Study on preferred food items of hilsa (Tenualosa ilisha).

Abstract

The Indian shad hilsa (Tenualosailisha) is one of the most important tropical fish of the Indo-Pacific region. There is a compelling need for domestication and culture of the species for conservation and rehabilitation of its declining fishery and information on the food and feeding habits of the species is essential for its domestication. For this purpose a study on gut content analysis of T. ilisha of different size groups were carried out to know the preferred food items of the species in Hooghly estuarine stretch in West Bengal. Fish specimens of different size groups were collected from different habitats viz., marine (Namkhana and Fresser Gunge), brackishwater (Kakdwip Lot.8 and Nischintapur) and freshwater (Godakhali, Sultanpur and Diamond Harbour) habitat in West Bengal. The specimens were dissected and gut contents were analyzed by frequency of occurrence of food items and volumetric analysis method. Fishes (n=90) were divided into 9 different size groups as per their body weight i.e. 1-5 g, 5-10 g, 10-30 g, 30-50 g, 50-100 g, 100-200 g, 200-400 g, 400-600 g and 600-800 g. Frequency of occurrence of gut contents (%) of fishes below 10 g size indicated that diatoms were the major items in the gut with Coscinodiscussp. andBiddulphiasp. asdominant among diatoms. In 10- 30 g size group, copepods, diatoms and filamentous algae were the major items in the gut and Coscinodiscussp. was dominant among diatoms. In 30-50 and 50-100 g size group, diatoms followed by copepods formed the major food items. Coscinodiscussp. and Nitzschiasp. were dominant in 30-50 g group whereas Biddulphiasp. and Pleurosigmasp. were dominant in 50-100 g group. In fishes of above 100g diatoms formed the major food items followed by copepods. Among the diatoms, Coscinodiscussp. And Biddulphiasp. Debasis De et al

648 were dominant in 100-200 g and 200-400 g group. Coscinodiscussp., Nitzschiasp. and Asterionellasp. were dominant in 400-600 g group whereas Coscinodiscussp. andThalassiothrixsp. were dominant in 600- 800 g group. Majority of items in the gut were in digested state. Sand particles (4.17 to 37.50% of total gut volume) observed in the guts of majority of the specimens, may be attributed to turbid habitat from where animals were caught. Volumetric index analysis (%) of gut samples indicated that digested food occupied highest volume in 1-5 g size groups.Copepod occupied more volume than diatom in fishes of 5 to 50 g body weight range,whereasdiatoms occupied maximum volume in fishes weighing more than 50g. The study indicated that hilsa (Tenualosailisha) prefer copepod in their early stages and shift their preference towards diatom when they grew beyond 50 g size.