Food spectrum dynamics of anadromous Hilsa, Tenualosa ilisha (Hamilton, 1822) inhabiting River Brahmaputra, India curtailing apprehension of food selectivity: An insight into its domestication

Abstract

Food and feeding habits of Tenualosa ilisha collected from two sampling locations in Brahmaputra River, Assam, India for a period of 12 months from May 2018 to April 2019 were studied. Index of preponderance revealed semi-digested animal matter (25.92 %) as the most dominant food item followed by Bacillariophyta (23.32 %). 31 genera of phytoplankton and 15 genera of zooplankton were observed in the gut of the species. Major groups of zooplankton include cladocerans, copepods, followed by rotifers, while diatoms, green algae and blue green algae were dominant phytoplankton groups. The anadromous tropical shad is planktivorous by nature and has a preference for zooplankton in smaller size groups (< 250 mm) and phytoplankton in larger size groups (> 250 mm). GaSI values (mean±SE) ranged from 1.50±0.14 to 6.93±0.89 and HSI values from 0.58±0.06 to 1.54±0.15. Index of fullness was found to range from 7.08±0.42 to 1.81±0.40. Feeding intensity, GaSI, HSI values showed seasonal variation, found to be low during October to December and high during February to June. Size group-wise analysis of feeding intensity showed high feeding intensity in lower size groups
(< 250 mm) and comparatively low feeding intensity and high percentage of empty stomachs in higher size groups (> 250 mm). RLG values ranged from 1.181±0.028 to 1.450±0.052. Monthly average RLG values were found to be highest during November and in the size group of 351 – 400 mm. Changes in food composition were noticed in both months and as well as size groups.