The effects of MS‐222 and clove oil on blood biochemical parameters of juvenile Siberian sturgeon (Acipenser baerii) were studied. MS‐222 caused higher glucose (GLU) concentrations in anaesthetic test groups than for the control group. Triglyceride (TGL) concentrations of fish in the 140 and 160 mg L⁻¹ groups were also significantly higher than those of other groups. Alanine aminotransferase (ALT) activity in the 140 mg L⁻¹ group was significantly higher than the level in 80, 100 and 120 mg L⁻¹ groups. Aspartate aminotransferase (AST) activity in the 140 mg L⁻¹ group was significantly higher than those in the 100 and 120 mg L⁻¹ groups. Levels of total protein (TP), cholesterol (CHOL) and alkaline phosphatase (ALP) in anaesthetic test groups were not significantly influenced by MS‐222. Clove oil did not have significant effects on levels of GLU, TP, CHOL, ALT and ALP. TGL concentration of fish exposed to 180 mg L⁻¹ clove oil was significantly higher than those of the rest anaesthetic groups. AST activities of fish exposed to 120, 150 and 180 mg L⁻¹ were significantly higher than those of 60 and 90 mg L⁻¹. Overall, TGL and AST could be potentially used as indicators of anaesthetic stress for juvenile Siberian sturgeon. Based on blood biochemical parameters, the appropriate anaesthetic concentrations of MS‐222 and clove oil were 80–120 mg L⁻¹ and 60–90 mg L⁻¹, respectively. Clove oil was a promising alternative to MS‐222.

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.

To understand the metabolic adjustments and nitrogen excretion in haemolymph of mature Eriocheir sinensis during the reproductive migration from fresh water to seawater, haemolymph metabolic variations and nitrogenous wastes were determined after gradual acclimation of females and males from fresh water to different salinities (7, 14, 21, 28 and 35). Total protein content in both female and male crabs was reduced with increased salinity. The contents of lipids including triglyceride and cholesterol significantly decreased at salinities of 0-21, suggesting the lipids of E. sinensis might be mobilized to produce energy for osmoregulation and gonad development at a different salinity. Interestingly, the lipid levels in the females were higher than those in the males, implying the females need to store more lipids to prepare for reproduction. The glucose level was low in this study, which was related to the diet with high protein. Haemolymph urea and uric acid level together decreased at first and then increased, indicating that E. sinensis could regulate the nitrogen excretion pattern by inhibiting or activating ureogenesis and uricogenesis to acclimate to a different osmotic environment. Notably, the females might be more tolerant to salinity increase and have a faster metabolic reorganization than males. These facts could indicate that a different strategy has been employed in mature E. sinensis when encountering salinity stress during the reproductive migration form fresh water to seawater.

Background: The Chinese mitten crab (Eriocheir sinensis) is widely distributed in the coastal and coastal water of China and has important economic values. Salinity is the key environmental factor affecting the mating and spawning of E.sinensis. During the mating and spawning of E. sinensis, the hormone changes in the body are usually accompanied, but there is no report about the effects of salinity on related hormones in the process of breeding of E. sinensis. Methods: Mating salinity including 0‰, 2‰, 4‰, 6‰ and spawning salinity such as 3‰, 6‰, 9‰, 12‰, 15‰, 18‰, 21‰ were set up, three parallel groups are set for each salinity, 10 female and 5 male crabs are put in each tank. 5 samples were gathered to analyze the contents of 17α,20β-dihydroxy-4-pregnene-3-one (DHP), Gonadotropin (GTH), Prostaglandins (PG), Estradiol-17β (E2) and Testosterone (T) in the hemolymph of female E. sinensis after mating and spawning. Result: The contents of DHP, E2, PG and T in female crabs hemolymph decreased first and then added with the increase of salinity before spawning. DHP, PG and E2 added first and then declined with the increase of salinity after spawning. When salinity was 6‰, the contents of DHP, PG, E2 and T in the hemolymph of female crabs before spawning reached the highest, the contents of DHP and PG decreased and E2 and T increased after spawning. The comprehensive study indicated that salinity had a certain effect on five hormones in the hemolymph of female E.sinensis during reproduction, five hormones didn’t change significantly in the process of mating, DHP, GTH and PG were involved during the spawning of E.sinensis.

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.