| The Chinese mitten crab (Eriocheir sinensis) is an economically important species in China, and its reproductive performance and embryo quality are particularly important for the quality of newly hatched larvae. E. sinensis is a weak crustacean thermoregulator. From November to May every year, broodstock crabs complete mating, spawning, and early larval development in the Yangtze River Estuary. During this period, they become more sensitive to environmental changes. Water temperatures that are too low or high have direct or indirect effects on the breeding of E. sinensis. Therefore, temperature is an important environmental factor affecting the breeding of E. sinensis. To explore the effects of temperature on the reproductive performance and embryo quality of female E. sinensis, reproduction and oviposition experiments of parent crabs at different temperatures (6 ℃, 9 ℃, 12 ℃, 15 ℃, 18 ℃, and 21 ℃) were conducted. Three parallel groups were set up for each temperature, and three samples were collected for each parallel group. The reproductive performance of females at different temperatures, such as mating rate, spawning rate, spawning volume, and fertility, and the quality of the embryos produced, such as egg diameter, dry weight of a single egg, and wet weight of embryos, were analyzed through observation and calculation. The crude protein content of embryos was determined using the Kjeldahl method; the total fat content was determined using acid hydrolysis; the composition and content of fatty acids were detected using gas chromatography; the moisture content of embryos was determined by taking 2–3 mg of wet embryos from each temperature group and drying them at 70 ℃ until constant weight; the ash content was determined by burning them at 550 ℃ until a constant weight; and the triglyceride, phospholipids, and cholesterol contents were determined using an enzyme immunoassay kit. The results showed that (1) with an increase in temperature, the mating rate of parent crabs increased gradually, and the spawning rate, spawning capacity, fecundity, and reproductive index first increased and then decreased. When the temperature was 15 ℃, the spawning rate, spawning capacity, fecundity, and reproductive index of female crabs were the highest, with averages of (80±10)%, (15.38±1.81)×104 grains/only, (0.23±0.03)×104 grains/only, and (20.01±1.59)%, respectively. There were significant differences with other temperature groups (P<0.05). (2) At 18 ℃, the egg diameter of the embryos was the largest, with an average of (431.17±13.69) μm. At 15 ℃, the dry weight of a single embryo was the heaviest, with an average of (31.28±4.61) μg; however, there was no significant difference between the 15 ℃ and 18 ℃ groups (P>0.05). (3) With an increase in temperature, the ash and phospholipid contents of the embryos increased gradually, whereas the total fat content decreased gradually. Triglyceride and total cholesterol contents first increased and then decreased, whereas crude protein and water contents did not change significantly. The crude protein, triglyceride, and total cholesterol contents in embryos were the highest at 18 ℃, with an average of (20.83±1.72)%, (26.2±0.71) μmol/g, and (97.3±1.19) μmol/g, respectively. (4) Twenty-one fatty acids were detected in the E. sinensis embryos, of which saturated and monounsaturated fatty acids were the highest at 12 ℃; however, there was no significant difference with other groups (P>0.05). The total contents of C20:5n3 (EPA), C22:6n3 (DHA), C20:4n6 (ARA) and polyunsaturated fatty acids in embryos at 6 ℃ were the highest, with an average of (4.26±0.85) mg/g, (4.93±0.79) mg/g, (2.96±0.44) mg/g, and (22.74±3.22) mg/g, respectively. This study showed that temperature had a certain effect on the quality of embryos produced by Chinese mitten crab, and its reproductive performance was the best at 15 ℃. This study provides basic data for the study of the breeding biology of E. sinensis and scientific support for the conservation of fishery resources of E. sinensis in the Yangtze River estuary. |
