6 cm, all specimens were found to be of the mature type. Macroscopic appearance of ovary also indicated that both immature and mature ones occurred round the year, and spent ovaries begin to appear from June to August. Apparently, the fish was found to attain maturity by the end of first year. Seasonal changes in the stages of maturity were perceptible in the histological investigations (Fig. 2). The absolute fecundity, varied from 874 (LT 19 cm, WT 180 g) to 7554 (LT 18.8 cm, WT 175 g) with an average of 2748. The fecundity indices in relation to various length groups in E. suratensis is given in Table 3. Relative fecundity or number of eggs produced per gram of body weight, varied from 4 to 51 with an average of 16. Number of eggs per kg body weight ranged between 3655 and 50954 with an average of 13411. The fecundity values were plotted against the respective LT, WT and ovary weight as a scatter diagram (Fig. 3). The diameter of intra ovarian eggs did not indicate any significant difference in size of ova in the anterior, middle or posterior parts of the ovary. Thus, it could be presumed that oocyte size frequency distribution with in the ovary is almost uniform in pearlspots. The size of the ova, however, was found to fluctuate widely between 0.25 to 2.75 mm. The distribution of ova in ovaries of different stages of Fig. 1—Size at first maturity (L50) of E.suratensis collected from maturity in E. suratensis is given in (Fig. 4). Vembanad lake. (a) Male (b)Female, n = number of fishes BINDU & PADMAKUMAR: REPRODUCTIVE BIOLOGY OF ETROPLUS SURATENSIS 649

Fig. 2—Histological appearance of oocyte development in different stages of ovary. Perinucleolus (PE); Yolk vesicle (YS); Primary yolk stage (PYS); Tertiary yolk stage (TYS); and Ripe egg (RE). (Scale bar = 0.1 mm)

In the immature stages, most of the oocytes were Table 3—Fecundity of Etroplus suratensis from the <1.0 mm, and in stage II, the maturing ova from Vembanad lake (Mean values are given) among the immature stocks appear to get separated. Size Group n LT WT Fecundity As the ovary passes from stage II to stage III, size of (cm) (cm) (g) the ova further increased and the second batch of ova got separated from the first. Both the batches of eggs, 15.0 - 17.5 17 16.84 120.29 2300 thus appeared apparently separated. In the ripe and 17.6 - 20.0 24 19.25 182.94 2650 20.1 - 22.5 12 21.49 229.58 3341 gravid fishes, the oocyte size exhibited two distinct 22.6 - 25.0 5 23.82 322.00 4409 peaks at 2.5 mm and 1mm. The large yolked eggs 25.1 - 27.5 3 25.97 370.00 3463 (2.5 to 2.75 mm) comprised almost 49.5% of the total n= number of fishes ova and they appeared separated out from the immature stock (0.75 to 1.75 mm) of eggs constituted of immature eggs in ovaries, in collections 21%. In spent fishes, the mature eggs remained fully made during May-June and October-January was ovulated and all eggs (1.0 to 1.5 mm) that underwent perceptible. It appears that maturation of ova begin in final maturation appeared virtually released. January-February when the ovary is characterized by The pattern of distribution of ova during fully mature ova. A second spawning season with different months is shown in (Fig. 5). Preponderance maturation begins by June and again the modal size of 650 INDIAN J. MAR. SCI., VOL. 43, NO. 4, APRIL 2014

that even within a species and among populations surviving at different geographical locations, there occur major variations in life history patterns. Such variations in reproduction, growth and life history fitness traits are of crucial significance for assessing the long term variability of the fish species (Ponniah and Lal, 2000). Like other such as Oreochromis spp., Etroplus suratensis exhibits some degree of sexual dimorphism, males being larger than females of equivalent age. Variations in morphology of gonad is linked to the breeding habit of the fish (Billiard et al., 1982). Large testis and high GSI values are characteristic to species with sperm competition where as males that invest energy in parental care will have a small testis (Munro et al.,1990; Valdes et al., 2004). The tubular testis in E. suratensis also appear to be linked to their unique habit of parental care and monogamy. It is not possible to sort males and females until a pair is formed and ovipositor of the female becomes enlarged. It has been observed that in males the coloration and iridescence become more intense close to spawning. This peculiar coloration of the fish earned the popular name ‘Green chromide’ to it. Apparently, this coloration enables the male partner to lure the gravid female to the spawning site and the colour patterns are identified to be good communication systems to ensure synchronization of courtship to signal the mate as regards the readiness to spawning activities (Mckaye et al., 1979). Similarly, it appears that the black belly of E.maculatus is a signal that invite its mate for spawning (Keenleyside, 1991).

The significant variation in sex ratio, with Fig. 3—Linear correlation of absolute fecundity with preponderance of males in Vembanad waters is in (a) fish length, (b) fish weight and (c) ovary weight in conformity with the findings of Qasim (1966). E.suratensis. r = correlation coefficient, n = number of females However, Jayaprakash (1980) reported a sex ratio of ova is reached by October. This second spawning 0.84:1.0 for the species in Veli lake and season appears to be staggered and prolonged. Keshava et al. (1988) reported 1:2.73 from the Nethravati – Gurpur estuary of Karnataka, skewed in Discussion favor of females. Similar situation was observed in Assessment of the breeding habits of E. suratensis, Pulicat lake and Mandovi estuary also (Prasadam, in different peninsular waters viz., Pulicat lake, Chilka 1971; Vijayaraghavan et al.,1981). lake, Kali estuary, Nethravathi-Gurpur estuary have One sex in a population is apparently linked to been attempted by several workers (Prasadam, 1971; sexual difference in growth rate; individuals with Jhingran and Natarajan,1969; Raju et al., 1987; faster rate of growth is exposed to low predation and Keshava et al.,1988). However, detailed reproductive loss from population and this influences sex ratio biology with reference to the conservation (Qasim, 1966). Males that grow faster become mature management, has not been attempted. It is well known at a smaller size and at an younger age. It is observed BINDU & PADMAKUMAR: REPRODUCTIVE BIOLOGY OF ETROPLUS SURATENSIS 651

Fig. 4—Frequency distribution of oocyte diameter in different mature stages of E.suratensis. n = number of oocytes measured from each ovary

that the sex which outnumber the other attain a much GSI is a reliable indicator on gonadal maturity; as bigger size. This is apparently true for E. suratensis naturally the weight of the gonad increases with where the males invariably attain a higher size as maturity and when it spawns, there is a reduction in compared to females. Pandian et al., (2001) observed the weight of the gonad on account of the release of that in many oviparous fishes where the duration of gametes (de Vlaming et al., 1982). Studies on the reproductive cycle is short and a single male can GSI in E. suratensis indicate that the fish spawns satisfy several females, the sex ratio is skewed in twice a year and this is also confirmed by gonadal favor of females. This situation however do not hold studies with the occurrence of ripe individual in large good in case of E. suratensis which is characterized numbers during these months. The G S I was by biparental monogamy. The present observations perceptibly low in male E. suratensis as compared support the view that sex ratio falls with growth and to females. females are exposed greater mortality and shorter The breeding season of E. suratensis in Vembanad longevity as compared to males. This problem is lake is indicated to be synchronized with the cessation crucial from the point of view of management of of monsoons and high tidal amplitudes (Thampy, E. suratensis fisheries in Vembanad, where the trend 1980). In Veli lake, the peak breeding season of the is one of rapid decline. fish has been indicated to be October to January and 652 INDIAN J. MAR. SCI., VOL. 43, NO. 4, APRIL 2014

Fig. 5—Monthly changes on the frequency distribution of oocyte diameter. n = number of oocytes measured during each month BINDU & PADMAKUMAR: REPRODUCTIVE BIOLOGY OF ETROPLUS SURATENSIS 653

June to August (Jayaprakas and Nair, 1981). The peak square of its length. Some authors have reported a still breeding season observed in down stream locations in higher rate of fecundity increase and have reported it Vembanad near Poothotta in December with a second to be cube of its length (Bagenal,1957; Varghese, peak in June-July (Krishnan and Diwan, 1990). 1961). Apparently, relation between fecundity and Apparently breeding is influenced by the salinity length is linear. Allen (1951) observed a curvilinear regime in brackish waters. The recrudescence of relationship between fecundity and body weight. In gonads appears to be synchronized by increased food the present study also the relationship between availability, high primary productivity and favorable fecundity and ovary weight has been perceptible, the environmental conditions. Gonadal development has number of ova increased @0.3872 of the ovary been observed to be rapid during post monsoon weight. Apparently, the number of ova produced by months. The high tidal amplitude during this period the fish was closely related to the weight of the gonad appear to provide suitable environmental conditions and the correlation coefficient r was highest in this that trigger breeding. Evidently, in estuarine fishes the case as compared to all other relationships. onset of spawning and recruitment is directly linked Perrone and Zaret (1979) observed that egg size to the tidal rhythm. and fecundity are strongly correlated to parental care Knowledge of the minimum size at maturity is patterns. It appears that, a high degree of parental care useful for regulating mesh size and to avoid is associated with fishes of low fecundity and in fishes recruitment over fishing. The fish has been reported to like Tilapia, which show a high level of parental care, attain maturity at 12.0-12.5 cm (Thampy, 1980; production of gametes is rather low. Moyle and Cech Raju et al., 1987) and 14.0-14.4 cm (Jayaprakas and (2000) mentioned that naturally, the low fecundity in Nair, 1981). In culture ponds, the fish has been mouth brooding cichlids is linked to parents reported to become mature at a fairly small size of ensurance of the survival of the offsprings. 10cm (Vijayaraghavan et al., 1981), as observed in Presence of two distinct group of ova sharply tilapias (Pena-Mendoza et al., 2005). separated from each other confirms that the fish Fecundity of E. suratensis recorded in the spawns more than once a year. As the oocyte present study is higher than earlier observations development and spawning is found to occur at least (Thampy, 1980; Vijayaraghavan et al., 1981; Keshava two times, E. suratensis can be categorized as a et al., 1988). All these observations indicate that multiple spawner that follows a lunar cycle, similar to the reproductive potential of E. suratensis is quite low observations reported by Harahap et al., (2001) in the in comparison to cultivable fishes like major carps. spiny rabbit fish, Siganus spinus, that inhabit the It is however higher than that of other cichlids Okinawan waters. In the context that several clutches like Oreochromis (Fawole and Arawomo, 2000; of oocytes were observed in the ovary and the leading Pena-Mendoza et al., 2005). clutch consisted of oocytes at yolk and maturation stage, E. suratensis can be considered to belong to the The range of fecundity observed in the study was asynchronous category (Wallace and Selman, 1981) found to be higher than that reported for the same and Winemiller (1989) considered them as species in the Veli lake (Jayaprakash et al.,1990). It is ‘equilibrium’ strategists as they show parental care an adaptation to varying environmental conditions and a non seasonal reproduction. that work through the food supply (Wu et al., 2001). Various factors like food productivity, rainfall, Acknowledgement salinity of water and genetic difference of the stock Authors are grateful to Vice Chancellor, Kerala affect fecundity of fishes. Hence fecundity variations Agricultural University for the facilities provided characteristically occur in different populations and during the study period. even in same population in the same water body during different years. References In the present study also, regression between 1 Allen K R, The Horokiwi stream: A study of trout fecundity and L , W and ovary weight indicated a population, Fish Bull N Z Wellington, 10 (1951) 1-238. T T 2 Bagenal T B, Annual variation in fish fecundity, J Mar Biol direct proportional increase and the values were Ass U K, 36 (1957) 377-382. significant in case of ovary weight and fecundity. In 3 Bailey N T J, Statistical methods in Biology, The English general, the fecundity of a fish increases with the University Press, London, (1995) 255 p. 654 INDIAN J. MAR. SCI., VOL. 43, NO. 4, APRIL 2014

4 Billiard R, A Fostier, C Weil & Breton B, Endocrine control 19 Pandian T J, Koteeswaran R & Kirankumar S, Breeding of spermatogenesis in teleost fish, Can J Fish Aquat Sci, strategies and techniques for ornamental fishes, Paper 39 (1982) 65-79. presented in NBFGR-NATP Workshop, Captive Breeding of 5 Bindu L & Padmakumar K G, Food of the Pearlspot, Prioritised Cultivable and Ornamental Fishes for Commercial Etroplus suratensis (Bloch) from the Vembanad lake, Kerala, Utilization and Conservation. 29-30 July, National Bureau of J Mar Biol Assoc India, 50 (2008) 156-160. Fish Genetic Resources, Lucknow. U.P., India (2001) 12 p. 6 de Vlaming V L, Grossman G & Chapman F, On the use of 20 Pena-Mendoza B, Gomez-Marquez J L, Salgado-Ugarte I H the gonadosomatic index, Comp Biochem Physiol, 73A & Ramirez-Noguera D, Reproductive biology of (1982) 31-39. Oreochromis niloticus (Perciformes: Cichlidae) at Emiliano 7 Fawole O O & Arawomo G A O, Fecundity of Sarotherodon Zapata dam, Morelos, Mexico, Rev Biol Trop., 53 (2005) galilaeus (Pisces:Cichlidae) in the Opa reservoir, Ile-Ife, 515-522. Nigeria, Rev boil trop, 48 (2000) 201-204. 21 Perrone P Jr. & Zaret T M, Parental care patterns of fishes, 8 Harahap A P, Takemura A, Nakamura S, MD. S Rahman & Amer Nat, 113 (1979) 351-361. Takano K, Histological evidence of lunar-synchronized 22 Ponnaih A G & Lal K K, Utility of life history parameters in ovarian development and spawning in the spiny rabbitfish conservation and genetic up gradation programmes, in: Siganus spinus (Linnaeus) around the Ryukyus, Fish Sci, Endemic Fish Diversity of Western Ghats, edited by 67 (2001) 888-893. A G Ponniah and A Gopalakrishnan (NBFGR-NATP 9 Jayaprakas V, Biology of Etroplus suratensis (Bloch), Ph.D. Publication-1), National Bureau of Fish Genetic Resources, thesis, University of Kerala, Thiruvananthapuram, (1980) Lucknow, U P, India. (2000) pp. 286-288. 434 pp. 23 Prasadam R D, Observations on the biology of the Pearlspot, 10 Jayaprakas V & Nair N B, Maturation and spawning in Etroplus suratensis (Bloch) from the Pulicat Lake, Madras, Pearlspot, Etroplus suratensis (Bloch), Proc Natl Inst Sci J Inland Fish Soc India., 3 (1971) 72-78. India, B47 (1981) 828-836. 24 Qasim S Z, Sex ratio in fish population as a function 11 Jayaprakas V, Nair N B & Padmanabhan K G, Sex ratio, of sexual difference in growth rate, Curr Sci, 35 (1966) fecundity and Length weight relationship of the Indian 140-142. Pearlspot, Etroplus suratensis (Bloch), J Aqua Trop, 25 Raju M B, Kusuma M S & Neelakantan B, On some aspects 5 (1990) 141-148. of the maturation and spawning of the pearlspot, Etroplus 12 Jhingran V G & Natarajan A V, A study of the fisheries and suratensis from the kali estuary, Karwar, Matsya, fish populations of the Chilka lake during the period 12-13 (1987) 34-38. 1957-65, J Inland Fish Soc India., 1 (1969) 49-126. 26 Thampy D M, Culture of Etroplus suratensis (Bloch) in 13 Keenleyside M H A, Fishes Behaviour, Ecology and Summer Institute of Brackishwater Capture and Culture Evolution, Chapman and Hall, New York, (1991) 378 pp. Fisheries. CIFRI, Barrakpore (1980). 14 Keshava, Joseph P S & Joseph M M, Reproduction of the 27 Valdes P, Alcazar A G, Abdel I, Arizcun M, Suarez C & pearlspot Etroplus suratensis (Bloch) in the Nethravati- Abellum E, Seasonal changes on gonadosomatic index and Gurpur estuary, Mangalore. in: Proc First Indian Fisheries maturation stages in common Pandora, Pagellus erythrinus Forum, edited by M Mohan Joseph, Asian Fisheries Society, (L.). Aquacult Int, 12 (2004): 333-343. Indian Branch, Mangalore. (1988) 237-241. 28 Varghese T J, Observations on the biology of Reconda 15 Krishnan L & Diwan A D, Seasonal changes in gonads and russelliana (Gray), Indian J Fish, 8 (1961) 96-106. their relationship with gonadotrophs of the pituitary in 29 Vijayaraghavan, Krishnakumari L, Gopinath V J & Etroplus suratensis (Bloch), J Mar Biol Ass India., Dhawan R M, Aquaculture of pearlspot Etroplus suratensis 32 (1990) 5-9. in an estuarine pond: Environmental characteristics, primary 16 McKaye K R, Weiland D J & Lim T M, Comments on the production, growth and cost benefit ratio, Indian J Mar Sci, breeding biology of Gobiomorus dormitor (Osteichthyes: 10 (1981) 82-89. Eleotridae) and the advantage of schooling behaviour to its 30 Wallace R A & Selman K, Cellular and dynamic aspects of fry, Copeia, 3 (1979) 542-544. oocyte growth in teleosts, Am Zool, 21 (1981) 325-343. 17 Moyle B P & Cech Jr. J J, Fishes an Introduction to 31 Winemiller KO, Patterns of variation in life history among Ichthyology. Prentice Hall. New Jersey, USA (2000) South American fishes in seasonal environments, Oecologia, 123-144. 81 (1989) 225-241. 18 Munro A D, Scott A P & Lam T J, Reproductive Seasonality 32 Wu C C, Su W C & Kawasaki T, Reproductive biology of in Teleosts: Environmental Influences, CRC Press Inc., Boca the dolphin fish Corphaena hippurus on the east coast of Raton, Florida. (1990) 109-124. Taiwan, Fish Sci, 67 (2001) 784-793.