Water quality and physiological response of F1 hybrid seabream (<italic>Pagrus major</italic>♀ × <italic>Acanthopagrus schlegelii</italic>♂) to transport stress at different densities.

Abstract: Hybrid seabream (<italic>Pagrus major</italic>♀ × <italic>Acanthopagrus schlegelii</italic>♂) grow quickly, with retarded gonadal growth and enhanced muscle nutritional composition. This F1 hybrid seabream is a new marine aquaculture fish in China. However, the response of hybrid seabream to transport is severe, which seriously restricts its promotion and development. Water quality and the physiological response of hybrid sea bream were studied at three fish transport densities (5, 10 and 20 g/L) during 8 hr of transport in a light van (60 km hr−1 and 25°C water temperature). We found that total ammonia–nitrogen and nitrite–nitrogen levels in the water of the highest density group increased sharply after 4 and 8 hr of transport. Cumulative survival of the fish in the 10 and 20 g/L groups (86.7% and 75% respectively) was significantly lower than in the 5 g/L group (100%) after 8 hr of transport (<italic>p </italic><<italic> </italic>.05). Serum cortisol and lactate levels were significantly higher after transport than pre‐stress levels, whereas the glucose level decreased significantly (<italic>p </italic><<italic> </italic>.05). Hepatic triglyceride and glycogen levels and superoxide dismutase and catalase activities were significantly lower in the 20 g/L group than in the 5 g/L group (<italic>p </italic><<italic> </italic>.05). The results show that high‐density transport increased ammonia–nitrogen and nitrite–nitrogen levels in the water as well as cortisol secretion and anaerobic metabolism in the F1 hybrid seabream, suggesting that total cholesterol and glycogen may be used to supply the energy demand and increased oxidative stress. These results will help to optimize the transport conditions for cultured hybrid seabream. [ABSTRACT FROM AUTHOR]