Mating behavior and the effects of low salinity on the reproductive performance of Eriocheir sinensis H. Milne-Edwards, 1853 (Decapoda: Brachyura: Varunidae)

Salinity is a key factor affecting the behavior and reproduction of Chinese mitten crabs (Eriocheir sinensis H. Milne-Edwards, 1853). We investigated the effects of low salinities on the mating behavior and the breeding performance of the species using infrared cameras. Mating and spawning experiments were set up under different salinities (0 ppt, 2 ppt, 4 ppt, 6 ppt, 8 ppt), with each treatment having three parallel groups, each stocked with five males and ten females. Reproductive performance indicators such as gonadosomatic index (GSI), hepatosomatic index (HSI), mating and spawning rates, egg production, reproductive index, and fecundity were analyzed. The results revealed that mating can be divided into five distinct stages: probing, pairing, mating, guarding, and separation. Two mating postures were identified: traditional and upright mating. Salinity had a significant impact on mating rates and the time to first pairing, the highest mating rate was observed at 8 ppt, reaching 90 ± 9.55%, with the shortest time to first mating at 1 ± 0.62 h. While crabs could pair at salinity 0, mating did not occur. Female crabs mated but failed to spawn at 2 ppt and 4 ppt. At 2 ppt, the mean mating rate was significantly lower (20 ± 14.14%) compared to 4 ppt, 6 ppt, and 8 ppt (P < 0.05). The minimum salinity required for spawning was 6 ppt, with no significant differences in spawning rates, egg production, reproductive index, or fecundity between 6 ppt and 8 ppt (P > 0.05). Although the HSI of females was the highest at 8 ppt, no significant differences were observed between different salinities (P > 0.05). The GSI of females was the highest and significantly higher at 4 ppt (P < 0.05). The investigation provides precise duration values for mating behavior in E. sinensis and enhance our understanding of reproductive investment in the species.