Metabolic and anti-oxidative stress responses to low temperatures during the waterless preservation of the hybrid grouper (Epinephelus fuscogutatus♀ × Epinephelus lanceolatus♂)

Waterless transportation is an alternative method of live aquatic product transportation, which may reduce shipping costs and increase the survival rates of some species. Groupers are economically important fishes that are widely cultivated in Asian countries. However, the waterless transportation of live groupers has yet to be studied. A key to the success of live waterless transportation is the preservation temperature, which needs to be empirically determined for each species. The hybrid pearl gentian grouper (♀E. fuscogutatus × ♂E. lanceolatus) has become the main farmed grouper species in China due to its superior growth performance. In this study, we investigated the effects of temperature on the survival, metabolism, and oxidative stress responses of the pearl gentian grouper during waterless preservation after cold-induced dormancy. Our results showed that the grouper survival duration was 10 h at 15 °C and 18 °C, twice as long as the survival duration at 13 °C and 25 °C (5 h). Levels of serum cortisol, as well as the activity levels of the metabolic enzymes aspartate amino transferase (AST), alanine amino transferase (ALT), acid phosphatase (ACP), and alkaline phosphatase (AKP), were not significantly different between the untreated fishes and the fishes preserved without water for 5 h at 15 °C and 18 °C. In addition, the activity levels of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) in liver and brain tissues of the waterless-preserved fishes were significantly higher than the untreated fishes, while the malondialdehyde (MDA) content was decreased. In the waterless-preserved fishes, blood glucose levels were increased 15.32-fold at 15 °C and 10.99-fold at 18 °C, as compared to the untreated fish, while muscle lactate levels were reduced by 28.21%. There were no significant differences in the levels of free amino acids in the muscle between the untreated and waterless-preserved fishes. Therefore, waterless preservation at 15 °C or 18 °C improved the survival of the pearl gentian groupers by stimulating antioxidant enzyme activity and increasing serum glucose levels. Our study represents the first successful application of waterless preservation techniques to live groupers, sufficient for medium or long distance transportation.