Progress in Fishery Sciences (Feb 2023)
Effects of Dietary Lipid and Lipase Levels on Growth Performance, Serum Biochemical Indices, and Liver Antioxidant Activity of Brachymystax lenok
Abstract
With the increasing demand for marine fish and cold-water predatory fish, to ensure its scale and industrialization in the process of breeding and to provide safe, high-quality, and healthy aquatic animal food for the society, the quality requirements of aquatic compound feed in the industry are increasing. Among the three nutrients, predatory fish have a poor ability to use sugar. Protein is the most expensive raw material, and the final product of its metabolism is ammonia, which can lead to the deterioration of water quality. Fat provides energy for fish growth, and essential fatty acids promotes the absorption of fat-soluble vitamins, and promotes protein deposition and utilization as a non-protein energy substance. Therefore, increasing the oil content in predatory fish feed and reducing the use of protein as energy can save feed protein and increase economic benefit. Different fish have different responses to nutrients and energy in feed. The fat metabolism of cultured fish has a certain species-specificity. It is generally believed that cold-water fish have a higher dietary fat requirement. The fat requirement of juvenile salmonids is 20%~30%, much higher than that of warm water fish. As a cold-water fish, Brachymystax lenok has successfully evolved key genotypic or phenotypic traits to adapt to growing at low temperatures, with fat requirements in the range of 17%~19%, slightly below the recommended fat requirements for regular Salmonidae fish.The high-fat feed has been widely used in carnivorous cold-water fish. As physiological conditions limit the demand and utilization capacity of fat, long-term intake of high-fat feed will easily cause fat metabolism disorder and meat quality decline during the breeding period, which seriously affects the health and quality of fish. Nutritional regulation of fat metabolism has become feasible means to reduce body fat deposition and improve meat quality. Therefore, it is particularly urgent to elucidate the fat metabolism mechanism and nutrition regulation of predatory fish. Lipase plays an essential role in lipid metabolism. As an enzyme with affinity at the oil-water interface, glycerol and fatty acids obtained after lipid hydrolysis can provide energy for the animal body and be utilized for its growth. Therefore, adding lipase in feed to regulate body fat nutrition has garnered considerable attention. Exogenous lipase has been well used in broilers and pigs to improve growth performance and physiological metabolism. It is also widely used in fish. However, it is rarely reported in the studies on cold water and freshwater fish nutrition. B. lenok is a rare and cold-water fish found in clear rivers and streams in China. The optimum temperature range for its growth is 18~20℃, and it has very high economic, edible, and research value.This study aims to, through adding different levels of lipase in different fat feed, use lipase in fat metabolism under the effect of high-fat feedstuff stress B. lenok to fat metabolism regulation, nutrition research on B. lenok growth performance, serum biochemical indices, and liver antioxidant effect, for lipase in B. lenok feeds for young fish provide a reference for the application. In this experiment, a 2×3 two-factor experimental design was used to prepare six experimental diets with two lipid levels (180 and 220 g/kg) and three lipase levels (0, 2500, and 5000 U/kg): C-0, C-2500, C-5000 and H-0, H-2500, H-5000. A total of 270 B. lenok with an initial body weight of (7.34±0.16) g were randomly divided into six groups with three replicates and 15 fish per replicate. Fish in each group were fed six different experimental diets for 63 days. The results show that different fat content and lipase level had extremely significant interaction on average body weight (P < 0.01) and significant interaction on weight gain rate and specific growth rate (P < 0.05). Both fat and lipase had an impact on the growth performance of the body. The body weight, weight gain rate, and specific growth rate of fish in the C-5000 group were the highest. Serum alanine aminotransferase (ALT) levels in H-0, H-2500, and H-5000 groups were lower than those in C-0, C-2500, and C-5000 groups, respectively. There were significant differences between H-0 and H-5000 groups and those in C-0 and C-5000 groups (P < 0.05). The low-density lipoprotein cholesterol (LDL-C) in H-0, H-2500, and H-5000 groups was higher than in C-0, C-2500, and C-5000 groups, respectively. There was a significant difference between H-0 and H-2500 groups, and the C-0 and C-2500 groups (P < 0.05). With the increase of lipase level, liver glutathione peroxidase (GPX) level increased. The GPX of the 220 g/kg group with the same lipase level was higher than that of the 180 g/kg group. In conclusion, the growth and antioxidant performance of juvenile B. lenok can be significantly improved at a lipid level of 183.7 g/kg, and the lipase level of 5000 U/kg.
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