Abstract:The effects of two factors (temperature and diet) on the gonadal development and quality of the resulting offspring of sea cucumber (Apostichopus japonicus) were examined in this study. Two temperatures (12℃ and 15℃) and three diets (50% Sargassum thunbergii Kuntze powder + 50% sea mud, 50% Laminaria japonica powder + 50% sea mud, and 25% S. thunbergii Kuntze powder + 25% L. japonica powder + 50% sea mud) were tested through single factor experiments. In addition, changes in the biochemical composition of the body wall during conditioning and biochemical composition of the female gonad after conditioning in different treatments were also quantified. Sea cucumbers were maintained in seawater, which was changed daily and provided with aeration, and were fed at a daily ration equivalent to 5%~10% of their dry biomass. Three replicate tanks were assayed for each treatment. Gonad index and spawning rate of female animals, egg diameter, fertilization rate of eggs, hatching rate of larvae, and body length of early auricularia were also evaluated. The results of the temperature treatments revealed that spawning rate, gonad index, and fecundity of females were significantly affected by temperature, and significantly higher at 15℃ than that at 12℃ (P<0.05). In the diet treatments, there were no significant differences in gonad index, spawning rate, and fecundity of females among the three groups; however, the mixed algae powder group showed the highest values. Hatching rate of embryos and body length of early larvae in the mixed algae powder group were significantly greater than that in the L. japonica powder group. The results indicated that egg quality was the best in a broodstock supplied with mixed macroalgae powder and sea mud. Biochemical analysis of the body wall revealed that carbohydrate levels in the A. japonicus body wall declined during conditioning, supporting the theory that carbohydrates are mobilized to provide energy or precursors for lipid or protein synthesis in the gonad.
