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We aimed to investigate the effect of xylooligosaccharides (XOS) on the growth performances and lipid metabolism of common carp fed high‐fat diets. 192 fish were randomly distributed into 24 tanks into six groups (four replicates) and were fed with control diet, high‐fat diet (HFD) and HFD supplemented with 5, 10, 20 and 30 g/kgXOS respectively for 8 weeks. Fish fed HFD supplemented with 10 g/kg XOS obtained higher final body weight, weight gain, specific growth rate and protein efficiency ratio compared to those fed control diet and HFD, while feed conversion ratio showed the opposite trend. Fish fed HFD obtained higher hepatosomatic index, abdominal fat, energy intake compared to other groups, whereas the opposite was true for nitrogen retention. High plasma levels of cholesterol, triglycerides, low‐density lipoprotein and low high‐density lipoprotein were observed in fish fed HFD; opposite was true for fish fed HFD supplemented with 10–20 g/kg XOS. The transcription of lipoprotein lipase was up‐regulated, whereas that of carnitine palmitoyltransferase I, peroxisome proliferator‐activated receptors alpha, acyl‐CoA oxidase and CD36 were down‐regulated in fish fed HFD. Opposite trend was observed in fish fed HFD supplemented with 10–20 g/kg XOS as well as the control group. In conclusion, XOS inclusion can benefit the growth performance and lipid metabolism of common carp fed HFD.

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This research investigated the effects of dietary cholesterol (CHO) on growth, molting performance, CHO deposition, and lipid metabolism of Chinese mitten crab (Eriocheir sinensis). Six diets were formulated to contain 0% (control), 0.1%, 0.2%, 0.4%, 0.8%, and 1.6% CHO and were administered to E. sinensis 43.35 ± 0.05   g , for 16 weeks. From our results, crabs fed with 0.2% and 0.4% CHO diet, the final body weight (FBW), and weight gain ratio (WGR) increased significantly and the feed conversion ratio (FCR) decreased significantly compared with that of the control group. Furthermore, the molting performance of E. sinensis was significantly improved in crabs fed 0.2% CHO. Meanwhile, 0.2% CHO tends to upregulate molt-promoting genes and downregulate the expression of molt-inhibiting genes. It indicated that CHO might improve the molting performance of crabs by regulating ecdysteroid signal pathway transduction. In addition, dietary CHO can significantly increase the content of CHO in the hepatopancreas, muscle, and hemolymph. Moreover, dietary CHO increases the content of triglyceride (TG) in the hepatopancreas and hemolymph. The gene-related lipid metabolism shows that CHO may increase the lipid content by promoting lipid synthesis and inhibiting lipolysis. According to the results of this study, the dietary CHO requirement of E. sinensis is 0.27% for growth requirement and 0.45% for tissue CHO deposition based on the broken-line model.