Effect of temperature fluctuation on the physiological stress response of hybrid pearl gentian grouper during waterless keeping alive

Temperature fluctuations are inevitable and have an important impact on the survival of fish during transportation. Therefore, the effect of temperature fluctuation (15 ± 1 °C, 15 ± 2 °C, 15 ± 3 °C) on the muscle quality, physiological, and immune function of hybrid pearl gentian grouper before waterless keeping alive, during keeping alive (0 h, 3 h, 6 h, 9 h, 12 h), and after revival for 12 h was investigated. The plasma glucose concentration of grouper gradually decreased to 0.645 ± 0.007 mg/mL, 0.657 ± 0.006 mg/mL, and 0.677 ± 0.004 mg/mL after keeping alive for 12 h under different temperature fluctuations of 15 ± 1 °C, 15 ± 2 °C, and 15 ± 3 °C, respectively. The cortisol concentration and lysozyme activity of pearl gentian grouper significantly increased ( P < 0.05) during the keeping alive period. The results suggested that fish bodies would produce acute stress response, strengthen immune defense ability, and quickly consume a lot of energy to adapt to the low-temperature anhydrous environment. In all treatment groups, the activities of plasma alanine transaminase (ALT) and aspartate aminotransferase (AST) and the content of creatinine gradually increased with the prolongation of the survival time. The hardness and springiness of muscle decreased from 5965.99 ± 20.15 and 0.90 ± 0.00 to 3490.69 ± 27.59 and 0.42 ± 0.01, respectively. In the meanwhile, the change of glycogen and lactic acid content was opposite, indicating that temperature fluctuation harmed the liver, kidney function, and muscle quality. In the later stage of keeping alive, the superoxide dismutase (SOD) and catalase (CAT) activities decreased, especially in the temperature fluctuation group of ±3 °C (125.99 ± 5.48 U/mgprot, 44.21 ± 0.63 U/mgprot), leading to an imbalance of fish immunity. In summary, higher temperature fluctuation would influence the physiological function and immune defense ability and decrease the quality of pearl gentian grouper.