Indian sand whiting, Sillago sihama (Forskal) forms a dominant

species in the estuarine fish catches during the south-west monsoon when

they are in great demand and fetch a high price as sea fishing remains

suspended due to rough weather conditions.

The paper deals with preliminary observations on certain aspects

of the biology of the fish related to its culture. The ability of the

species to withstand very wide raoges of salinity makes it suitable for

culture io both brackish and fresh waters

Devaraj, K V

James, P S B R

Varghese, T J

CMFRI Digital Repository

Possibilities of culture of Si/laco sihama in brackish waters 213 Observations Maturation The maturation process was mainly studied by tracing the development of ova to maturity by ova-diameter studies and monthwise distribution of matnrity stages according to size groups. Development of ova to maturity The size distribution of ova in various stages of maturity is shown in Fig. I. The size of the ova varied from 2 oc.m.d. in stage I to 47 oc.m.d. in stage V (1 oc.m.d.~0.016 mm). Except in stages [ and If, ova smaller than 5 oc.m.d. were not measured as these were the transparent, immature ova present in all the ovaries. The ova in stage I range in size from 1 to 6 oc.m.d., a great majority of them being in the size group 1 io 3 o_c.m.d. The size of ova in stage If varies from 1 to 12 oc.m.d. The polygon for this stage indicates the with-drawal of a batch of ova with a modal size of 5 oc.m.d. to undergo maturation. In stage III, the maturing group of ova is well demarcated from the immature stock by the mode at 20 oc.m.d., the largest ova measuring 24 oc.m.d. In the same stage, a smaller group of ova with a mode at 8 oc.m.d. indicates the withd rawal of yet another batch for maturation. In stage IV, the mode of the advanced group shifts to 23 oc.m.d., the maximum size ' of ova in this stage being 300c.m.d. The second group of maturing ova indicated in stage III is, however, not distinct. In stage V, the maximum size of ova is 48 Dc.m.d, and the mode of the advanced group shifts from 23 oc.m.d. (in stage IV) to 38 oc.m.d. These, obviously are the OV~ which would be shed in the ensuing spawning season. In this stage, a second maturing group of ova is seen with a mode at 23 oc.m.d., which evidently corresponds t? the mode at 8 oc.m.d in stage III but not seen in stage IV. This second group of ova, with a distiuct mode at 23 oc.m.d. in 'tage V, are not likely to be released along with the most advanced group, but develop further after the first batch is shed. This view is further substantiated by the fact that a similar size group having a mode at 20 oc.m.d. is present in the ova diameter frequency polygon of the spent ovaries (stage VII). In the absence of actual record of females in spawning condition (stage VI), the presence of a mature and a separate maturing group of ova which has undergone half the maturation process in the ovary of stage V, indicates that the same individual fish breeds more than once in a year and that at least two batches of ova are shed with some interval in between. Size at first maturity For this study the fish were grouped according to a size interval of one centimeter and the corresponding maturity slages tabulated separately for females and males. The data indicate, females were in stage I from 121 to 240 mm ; stage Il from 161 to 290 mm; stage III from 161 to 330 mm ; stage IV from 221 to 320 mm ; stage V from 191 to 310 mm ; stage VII from 21 I to 290 mm in total length. Females in stage VI were not available for study. The smallest spent female fish recorded was 21 I mm. Males were in stage I from I I I to 290 mm ; stage Il from 141 to 280 mm; stage III from I~I to 240 mm ; stage IV from 161 to 260 mm ; stage V from III to 250 mm ; stage VI 214 3D 2.0 1.0 3D 2.0 1.0 5.0 >- 4.0 ~ 3.0 I&J ~ 2.0 d I&J 1.0 a: ..... I&J ~ 3.0 ~ 2.0 I&J u 1.0 a: ILl a.. 4.0 3.0 2.0 1.0 8.0 6.0 4.0 2.0 1.0 P. s. B. R. JAMBS AND OTHBRS· STAGE -VII STAGE-V STAGE-IV STAGE-Ill STAGE-II STAGE-I 25811 14172.0232629323538414447 .oCULA R MICR.oMETE R DIVISI.oNS Fig. 1.-O\'a d-iameter frequency polygons of ovaries of S. siluuna in different stages of maturity .. Possibilities of culture of Sil/ago sihama in bracki sh waters 215 from 151 to 260 mm in total length. No males in stage VII were recorded . The smallest male on record in spawning condition was 151 mm in total length. The above observations also indicate thai' .rte males mature at a much smaller size than the femal es. Spawning Examination of the ova diameter frequencies of mature ovaries of S. sihama indicates that they contain three distinct groups of ova, namely, immature, maturing and mature. As the fish approacbes the spawning season, the most advanced group of ova gets separated from the following maturing group wbich has undergone about half the maturation process. Afrer the elimination , of tbe first group (mature) the second group (maturing) obviously takes the place of tbe first group, by which time a second maturing group is expected to appear. I If tbe spawning period of the species is restricted, all the fish collected at any parti-cular time are expected to belong to more or less the same stage of maturity. In the present case, a sample collected on a particular day contained fi sh in at least tbree different stages of maturity and in many months, advanced stages of maturity coupled with partially spent and spent stages were recorded indicating the absence of a restrhited spawning period. A total of 204 femal es and 343 males were examined for the determination of the spawning season. The month-wise distribution of the maturity stages of female S. sihama is shown in Fig. 2. Stage V occurs from A ugust to Ocrober and January to March and in some of these months spent fish (stage VII) also occur. There were no data for November and December, but it is expected that advanced stages (stages V and VI) would be found in these months also. The distribution of the maturity stages in male is shown in Fig. 3. The data indicate that stages V and VI were available from July to September and January to April. Data were not available for November and December, but as in the case of female, the two advanced stages could be expected in these months also. From the above observations, it appears tbat the spawning period of S. sihama is a prolonged one, extending over several months from August to April. Occurrence of juve-niles in a number of months supports the above inference. The data also suggest that an individual fish releases the egg! in batches at different times , thereby indicating a prolonged breeding period. Fecundity Since the species spawns over a long period, with individual fish shedding the oVa in batches, it is difficult to estimate the total number of ova that would be released by each 216 P. S. B. R. JAMES AND OTHERS fish. TherefDre, counts .of the number of ova in the large.t group present in the ovary at the time' .of capture .of the fish were made to indicate the reproductive potential. The number of oVa thus enumerated was observed to range from I I ,304 to 1,00,593 in indivi-duals measuring 207 t.o 317 mm in tDtallength. 80 SEP't. MAR. .- JUL. . 60 40 r-r-r-20 0 Innn In In ~ n In ~ 80 AUG. FEB. JUN. .. 60 .., z "' ~ 40 - -~ => .., g 20 "' C> ~ 0 "nn r-n n n n ~ 60 u ~ "' JUL. JAN. ~ MAY, r- r- 1972 ~ 40 -r- r-20 0 n In n 1,-, 60 r-JUN. OCT. r- APR. 1971 60 40 20 0 nn nnnn n Inn Il HI IV V VI VU II III IV V VI VII II II.l IV V vt VII MATURITY STAGES Fig. 2. - Mooth-wise percentage occurrence of maturity stages in females of S. sihama. Observations on seed resource5 Attempt. t.o c.ollect the naturally occurring seed .of S. sihama from the Nethravatlty and Gangolly estuaries were made .once in a m.onth fr.om January to Jury, 1972. The observati.ons indicate that the y.oung .ones .of this fish are available in good numbef5 in the Gangolly estuary. During the ab.ove period, .only a few young .ones c.ould Possibilities of culture of Siliago sihallla in brackish waters 217 ·be collected fr om the Netbravathy estuary, indicating the paucil y of the same. Thorefore, only the particulars of collection from Gangolly estuary are given in Table I. Juveniles of this species are abundant in January and· February as compared to other months upto July. There were no observations for the period August (0 December. Young ones could be effectively collected at low tide than at high tide. T he areas of collection are close to the mouths of the rivers, extending about 3 km upstream. Young ones were observed to con-gregate in shallow wat er (about a metre in depth) around exposed sandy areas at low tide. Scaring the fish with the help of scare lines and production of sound into the bag of the net appear. to be tbe best method of collection . After colleclion, if young ones were kept crowded in containers even with cbange of water, it led to heavy mortality. In the present study, transportation of 30 fisb in 6 litres of water contained in an oxygen fill ed plastic bag over a distance of 100 km was found successful wi thout any mortality. SEPT . MAR. JUt. • 0 20 O~~~~ ____ ~iL~~U-~~-L ______ ~-L~ __ ~ __ ~-L--4 80 60 80 60 40 20 AUG . JUN. 1971 FEB. JUN. OCT. APR. OLL~-L __________ ~~U-L-__________ -U-L~L-U-LL~ __ ~ II III IV V VI VII II III IV V VI VII MATURITY STAGES II III IV V VI VII I Fig. 3.-Montb-wLse percentage occurrence of maturity stages in males of S . silzama. 218 P. S. B. R. JAMES AND OTHERS TABLE I Particulars of collect ion of juveniles of S. sifmma from the Gangolly estuar}' Duration of No. of fish Size range Salinity Date collection (minutes) collected (mm T.L.) (%01 11.1.72 60 100 61-151 4.2.72 90 323 40- 93 29.02 22.4.72 60 28 45- 86 24.74 25.5.72 120 26 85-114 29.16 19.6.72 6() 10 34-115 20.29 29.7.72 90 29 75-172 3.85 Acclimation Juveniles and young ones of the fish collected from the estuaries were acclimated from brackishwater to freshwater under varying conditions. Direct transfer of fish from brackish\vater to freshwater led to mortality. Transfer from brackishwater to water which was made up of 50% brackishwater and 50% freshwater was also found to affect the fish . Gradual transfer from brackishwater to freshwater by stages spread over at least a week appeared to be the best method of acclimation. The observed values of percentage survival through acclimation were 30 ( 7 days); 55 ( 23 days) and 60 ( 24 days) in experiments conducted in aquaria in a water temperature range of 24.5 to 33.5°C. The atmospheric t emperature during the period varied from 26.0 to 3J.O°C. Though the fish could be acclimated to freshwater. its survival in the same needs further study. The maximum period of survival in fresh water during the present study was about 70 days. During the course of the experiments on acclimation, a variety of artificial feed was offered to fish of all sizes . They included chopped fi sh meat, prawn pulp, fresh water worms, maggots, earth worms, small freshwater snails, blood clots. freshwater plankton and pelleted feed . The fish did not show any attraction to these foods. Smaller fish (upto 100 mm in total length), however, accepted prawn pulp which larger fish refused. The larger fish readily accepted polychaetes. Fish in advanced stages of maturity do not appear to feed. These observations indicate certain selectivity in feeding, which also seems to vary with age. Discussion The only earlier study whieh includes some o f the aspects of the biology of S. silzama reported in this paper was that of Radhakrishnan (1957). The samples for his study were obtain.cd from the Palk Bay and Gulf of Mannar if' the region a round Mandapam , thn s based on fish avai lable at sea unlik e the estuarine fish samples investigated here. It is noteworthy in this connection that while this species contributes to commercial catches from the sea in the Palk Bay and Gulf of Mannar , in the South Kanara region it contributes to Possibilities of culture of Sil/ago sihama iu brackish waters 219 commercial catches from the estuaries. In tbe sea off this coast, tbe species is caught only as stray specimens whicb are usually not more than 120 mm in total length whereas in the estuaries fish upto a size of 323 mm are caught. Krishnamurthy (1969) also reported the occurrence of larger fish in the Pulicat Lake. According to Radhakrishnan (1957), tbe ripe ova range in size from 0.417 to 0.517 mm but in the present study, the mode of this group of ova was found to be at 0.608 mm witb a maximum size of 0.768 mm, while the mode for mature eggs reported by him corresponds witb that stated in tbe present study. Since a good difference in size has been found between the modal sizes of mature and ripe groups of ova in stage V, individual fish appears to spawn more than once in a year. The conclusion however, in both tbe studies, points to a prolonged spa\'·ming season for the species. Spawning season according to Radbakrishnan (1957) extends from about August to February with peak in October. In thc present study also it was found to extend from August to April. Chaudhuri (1923) as quoted by Radhakrishnan (1957) suggested that spawning of ' S. sihama takes place in the mouths ofrivers and that the fish, a permanent inhabitant of Chilka Lake, goes out to the sea or the mouth of the lake for breeding. The present study which includes large fish from the estuary in advanced stages of maturity and ~pawning condition supports th e above view, specially since the samples fr om the sea do not include any mature or large fish as also stated by Radhakrishnan (1957) in his study. The food of S. sihama from Pulicat Lake was studied by Krishnamurthy (1969). He concluded that there are three trophic phases in the life of this fish. The fry feed mainly on copepods and the adults on polychaetes. The fingerlings have a mixed diet of polychaetes, copepods and other crustaceans. In the stomach contents of fish from sea, there was predominance of prawns and other crustaceans while polychaetes occupied an insignificant place in the food of the fish from this environment. In the experiments on artificial feeding during acclimation from brackishwater to freshwater, it wa5 found that fingerlings accepted prawn pu lp and polychaetes readily, while adults fed only on polychaetes which is in agreement with the observations of Krishnamurthy (1969). Fishermen report that the fish in the spawning condition do not take bait on hook. The size at first matur ity has been stated to be 130 m by Radhakrishnan (1957). In the present study, however, ma1 es were found to mature at 151 ill and females at 191 m. This di ffe rence could be explained as due to difference in the nature of material in the two cases . The present study therefore confirms earlier observations made on the spedes in other regions regarding its ma1urity. spawn ing and food habits and indicates the possihilify of hypophysat ioll of the species because of the availability of mature and running fish in the estuaries ill the region . Preliminary attempts at hypoph)'sation indicated that while chances 220 P. S. B. R. JAMES AND OTHBRS to obtain males in proper condition are mort, chances for obtaining females simultaneously are limited. This neces<itates building up a stock of brood fish for the purpose of hypoph ysa tion. References KrishDamurtby. K. N., 1969. Observations on the food of the sandwhiting Sillogo sihama (Forsk;l) from Pulicat Lake. J, Mar. bioi. Ass. India, I J (1 & 2) : 295-303. Radhakrisbnan. N., 1957. A contribution to the biology of Indian sand whiting, Sillogo sihama (FOrsk~I). Indian J. Fish . 4 (2) : 255-83. -:0:-

Some observations on the possibilities of culture of the Indian sand whiting Sillago sihama (Forskal) in brackish waters

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Some observations on the possibilities of culture of the Indian sand whiting Sillago sihama (Forskal) in brackish waters

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