Effects of dissolved oxygen on behavior, reproductive characteristics and embryo quality of Eriocheir sinensis

In order to find out the effects of dissolved oxygen (DO) on the reproductive performance and the embryo quality of female Chinese mitten crab Eriocheir sinensis broodstock, mating and spawning experiments were carried out with different levels of DO (5 mg/L, 6.5 mg/L, 8 mg/L, 9.5 mg/L, 11 mg/L, 12.5 mg/L). Three parallel tanks were set up for each DO condition and each tank was stocked with 5 male and 10 female crabs. The results showed that with the increase of DO levels, the mating rate of broodstock crabs gradually increased, the spawning rate, spawning capacity, fecundity and reproductive index first increased and then decreased. The above four indicators peaked at a DO level of 11 mg/L, showing significant differences from all other groups ( P < 0.05). In both the 5 mg/L group and the DO sudden drop group (from 12.5 to 5 mg/L), the Chinese mitten crabs were observed to exhibit significant standing behavior, along with a marked increase in the frequency of mouthpart activity and appendage movement. The occurrence rates of the above three behaviors showed significant differences compared to all other groups ( P < 0.05). In the 6.5 mg/L and 12.5 mg/L DO groups, the locomotor activity frequency of the crabs was relatively high and significantly higher than that in the other groups ( P < 0.05). At a DO concentration of 9.5 mg/L, the embryonic diameter of the Chinese mitten crab peaked and was significantly higher than that of all other groups ( P < 0.05). As the DO concentration increased, the phospholipid content in the embryos gradually increased, while the total lipid content gradually decreased. Changes in ash and moisture content were not significant. Crude protein, total cholesterol, and triglyceride levels initially increased and then decreased, peaking at 9.5 mg/L. The study confirmed that DO levels significantly influence the reproductive performance and embryonic quality of the Chinese mitten crab, broodstock had the best reproductive performance at 11 mg/L DO, while embryonic quality was relatively better at 9.5 mg/L DO. The research findings not only provide a basis for the artificial breeding of the Chinese mitten crab but also offer scientific support for the conservation of fishery resources in the Yangtze River Estuary. • Dissolved oxygen significantly affects reproduction and embryo quality in Eriocheir sinensis. • Optimal spawning performance at 11 mg/L dissolved oxygen. • Highest embryo quality observed at 9.5 mg/L dissolved oxygen. • Hypoxia induces abnormal behaviors like prolonged standing and mouthpart activity. • DO levels regulate embryonic lipid and fatty acid composition.