Diet composition and feeding dynamics of Trichiurus lepturus Linnaeus, 1758 off Gujarat, north-west coast of India
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The largehead ribbonfish, Trichiurus lepturus Linnaeus, 1758 forms a major fishery along north-west coast of India comprising the two coastal states of Gujarat and Maharashtra. Diet composition was analysed for five years (2010-2014) to understand shifts if any in the prey items. Seasonal changes in the prey items were studied for three years (2012-2014) to explore the temporal dynamics of prey availability in the ecosystem and in largehead ribbonfish guts. Feeding indices viz., Stomach fullness index (SFI), empty stomach ratio (ESR), gastrosomatic index (GaSI) and relative gut length (RLG) explained the feeding behaviour, seasonal dynamics and ontogenetic shifts in prey items. The Vacuity Index (VI) was estimated as 37.56%, indicating that T. lepturus is a carnivore and relatively edacious. Diet of T. lepturus comprised of fishes (47.16%), crustaceans (45.22%), molluscs (4.33%) and miscellaneous items (3.28%). Acetes sp. was the most dominant prey item during the study period. Feeding intensity was found to be high during the post-monsoon months which coincided with the period of gonadal maturation of the fish. Significant variations (p<0.05) were seen in the feeding indices during different months, different sizes and between sexes due to the availability of prey items, physiological changes and ontogenetic shifts. A detailed knowledge on diet composition, temporal dynamics in diet patterns and feeding indices can reveal the trophic interaction of prey-predator, resource abundance and fluctuations which are important inputs in
ecology-based fishery management models/tools.