(Received : 18.05.2012; Accepted : 03.11.2012 ...

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Nabadwip, Kalna, Balagarh, Tribeni, Hooghly ghat,. Nawabganj, Baranagar Godakhali, Raichawk,. Diamond Harbour, Harwoodpoint, Nischintapur and.
J. Inland Fish. Soc. India, 44(2): 42-48, 2012 REPRODUCTIVE BIOLOGY OF INDIAN SHAD (TENUALOSA ILISHA) IN THE BHAGIRATHI-HOOGHLY STRETCH OF THE GANGA RIVER SYSTEM Utpal Bhaumik, Sritama Bose, B.B.Satpathy, R.K.Manna, A.K.Sahoo and C.M.Roshith Central Inland Fisheries Research Institute, Barrackpore, Kolkata 700120.

(Received : 18.05.2012; Accepted : 03.11.2012) Hilsa (Tenualosa ilisha ) is the major fishery component in the Bhagirathi-Hooghly river system accounting for about 15-20% of total fish landings. It is an anadromous fish, which migrates into the Bhagirathi-Hooghly river system from the Bay of Bengal for breeding and spending their earlier part of life. Aspects like gonado-somatic index, fecundity, maturity and breeding season were studied during 2011 and 2012. The gonado somatic relation for male could not be drown due to highly fluctuating values and for female it was y=8.837+0.004x. Fecundity ranged from 44,002 to 15,54,894 in the size range of 208 mm to 475 mm and 105 g to 1175.5 g. The minimum fecundity value recorded was lowest ever recorded for the species. The first maturity size for males tallied with the previous record but the same was comparatively lower for the females. Breeding season varied with year and indicated linkage with the monsoon and intensity of flood.

Keywords: Tenualosa ilisha, Gonado somatic index, Fecundity, Maturity, Ganga.

Introduction Hilsa, the Indian shad Tenualosa ilisha (Hamilton) belongs to the sub-family Alosinae of family Clupeidae. The fish is major component in the Bhagirathi-Hooghly river system accounting for about 15-20% of total fish landings. Hilsa, the prime anadromous species of the Bay of Bengal region migrates to fresh water river habitats in Bangladesh, Mayanmar, India for breeding and spent early part of its life. In India, BhagirathiHooghly river system stands one of the important destinations for the species. Because of its behavioral, biological and commercial importance, the species had been a subject of extensive research since last centuries. Investigation of various aspects of biology, migration and fisheries had been carried out in different river system of the country by different workers time to time. It is evident from their findings that the species differed in various

biological aspects from one system to the other, which might be due to eco-environment variabilities. Likewise breeding season, spawning peaks and periods, age at the first maturity, fecundity and somatic growth pattern had also been studied and reported to vary in the Hooghly estuary by different workers. Hydro-ecological conditions of the Hooghly estuary have undergone conspicuous changes due to Ganga water diversion and subsequent adaptation of management measures through the Farakka barrage since mid seventies. Time scale data available in this regards (Sinha et al., 1996) revealed remarkable changes in salinity distribution pattern of the estuary, and also though not pronounced, in other hydrological characteristics. Biologically the fresh water flora and fauna also gradually got dominance replacing many of the brackishwater and marine forms. Since, these hydro-biological alternation are 42

existing over prolonged period these have turned to be phenomenal for the estuary. The present attempt was to investigate the influence and impact of changed eco environmental conditions of Materials and methods Entire stretch (523.59) of HooghlyBhagirathi river from sea face onwards upto the feeder canal lock gate at Farakka was studied at fifteen sampling station viz., Farakka, Lalbagh, Nabadwip, Kalna, Balagarh, Tribeni, Hooghly ghat, Nawabganj, Baranagar Godakhali, Raichawk, Diamond Harbour, Harwoodpoint, Nischintapur and Freserganj in decending order (Fig. 1). Hilsa specimens were procured from all these stations round the year depending on availability. For better coverage and obtaining every size group of the fish, samples from landing stations and from fishing nets were collected. Thus, adult hilsa from the gill nets and juveniles caught through the bag nets were equally represented in the samples. Fortnightly sampling with coverage of full moon and new moon phases were followed.

Fig.1. Hooghly-Bhagirathi river system and sampling sites

Fish samples were immediately preserved at the field itself in ice box (if those were adults and bigger size) or in 5% formaldehyde for

reproductive biology of hilsa in Hooghly – Bhagirathi River.

comparatively smaller fishes. For first hand sorting, the mature males were segregated at the sites by testing presence of milt on application of slight pressure on abdomen. Females comparatively bigger in size, could be identified from the shape of the abdomen and vent condition. The remaining fishes were dissected, examined and segregated in maturing males and females and immature ones without sex differentiation were discarded. Fishes above 100 mm size were considered for studying reproductive biology. Month wise as well as location specific data on various aspects of reproductive biology were recorded during in period of two years 2010-11 and 2011-12. Results and Discussion Fecundity Fecundity is one of the important aspects of reproductive biology of fish species, which provides information on the number of eggs in the ovary prior to the next spawning season. Altogether 212 females’ samples collected from the entire stretch were examined for determining fecundity of the individual. The ovaries with mostly mature eggs were considered for fecundity determination. Weight of demoisturised ovary for individual fish was recorded. A known amount (10% of total ovary weight) of egg samples from upper, middle and lower portion of both the ovaries were collected in equal portion and mixed up thoroughly. Representative (in weight) sample of the total eggs was then taken out and counted with naked eye for numerical abundance. Finally the total no of ova was calculated with necessary multiplications for fecundity estimation of the fish. In the present study fecundity of the samples was worked out and the number of ova ranged between 44,002 and 15, 54, 894 for the fishes in the size range of 208 to 475 mm in length and 105 to 1175.5 gm in weight. The fecundity values were finally plotted against total length and total weight (fig.2 and fig.3). A straight-line relationship of 43

fecundity was evident with length and also weight of the fish. The regression equation calculated by adopting least square method between total length and fecundity was log F=2.262+2.260 log L and that for total weight and fecundity was log F=3.153+0.968 log W. Respective correlation coefficient (r) values for total weight and fecundity

were 0.5486 (P