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.