Variations in growth rates of cage cultured Asian seabass Lates calcarifer (Bloch, 1790) and cobia Rachycentron canadum (Linnaeus, 1766) in relation to environmental quality of marine farm at Karwar, India

Abstract

Growth rates of cage cultured Asian seabass Lates calcarifer (Bloch, 1790) and cobia Rachycentron canadum (Linnaeus, 1766) in relation to the water and sediment quality of marine farm at Karwar for two consecutive crops (2012-13 and 2013-14) were analysed. No significant variation was observed in the specific growth rate (SGR) of both the species between the crops. But within a crop, variations were observed in the SGR and absolute growth rate (AGR) of both the species (p<0.05). Specific growth rate of cobia was 0.75 and 0.78 % day-1 in 210 days of culture for the years 2012-13 and 2013-14 respectively. Physico-chemical parameters of water at cage and reference sites did not vary significantly, except for ammonia-nitrogen and nitrate-nitrogen levels at cage site between and within the crops. No significant variation was observed in total bacterial and Vibrio loads of water in cage site between the crops but significant variation was observed within the crop. The results revealed that temperature (r = +0.61 for 2012-13 and +0.63 for 2013-14) and salinity (r = +0.6 for 2012-13 and +0.5 for 2013-14) played a major role on SGR of cobia during both the crops with higher AGR recorded during summer months. In case of Asian seabass, no significant impact of temperature and salinity on SGR was noticed during the experimental period.