The spotted halibut is species that has a high potential market value in Korea, but the supply of seed is unstable because of the limited milt production of males. The objective of this research was to explore different aspects, such as CPAs, diluents, dilution ratio, and freezing rates, to develop an optimal sperm cryopreservation. The parameters assessed were movable sperm ratio, sperm activity index, survival rate, and DNA damage. The CPAs tested in this research were propylene glycol, dimethyl sulfoxide (DMSO), methanol, ethylene glycol, and glycerol. Different diluents, including 300 mM sucrose, 300 mM glucose, Stain’s solution, and Ringer’s solution, were investigated. The previous experiment showed that the optimal CPA for cryopreservation was DMSO with a concentration of 15% with 300 mM as diluent. To determine the effect of the dilution ratio, sperm was diluted to 1:1, 1:2, 1:10, 1:100, and 1:1000 with 300 mM sucrose containing DMSO at a final concentration of 15%. Lastly, the optimal freezing rate of the sperm was evaluated with four different freezing rates (−1, −5, −10, and −20 °C/min). Post-thaw sperm motility was higher with a dilution ratio lower than 1:2, and the freezing rate was less than −5 °C/min. In conclusion, these findings represent the development of a cryopreservation protocol for spotted halibut.

The Pacific abalone (Haliotis discus hannai) is the most economically valuable shellfish species in Northeast Asia, accounting for most of the shellfish production in South Korea. Despite the continuous improvement in the productivity of domestic abalone aquaculture, rapid seawater temperature changes caused by global warming have led to mass mortality in coastal abalone farms. Therefore, research on environmental stressors is urgently needed to prevent abalone production losses. This study analyzed the expression of heat shock protein (HSP) genes in foot muscles of H. discus hannai and metabolic parameters including glucose, lysozyme, catalase, D‐lactate, and trehalose levels in the hemolymph under acute high temperature, low temperature, low salinity, and air exposure. Quantitative reverse‐transcription polymerase chain reaction analysis showed that HSP20 expression was downregulated in all experimental groups, whereas HSP70 expression increased immediately in all experimental groups except for the low‐temperature stress group. Hemolymph analysis showed that glucose and lysozyme levels increased significantly immediately after treatment in all groups, and decreased during the recovery period. Together, the results indicate that low water temperature stress had the smallest effect on abalone among the treatments. We conclude that the other treatments acted as stressors of abalone and that HSP genes, glucose, and lysozyme can be used as stress indicators in H. discus hannai.

Water temperature is the most important factor in fish farming as changes in water temperature cause physiological stress in fish. There have been few studies on physiological responses to high temperatures, which vary with aging. This study investigated the responses of juvenile and adult Platichthys stellatus to heat stress. Plasma cortisol, glucose, lactate, and lysozyme levels, antioxidant enzyme activities, and expression of heat shock proteins 70 and 90 (HSP70 and HSP90) of P. stellatus were determined at water temperatures of 16, 20, 24, 28, and 30°C. As a result, it was confirmed that several plasma parameters of adult were significantly higher than that of juvenile under heat stress. Plasma cortisol and glucose levels of adult were increased than juvenile at 24 and 28°C. Plasma lactate level of adult were higher than that of juvenile at 28°C. Comparisons of survival and physiological changes showed that juveniles have better thermal tolerance, resulting in a higher cumulative survival rate. Moreover, the relationship between thermal tolerance and HSP gene expression revealed that expression of HSP70 and HSP90 was significantly upregulated at 28°C in both juvenile and adult fish, and HSP70 expression was significantly higher in juvenile fish than in adult fish. It is judged that the adult’s HSP70 activity was lower than juvenile, so the demand for plasma parameters for heat response was relatively high, whereas juvenile’s HSP70 activity increased at 24 and 28°C, indicating a relatively stable value of plasma parameters. These results indicate that the thermal tolerance of juvenile fish is greater than that of adult fish, based on the differences in plasma parameters and HSP expression. These findings improve our understanding of age-related changes in P. stellatus during thermal stress and may help guide the management of fish farms.

Fisheries and Aquatic Sciences