A 60‐day feeding experiment was performed to investigate the survival, growth, body composition, antioxidant capacity and related gene expression of Eriocheir sinensis 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.

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.

A 60 d feeding experiment was conducted to investigate the effects of oxidized fish oil (OF) on survival, growth, immune and antioxidant capacity, inflammation-related gene expression, and intestinal microbiota of juvenile sea urchin (Strongylocentrotus intermedius). Six feeds were formulated by including equal amounts of fish oil with different oxidation levels (0, 50, 100, 150, 200, and 300 meq/kg). The feed OF0 and fresh kelp (Laminaria japonica) were used as the control groups. Results showed that the weight gain rate (WGR) of sea urchins significantly decreased as the oxidation level increased. When the oxidation level of fish oil was equal to or above 150 meq/kg, the WGR of sea urchins was significantly lower than those fed the control diets. The activities of digestive enzymes (pepsin and amylase), immune enzymes (alkaline phosphatase and acid phosphatase), and antioxidant enzymes (superoxide dismutase, catalase, and glutathione S-transferase) first decreased significantly as the oxidation level increased to 150 or 200 meq/kg and then bounced to values comparable to or even higher than those in the control feed group, while the transcription of immune, antioxidation, and inflammation-related genes was upregulated by the increasing oxidation level of fish oil. Oxidized fish oil decreased the intestinal microbial diversity and the relative abundance of Firmicutes. Vibrio was the dominant genus of microbiota in the intestine of sea urchins fed almost all formulated feeds (except for OF150), with its abundance above 20%. Comparably, the abundance of Vibrio in the intestine of sea urchins fed fresh kelp was only 2.32%. These results showed that oxidized fish oil had negative effects on the growth, immune response and antioxidant capacity, and bacterial diversity of juvenile S. intermedius. The abnormal increase of antioxidant enzyme activities and malondialdehyde contents at relatively higher oxidation level (>150 meq/kg) could be due to the oxidative stress occurrence inside the body of sea urchins. Sea urchins fed formulated feeds host more Vibrio than those fed fresh kelp, and this could be a potential incidence of disease occurrence.

This study was carried out to investigate the effects of five formulated feeds with different lipid sources (colza oil (CO), fish oil (FO), linseed oil (LO), soybean oil (SO), or palm oil (PO)) and kelp (Laminaria japonica) on the growth, reproductive performance of broodstock, and early larvae quality of sea urchin (Strongylocentrotus intermedius). The experimental diets were randomly allocated to a total of 48 (eight urchins per experimental group) individually cultured S. intermedius(initial weight 90.51 ± 0.82g) and the feeding period lasted for 12 weeks. The results showed that the weight gain rate of female sea urchins fed kelp was significantly higher than those fed formulated feeds while the gonadosomatic index of spawned female sea urchins fed kelp was significantly lower than those fed formulated feeds.S. intermedius broodstock fed FO showed the largest egg diameter and fecundity, which could be due to the abundant n-3 LC-PUFA deposited in the gonads of this group. Sea urchins fed SO showed the lowest fecundity and hatching rate, and the highest inflammation level. Sea urchins fed CO showed the highest content of oleic acid in the gonads and eggs, but the lowest fertilization rate. The highest hatching rate was observed in the kelp treatment, which was comparable to that in the LO and PO but was significantly higher than that in CO, FO, and SO. Before mouth opening, all prismatic larvae showed no significant differences in survival during the first 2 days post hatchery (DPH). At the 3 DPH, the survival of S. intermedius larvae was highest in the FO group, followed by those in the PO group, with the lowest survival observed in the kelp group. Thus, FO was accepted as the most ideal lipid source based on growth, reproductive performance, and early larval quality. These results could contribute to adopting an efficient feeding strategy to promote the reproductive performance and offspring quality by choosing the optimal lipid source for S. intermedius broodstock.