Effects of Dietary Lipid and Lipase Levels on Growth Performance, Serum Biochemical Indices, and Liver Antioxidant Activity of Brachymystax lenok

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 met