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A 56‐day feeding experiment was performed to investigate the effects of the dietary lipid level on the survival, growth performance, digestive enzyme activities and antioxidant capacity of Eriocheir sinensis reared under three salinities. Six feeds with graded levels of lipids (5%, 7%, 9%, 11%, 13% and 15%) were formulated by including fish oil as the main lipid source. Sixty crab individuals (initial weight: 0.21 ± 0.02 g) were assigned to each aquarium. In total, 18 aquariums were distributed under each salinity condition. Each feed was randomly allocated to three parallel tanks of crabs. The feeding experiment lasted for 56 days. Results showed that the survival rate of E. sinensis fed diets with 7%–15% lipids just showed a decreasing tendency as the salinity increased. The highest weight gain rate (WGR) was found in the treatment with 11%, 9% and 5% lipid at the salinity of 0.5‰, 2‰ and 6‰ respectively. At the salinity of 0.5‰, 2‰ and 6‰, the highest activities of antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase) were detected in the treatments with 11%, 13% and 7% lipid respectively. As the salinity increased, the protein and lipid contents showed an increasing trend, while the moisture content showed an opposite trend. At each salinity, arachidonic acid and docosahexaenoic acid increased, while saturated fatty acids and monounsaturated fatty acids decreased with the increase of dietary lipid level. These results indicated that increasing salinity resulted in decreased antioxidant enzyme activities and increased malondialdehyde content in the juvenile E. sinensis, especially when they were fed diets with relatively higher lipid level. Based on WGR, digestive enzyme activity and antioxidant capacity, the optimal lipid level was estimated to be 8.28–13%, 7.54–13% and 5–8.89% for juvenile E. sinensis reared at the salinity of 0.5‰, 2‰ and 6‰ respectively. [ABSTRACT FROM AUTHOR]

A 60‐day feeding experiment was performed to investigate the survival, growth, body composition, antioxidant capacity and related gene expression of Eriocheirsinensis which were fed diets with different lipid sources under three salinities. Five feeds were formulated with one of the candidate oils (fish oil, soybean oil, linseed oil, colza oil or palm oil) and were named FO, SO, LO, CO or PO respectively. Results showed that the survival rate (SR) of E. sinensis showed a decreasing tendency as the salinity increased. But SR was not significantly affected by dietary lipid sources at each salinity. Weight gain rate (WGR) were highest in the treatment of FO/PO at a salinity of 0.5‰, CO/FO/SO at a salinity of 2‰ and LO at a salinity of 6‰ respectively. At salinities of 0.5‰ and 2‰, the transcription of pro‐inflammatory and antioxidant genes in LO was significantly higher than that in FO or PO. While at a salinity of 6‰, the transcription of detected genes in FO was markedly increased compared to that in the vegetable oil treatments. At each salinity, the eicosapentaenoic acid (EPA) contents showed comparable values among different dietary treatments. However, the docosahexaenoic acid (DHA) contents in E. sinensis fed the diets with FO were still significantly higher than those with vegetable oils. These results showed that increasing salinity decreased the antioxidant capacity and therefore negatively affected the survival and growth rates of experimental animals. The beneficial effects of FO on survival and growth performance were eliminated by increasing the salinity to 6‰, which could be due to the increased lipid peroxidation and inflammatory response caused by salinity stress. It was concluded that at the salinity of 0.5‰ and 2‰, the recommended lipid sources were FO/PO and CO/FO/SO respectively. While at the salinity of 6‰, LO was the most ideal lipid source for juvenile E. sinensis. [ABSTRACT FROM AUTHOR]

A 60‐day feeding experiment was conducted to evaluate the survival, growth, antioxidant capacity and body composition of the juvenile Chinese mitten crab (Eriocheir sinensis) reared at three salinities (0.5‰, 2‰ and 6‰) in response to the different substitution levels (0%, 24%, 39%, 57% and 100%) of fish meal (FM) by soybean meal (SBM). The five diets were named as S0, S24, S39, S57 and S100 respectively. Results showed that survival rate (SR) was only significantly affected by the substitution level at the salinity of 0.5‰, with significantly higher SR observed in S39 (p < 0.05). At the salinity of 0.5‰ and 2‰, the significantly higher weight gain rate (WGR) was observed in S39 and S57 respectively (p < 0.05). At the salinity of 6‰, WGR was significantly improved by partial or complete substitution of FM by SBM. At each salinity, the highest GSH‐Px activity and lowest MDA content were observed in the treatments of S57, which were comparable to that fed S0. At the salinity of 6‰, the activities of SOD and CAT were significantly decreased in S100 than that in the other treatments (p < 0.05). The proline content significantly increased as the substitution level increased at the salinity of 2‰. At the salinity of 6‰, the contents of proline, glutamine, cysteine, methionine and lysine, first significantly increased and then decreased (p < 0.05), with the highest value observed in the treatment of S39 or S57. These results indicated that the optimal substitution level of FM by SBM was estimated to be 39% and 57% in the diets of E. sinensis at the salinity of 0.5‰ and 2‰ respectively. Although the FM can be completely replaced by SBM without negatively affecting the survival and growth performance at the salinity of 6‰, the antioxidant capacity was reduced to a large extent. [ABSTRACT FROM AUTHOR]

A 50‐day feeding experiment was conducted to investigate the effects of dietary protein level (26%, 34%, 43% and 52%) on the survival, growth performance, digestive enzyme activities, antioxidant capacity and body composition in the Chinese mitten crab (Eriocheir sinensis) reared at three salinities (0.5‰, 2‰ and 6‰). Survival rate (SR) showed a clearly decreasing tendency as the salinity elevated. The highest weight gain rate (WGR) was achieved in the treatment of 43% protein at the salinity of 0.5‰ and 2‰, and 26% protein at the salinity of 6‰ (p > 0.05). However, there was no significant interactive effect between dietary protein level and salinity on the SR and WGR of E. sinensis (p > 0.05). As salinity increased, the amylase activity and lipid deposition increased but the Na+/K+‐ATPase activity decreased. The MDA content of E. sinensis was increased at the salinity of 2‰ than the other two salinities by low or moderate dietary protein (26–43% dry diet), but was significantly decreased by high protein (52% dry diet). Correspondingly, the activities of GSH‐Px were increased at the relatively higher protein (43–52% dry diet). The significant interactive effect was only obtained between dietary protein level and salinity on the activities of CAT, GSH‐Px and MDA content of E. sinensis. Dietary protein level had a more obvious positive effects on the EAA deposition at the salinity of 2‰ and 6‰, with the highest contents of essential amino acids (EAAs) achieved by 43% dietary protein. In conclusion, the relatively higher protein could benefit the E. sinensis by inhibiting the lipid peroxidation and increasing the deposition of EAAs at the salinity of 2‰. The elevated activities of amylase could account for the low protein (26%) requirement for E. sinensis reared at the salinity of 6‰. [ABSTRACT FROM AUTHOR]