Abstract:This study investigated the resistance and related physiological changes in response to high water temperature of the new breed (Gaokang No.1) sea cucumber Apostichopus japonicus for a period of 3 years, using ecological, histological and digestive enzyme assays. The results showed that for year 2013, 2014 and 2015, “Gaokang No.1” sea cucumber entered into aestivation at the aestivation temperature (AT) of 29.13℃, 30.47℃ and 29.68℃, respectively, and finished aestivation at the released aestivation temperature (RAT) of 24.55℃, 24.94℃ and 24.16℃, correspondingly. While the AT of the sea cucumber in the non-selected group was 27.08℃, 28.61℃ and 27.93℃, and the RAT was 21.33℃, 21.83℃ and 22.06℃, respectively. Compared with the non-selected sea cucumber, the aestivation critical temperature (ACT) of “Gaokang No.1” breed increased by 1.89℃, and aestivation lifted critical temperature (ALCT) increased by 2.81℃. Hence, the average aestivation period was shortened about 26.7 days a year. The intestine of sea cucumber was severely degraded after aestivation, with characteristics of atrophy, reduced length and width, dark color, and no food in the intestine. Also the intestinal chorionic abundance decreased and the intestinal ridge height was reduced to about 140 μm. The respiratory tree became atrophy in size. By comparison, when the aestivation released, sea cucumber restored to the normal intestinal length; the intestinal chorionic abundance increased significantly and the intestinal ridge height increased to about 640–660 μm. In addition, the amylase and trypsin activities tended to decrease as the water temperature increased for both “Gaokang No.1” breed and the non-selested sea cucumber. Both enzyme activities increased significantly as the aestivation released. However, the enzyme activities were higher among “Gaokang No.1” breed compared to the non-selested sea cucumber under the same rearing temperature. Compared to the non-selested sea cucumber, the “Gaokang No.1” breed can tolerate high temperature, therefore extended the production period for nearly a month. The results indicated the “Gaokang No.1” sea cucumber is a better breed in terms of high temperature resistance and shows improved survival rate and productivity. The study provides a technical reference to health management and seed production in sea cucumber culture.
