Physiological Responses of Intrinsic Small Abalone Haliotis diversicolor aquatilis under High Temperature Stress by Low Level 60CO Gamma Irradiation-Mediated Hormetic Effect

Haliotis diversicolor aquatilis (H. diversicolor aquatilis) is one of the aquaculture abalone species in Jeju Island, South Korea. The high water temperature in the middle of the summer season frequently limits the aquaculture productivity of abalone. To cope with the problem, this study aimed to investigate viability, attachment rate, changes of immune response, and physiological properties of juvenile small abalone Haliotis diversicolor aquatilis against high water temperature stress under 60CO-gamma irradiation-mediated hormetic effects. To examine physiological changes of abalone, the gamma-ray irradiated and non-irradiated groups were distinguished by grouping a total of 70 abalones in a treated group and a control group (each group included twenty-five female and ten male abalones). The treated group was exposed to 60CO-gamma irradiation using a designed experimental apparatus, the control group was not. Our results revealed that the low level of gamma ray (20 Gy)-irradiated Haliotis diversicolor aquatilis showed a 100% survival rate during the experiment. After gamma ray exposure, all the abalones were cultured without feeding and bioactivities were measured to examine gamma ray-induced physiological responses. The results suggested the potential for selective breeding using gamma ray irradiation hormesis to manipulate the number of eggs, fertilization rate, hatching rate, and attachment rate. The shell length of juvenile abalone was significantly enhanced by a 20 Gy radiation dose. We could presume that the effect of hormesis in the gamma-ray irradiation parent shellfish also had a genetic effect on the offspring. In order to verify changes in immune response and stress tolerance of abalone under high temperature stress, lysozyme activity and survival rates were compared at a water temperature of 30 °C. Interestingly, the 60Co gamma ray-irradiated abalones exhibited almost a 1.65-fold enhanced survival rate along with reduced lysozyme activity after 12 h of high temperature stress. Our results speculate that low levels of 60Co gamma ray-mediated hormetic effects can be an effective strategy for shell length growth and high temperature stress tolerance.