Effect of Temperature Lowering Rate on Physiological Response of Oplegnathus punctatus in Live Fish Chill Preservation

  Objective  Physiological response of Oplegnathus punctatus to the rate of temperature lowering was studied to optimize the live fish chill preservation technology for water-conservation transportation.

  Method  Live and healthy O. punctatus were chilled at a rate of 1, 3, or 5 ℃·h⁻¹ from 17.5–18.5 ℃ to the critical dormancy temperature of 10 ℃. Kept the fish out of water, in intervals of 0, 2, 4, and 6 h, sampling for the determination of various physiological indicators was conducted for a data analysis.

  Result  The highest survival rate of O. punctatus in 6 h after the treatments was 76.7% with a chilling rate of 3 ℃·h⁻¹. Under the chilling and low-temp preservation, the contents of cortisol, AST, ALT, MDA, GLU, and LAC in the fish of all treatment groups increased significantly (P＜0.05), while those of EPI, hepatic glycogen, and muscle glycogen significantly declined (P＜0.05). The serum indices of the fish chilled at all 3 rates for 6 h at 10 ℃ changed significantly (P＜0.05). The contents of EPI, cortisol, liver ALT, and hepatic glycogen were significantly higher under the 1 ℃·h⁻¹ than the 3 ℃·h⁻¹ or 5 ℃·h⁻¹ treatment (P＜0.05) indicating a stronger stress response of the fish by the temperature lowering rate at 1 ℃·h⁻¹ than the other two; while AST, MDA, and LAC were significantly higher under the 5 ℃·h⁻¹ than the 1 ℃·h⁻¹ or 3 ℃·h⁻¹ treatment (P＜0.05) and EPI, AST, ALT, MDA, LAC, and hepatic glycogen significantly lower under the 3 ℃·h⁻¹ than the 1 ℃·h⁻¹ or 5 ℃·h⁻¹ treatment (P＜0.05) showing the 3 ℃·h⁻¹ rate of chilling minimized the effect of cold stress and lessen the liver injury on O. punctatus in the preservation process.

  Conclusion  It appeared that a temperature lowering rate, such as 3 ℃·h⁻¹, could be a tolerable threshold for the fish to make adequate acclimation to recover from physiological ill-effects with a high survival rate out of water at 10 ℃ for 6 h.