Effect of different stocking densities on pre-slaughter stress based on respiratory parameters in Nile tilapia (Oreochromis niloticus)

Abstract

This study evaluated whether the resting density after transport in Nile tilapia Oreochromis niloticus shows responses in the respiratory and ionic dynamics related to stress parameters. Forty specimens were submitted to four experimental treatments consisted of control (minimum stress/after removal from water), after transport and one hour of rest, in two stocking densities (50 and 300 kg of live weight)/m3), with 10 repetitions per treatment. Each fish was considered an experimental unit. Serum stress was evaluated by measuring the glucose and lactate levels, and respiratory dynamics were determined by measuring ionic concentration. The fish in the group after transportation remained in hypoventilation due to high PCO2 values, demonstrating compensatory respiratory acidosis. The stress level was high, indicating increased glycemia. The group of fish in the 300 kg/m3 density remained in respiratory acidosis. No change in lactate was observed in any of the resting densities. It is concluded that the 50 kg/ m3 density is suitable for pre-slaughter rest because it results in fish with reduced stress responses and with reestablished respiratory responses.