At present, the resources of anadromous fish in the world are drastically reduced and one of the solutions to promote its recovery may be to identify and protect its feeding grounds. To determine whether the feeding grounds of anadromous Coilia nasus in the Yangtze River are still in the sea area, the quantitative line analysis of Sr and Ca contents (Sr/Ca ratios) and the area distribution analysis of Sr content in the otoliths of C. nasus in three water areas (Poyang Lake, Yangtze River estuary and Shengsi Sea area) were carried out by electron probe microanalysis (EPMA) to analyze the habitat use and the migratory patterns of different estuarine C. nasus. These results showed that the Sr/Ca ratios of all otoliths fluctuated significantly. By comparison, it was found that C. nasus of Yangtze River might exist in the Shengsi Sea area, and the Shengsi Sea area might be one of the feeding grounds of migratory C. nasus. Therefore, it is urgent to carry out a comprehensive investigation on the distribution of related groups in the Shengsi Sea area and the influence of potential threat factors, such as fishing and harsh habitat, to effectively protect the resources and habitats of C. nasus in the Shengsi Sea area.

A shelter is a good habitat for aquatic organisms, which could aid in avoiding cannibalism and facilitate predation. Chinese Mitten Crab (Eriocheir sinensis) is an important aquaculture species with troglodytism and nocturnal habit. To clarify the preference for shelters at different developmental stages of E. sinensis, different shelters (mud, sand, grass and rocks) were selected for comparison. These results indicated that juvenile crabs had a significant preference for grass; button-sized crabs preferred to hide in mud; and the favorite shelters for parent crabs were rocks, followed by mud. E. sinensis in three stages all showed concealing behavior. The concealing behavior of juvenile crabs was the most significant, followed by button-sized and parent crabs. Additionally, E. sinensis held a low hiding rate at night but a high hiding rate during the daytime due to nocturnal habits. These findings will help to better understand the habits of E. sinensis and provide a reference for resource restoration, habitat construction and the restoration of E. sinensis.

Procambarus clarkii is adept at using natural shelters and caves to evade attacks from predators. However, the concealment abilities and mechanisms of P. clarkii for different types of shelters under predation pressure have not yet been reported. In this study, laboratory experiments were carried out to determine the effects of different coverages (25%, 50%, and 75%) and different combinations (I–VII) of three types of shelters (PVC pipes, water grass, and stone) on the predation rhythm, behavior, and abilities of Silurus asotus on P. clarkii. The results indicated that the predation of S. asotus on P. clarkii exhibited significant rhythmicity under shelter conditions, excluding PVC pipes, 75% stone, and combination VI. Among the three types of shelters, PVC pipes provided the strongest concealment, followed by stone and water grass. With the increase in shelter coverage, the anti-predation ability of P. clarkii continued to increase, and the optimal shade rate for water grass was 50%. In the different shelter combinations, the environmental complexity had little effect on the predation activity of S. asotus on P. clarkii. These findings demonstrated that the type and abundance of shelters in the wild environment can affect the predation rhythm and activities of S. asotus on P. clarkii.

The effects of salinity on behavior are far-reaching, and Eriocheir sinensis showed disparate behaviors under different salinity conditions. Female crabs were more active in saline water, especially low salinity stress, which is beneficial for female crabs to escape from the low-salinity environment quickly. Then, antennal movement indicated that antennae might be the main osmoreceptors in E. sinensis, and 65 min might be a good starting time for salinity stress to analyze osmoregulation in crabs. Interestingly, E. sinensis had obvious behavioral differences in the high and low salinity stress, and behaviors were more intense in a salinity dip from salinity 18 to salinity 0. This study analyzed the osmoregulatory process of catadromous E. sinensis in different salinity from the point of osmoregulatory organ and behavioral response. These results will provide a scientific basis for the osmoregulatory mechanism of E. sinensis, which are conducive to evaluating and analyzing the impact of saltwater intrusion in the Yangtze River estuary on resource fluctuation.

Background: Scatophagus argus is a euryhaline fish, but the molecular mechanism of salinity plunge response on liver antioxidant system of S. argus is currently poorly understood. Meanwhile, the transcriptome is a powerful tool for studying the effect of stress on physiological mechanisms. Transcriptome analysis of juvenile S. argus in salinity slump will provide a reference for future research on the stress resistance of S. argus. Methods: 5 ppt was selected as low salinity and 20 ppt was used as the control group. The experimental treatment time was 6 h. Liver samples were separately obtained for transcriptome sequencing. Transcriptomic data of the liver after salinity plunge for 6 h were analyzed. Result: 474 differentially expressed genes were generated by the sudden change of salinity. The pathways related to immune defense were enriched, such as ‘Antigen processing and presentation’ and ‘Phagosome’, implying that S. argus might enhance the immune defense system. Several antioxidant enzyme genes, such as HAO, Trx, PHGPx, were up-regulated to resist oxidative stress caused by low salinity. The down-regulation of Cul3 also might promote the activation of Nrf2 to activate the expression of antioxidant enzyme genes. These results indicated that S. argus initiated a molecular mechanism to resist low salt stress.