Fishery and diet composition of the cobia Rachycentron canadum (Linnaeus, 1766) exploited along Karnataka coast

Abstract

The fishery and food of cobia, Rachycentron canadum caught off Karnataka, south-west coast of India was studied during 2007-2010. An estimated 302 t was landed annually along this coast which formed 0.1% of the total fish catch of the region. Peak landings were recorded during October followed by April. Gillnets landed large sized cobia and contributed to the bulk of the catch (53%). Maximum catch by this gear was during September-October. Next dominant gear was trawl which landed fishes of all size groups with maximum catch during April-May. Trawl landings contributed 45% of the total cobia landings. The fishery was comprised of fishes of length range 26 - 125 cm TL with the mean at 58 cm. Juveniles dominated the catch. Contents of 177 non-empty stomachs were analysed for the index of relative importance (IRI) and prey specific abundance (PSA). R. canadum was found to be nonselective generalist carnivore feeder, foraging on micronektonic pelagic or benthic organisms (crustaceans, fish and molluscs) available in the epipelagic waters. Teleost fish (55%), crustaceans (35%) and molluscs (10%) contributed to the diet. Decapterus russelli (18.0%) and Encrasicholina devisi (10.0%) were the dominant finfish groups; Acetes sp. (21.1%) followed by crabs (Charybdis spp. and Portunus spp.) with an IRI of 12.9% were dominant among crustaceans and squids (Loligo spp.) (5.8%) and octopus (4.1%) comprised the dominant molluscans prey items.