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Understanding the physiological changes of oocyte in vitro maturation are important for improving in in vitro fertilization rates and embryonic development. In this study, Apostichopus japonicus gonads were dissected, and the oocytes and gonadal fluid extracted from the gonads were dried in darkness to induce oocyte maturation. The changes in the germinal vesicle breakdown percentage (GVBDP), superoxide dismutase (SOD) activity, and the concentrations of glutathione (GSH), cyclic adenosine monophosphate (cAMP), adenylyl cyclase (AC), protein kinase C (PKC), oestradiol (E2), and metabolites in gonadal fluid–oocyte complexes (GFOC) were detected during desiccation. The GVBDP peaked at 85% after 2 hr of desiccation. The SOD activity and GSH concentration in GFOC increased significantly during desiccation, reaching their maximum values at 0.5 and 2 hr of desiccation respectively (p < 0.05). The concentrations of cAMP, AC, PKC, and E2 decreased significantly during the desiccation treatment (p < 0.05) and reached relatively stable levels after 1 hr of desiccation. After 2 hr of desiccation, among the 68 metabolites detected in the GFOC, the concentrations of 52 metabolites increased and those of 16 metabolites decreased. This study not only provides an effective and simple technique for in vitro induction of A. japonicus oocyte maturation under desiccation stress, but also improves our understanding of gamete biology in this species. [ABSTRACT FROM AUTHOR]

Abstract: Two groups of Apostichopus japonicus, a thermotolerant strain (group G3: wet weight, 64.22 ± 13.16 g/ind.), which was selected focusing on the performance of thermo‐tolerance through three generations for 10 years, and a control group (group C: wet weight, 62.08 ± 12.01 g/ind.) were collected from July to October in a seawater pond in northern China. Differences in relative faecal mass (RFM), relative intestinal mass (RIM), percentage of individuals with faeces (PIWF) and intestinal metabolites were investigated and compared between the two groups. The temperatures of terminating aestivation of the two groups were assessed according to the values of RFM and RIM. A regression analysis showed that the corresponding group G3 temperatures were 0.56–1.34°C and 0.70–1.49°C higher than those of group C when RFM and RIM were 0.01–0.05 and 0.005–0.025 respectively. The PIWF values in group G3 were 11.5%–21.2% higher than that in group C from 20 July to 22 September. Significant differences at the concentrations of 52 metabolites were detected between the two groups, 36 were higher in group G3 and 16 were higher in group C. The concentrations of threitol, 2‐methylglutaric acid, N‐acetyl‐D‐galactosamine, N‐acetyl‐L‐leucine, lactose, oxoproline, 2,3‐dimethylsuccinic acid and d‐glucoheptose were significantly different between groups G3 and C and were considered metabolic markers distinguishing group G3 from group C. Metabolism of A. japonicus in group G3 was more active than that in group C. These results provide new insight for understanding ingestion and intestinal metabolism in the thermotolerant strain of A. japonicus under high summer temperature. [ABSTRACT FROM AUTHOR]

We evaluated the effect of rearing density on the yield of a fast-growing and heat-resistant strain of Apostichopus japonicus using a full-sib family. We analysed the relationship between density and key growth parameters during factory seedling of A. japonicus and developed a model to explain the variation in growth. From 130 to 220 days, the rearing density of A. japonicus had a significant effect on body weight, specific growth rate, coefficient of variation and survival rate ( P < 0.05). We obtained predicted integral regression equations for yield and growth rate, density fluctuation, variable coefficient fluctuation and survival rate. Specific growth rate had a significant effect on the yield of A. japonicus and, therefore, can be used as a primary indicator of yield. We recommend that stocking density should be adjusted from age 130-166 days to avoid frequent seedling separation to different pools of different seedling sizes during the fast growth period of A. japonicus seedlings, a procedure that causes yield decline. The optimal initial stocking density was 24.4 g m−2 (0.2 g L−1). [ABSTRACT FROM AUTHOR]

We evaluated the effect of high temperature on Apostichopus japonicus gametes. Gametes were exposed to the optimal temperature (18°C; control) or one of six high temperature treatments (26, 27, 28, 29, 30 and 31°C) and the cleavage rate ( CR) of fertilized eggs was measured as an indication of fertilization ability. At control temperatures (18°C), the male and female gametes had high fertilization ability ( CR ≥95.0%) in 5 h and the time at which 50% of gametes lost the ability to successfully fertilize ( LT50) was 7.03 h. All gametes were non-viable after 9 h. When male and female gametes were both exposed to high temperature, the LT50 was lower than that when female or male gametes were treated individually at the same high temperature ( P < 0.05). The LT50 was lower for male gametes treated alone than for female gametes treated alone. In conclusion, exposure to high temperature results in a decline in fertilization ability of A. japonicus gametes, and this decline was more rapid at higher temperature. The female gametes were more resistant to high temperatures than male gametes. [ABSTRACT FROM AUTHOR]