Effects of Dietary Protein and Lipid Levels on Growth, Body Composition, Blood Biochemistry, Antioxidant Capacity and Ammonia Excretion of European Grayling (Thymallus Thymallus)

Background: This study evaluated growth, body composition, blood biochemistry, antioxidant capacity, innate immunity and ammonia excretion of European grayling (Thymallus thymallus) fed diets containing different protein and lipid contents. Six diets were produced to contain 30, 40 or 50% protein with 10 or 20% lipid and fed to triplicate groups (100 fish per replicate) of fish (25.2 ± 0.28 g) to visual satiety twice daily for 12 weeks. Results: Fish growth was enhanced (P ˂ 0.05) as protein increased from 30 to 40% and plateaued thereafter. Enhancing protein and lipid content of diet led to reduced feed intake and improved feed efficiency. Moreover, protein efficiency ratio increased at higher lipid level while lower values were recorded at higher protein levels. Increasing dietary lipid content led to the enhancement of viscerosomatic index and intraperitoneal fat ratio. An interaction of protein and lipid was found on whole-body lipid, and muscle lipid was responsive to dietary lipid level. Muscle ARA, EPA and Ʃn-6 LC-PUFA contents enhanced by increasing dietary protein level. Moreover, increasing fat content of diet led to enhanced muscle linoleic acid, linolenic acid, ƩMUFA, Ʃn-6, DHA/EPA and n-6/n-3. However, EPA, DHA, Ʃn-6 LC-PUFA, Ʃn-3, Ʃn-3 LC-PUFA and EPA/ARA decreased at higher dietary lipid level. Serum triglyceride (TG) concentration and lactate dehydrogenase (LDH) activity decreased as dietary protein level increased while an opposite effect was observed for cholesterol (CHO) concentration. Increasing fat content of diet led to enhanced serum TG, CHO and glucose concentrations and reduced alanine aminotransferase, aspartate amino transferase and LDH activities. Serum malondialdehyde concentration was enhanced by increasing both dietary protein and lipid contents. Furthermore, serum myeloperoxidase activity was enhanced at higher dietary lipid level. Water total ammonium nitrogen (TAN) concentration was measured after 5 and 24 h of last feeding, and the results indicated the reduction of ammonia excretion as dietary lipid content increased. Conclusions: These findings suggest that 40% dietary protein can support optimal growth of juvenile European grayling and increasing lipid content from 10 to 20% can improve feed utilization and reduce ammonia excretion to the rearing water.

Effects of dietary lipid level on growth, fatty acid profiles, antioxidant capacity and expression of genes involved in lipid metabolism in juvenile swimming crab, Portunus trituberculatus

The regulation of lipogenesis and lipolysis mechanisms related to consumption of lipid has not been studied in swimming crab. The aims of the present study were to evaluate the effects of dietary lipid levels on growth, enzymes activities and expression of genes of lipid metabolism in hepatopancreas of juvenile swimming crab. Three isonitrogenous diets were formulated to contain crude lipid levels at 5·8, 9·9 and 15·1 %. Crabs fed the diet containing 15·1 % lipid had significantly lower growth performance and feed utilisation than those fed the 5·8 and 9·9 % lipid diets. Crabs fed 5·8 % lipid had lower malondialdehyde concentrations in the haemolymph and hepatopancreas than those fed the other diets. Highest glutathione peroxidase in haemolymph and superoxide dismutase in hepatopancreas were observed in crabs fed 5·8 % lipid. The lowest fatty acid synthase and glucose 6-phosphate dehydrogenase activities in hepatopancreas were observed in crabs fed 15·1 % lipid, whereas crabs fed 5·8 % lipid had lower carnitine palmitoyltransferase-1 activity than those fed the other diets. Crabs fed 15·1 % lipid showed lower hepatopancreas expression of genes involved in long-chain-PUFA biosynthesis, lipoprotein clearance, fatty acid uptake, fatty acid oxidation, lipid anabolism and lipid catabolism than those fed the other diets, whereas expression of some genes of lipoprotein assembly and fatty acid oxidation was up-regulated compared with crabs fed 5·8 % lipid. Overall, high dietary lipid level can inhibit growth, reduce antioxidant enzyme activities and influence lipid metabolic pathways to regulate lipid deposition in crab.

Integrated metabolomic and transcriptomic analyses suggest that high dietary lipid levels facilitate ovary development through the enhanced arachidonic acid metabolism, cholesterol biosynthesis and steroid hormone synthesis in Chinese sturgeon (Acipenser sinensis)

Chinese sturgeon (Acipenser sinensis) is an endangered species, listed as a grade I protected animal in China. The females rarely successfully develop their gonads from stage II to III in captivity, which handicaps the propagation of cultured Chinese sturgeon. The present study aimed to understand the effects of dietary lipid level on the ovarian development and the related regulation mechanism in female Chinese sturgeon. A 24-month feeding trial was conducted with 10-year-old Chinese sturgeons with ovaries at the developmental stage II, with three experimental diets containing 10, 14 and 18 % lipids. Ovary, muscle and serum samples were collected at four time points (6, 12, 18 and 24 months) for further analyses. Serum metabolomics and ovary transcriptomics analyses were conducted at 18 months. Results showed that only the 18 % lipid diet promoted ovary development to stage IV. Oocytes at stage II in this group also exhibited higher diameter and more lipid droplets. Serum TAG content in the 18 % group was significantly higher than in 10 and 14 % groups (both at 12 and 18 months). Oestradiol content in the 14 % group was significantly higher than in 10 and 18 % groups, except at 24 months. Metabolomic and transcriptomic results indirectly indicated that 14 % of dietary lipids benefited steroid hormone synthesis, while 18 % lipid facilitated arachidonic acid metabolism, cholesterol biosynthesis and vitellogenesis, although serum cholesterol content did not vary with dietary lipid level. In conclusion, 18 % dietary lipid is the optimal level for improving gonad development of female Chinese sturgeon.