Effects Of Fish Protein Hydrolystate On Growth, Metabolism, Flesh Quality, Immunity And Antioxidation In Large Yellow Croaker

Large yellow croaker (Pseudosciaena crocea) belongs to predatory fish species, and is one kind of economically important marine fish species in China. With high nutritive value and better flavor, it is popularly consumed by people. Due to excessive harvest, wild large yellow croaker has nearly been depleted. Since the success of artificial hatchery in the 1980s, its culturing has been developed rapidly. The purpose of the present study was to determine biochemical composition of large yellow croaker cultured in traditional sea-cages. Comparison of amino acid, fatty acid composition in muscle was conducted between this species fed different diets (raw fish and commercial feed). The effects of dietary fish protein hydrolysate on growth performance, metabolism, flesh quality, immunity performance were also evaluated. This dissertation was described in the following five sections.1 The analysis of biochemical composition in muscle from large yellow croaker cultured in traditional sea-cagesThe biochemical composition of fillets in large yellow croaker cultured in traditional sea-cages was determined. The comparison of amino acid and fatty acid composition was made between the fish fed with raw fish (RF) and commercial feed (CF). The analysis results showed that there were no significant differences in crude protein and ash content between two groups. Fish in CF group had lower level of crude fat content (P<0.05). Threonine, glutamic acid and alanine levels were significant higher, while glycine, methionine, leucine, phenylalanine, lysine, arginine and praline levels were significant lower in CF group (P<0.05). The percentages of total saturated fatty acids and monounsaturated fatty acids were significantly higher, while the corresponding total polyunsaturated fatty acids content was significantly lower in CF group (P<0.05). Among polyunsaturated fatty acids, n-3 PUFA and n-6 PUFA contents in RF group were higher. And large yellow croaker fed raw fish had the lower value of n-3/ n-6 ratio (P<0.05). 2 Effects of dietary FPH on growth performance and digestive enzyme activity in large yellow croakerThe study was conducted to investigate the effects of dietary supplementation with fish protein hydrolysate (FPH) on growth performance and digestive enzyme activity of large yellow croaker (Pseudosciaena crocea). Fish were fed 4 diets: basal diet only (control group, CG) or diets supplemented with FPH at doses of 5%, 10%, and 15% (treatment group, TG 1-3). The trial lasted for 10 weeks.Compared with the control group, total weight gain (TWG), relative weight gain (RWG) and specific growth rate (SCR) in TG2 and TG3 were significantly increased (P<0.05). Among all treatment groups, the results in TG2 were best: 101.9±11.89g, 62.41±7.62% and 0.86±0.08%, respectively. No significant differences were observed in the condition factor and visceral index of fish in four groups. Hepatosomatic indices of fish in TG2 and TG3 were significantly lower than CG (P<0.05).The protease activity of stomach, pylorus cecum, foregut and hindgut in all treatment groups were significantly higher than CG (P<0.05). Protease activity of stomach in TG2 and TG3 peaked, no significant difference was observed between two groups (P<0.05).There were no significant differences in protease activity of hepatopancreas among all groups (P<0.05). FPH had no significant effects on lipase and amylase activity of large yellow croaker.3 Effects of dietary FPH on serum biochemical indices in large yellow croakerThe results showed that serum total protein level in treatment groups were significantly higher (P<0.05), while urea nitrogen and total cholesterol levels were significantly lower than control group (P<0.05). No significant differences were found in glutamate-pyruvate transaminase, high density lipoprotein- cholesterol and magnesium levels among all groups. Serum calcium levels in TG2 and TG3 were significantly increased (P<0.05), triacylglycerol levels were significantly decreased (P<0.05). The differences between TG2 and TG3 were not significant.4 Effects of dietary FPH on flesh quality in large yellow croakerThe effects of dietary supplementation with FPH on body composition, IMP and volatile flavor components of large yellow croaker (Pseudosciaena crocea) were investigated. Moisture and crude protein content in treatment groups were significantly higher, while crude lipid content were significantly lower than control group. With the increasing levels of dietary FPH, essential amino acids and flavour amino acids contents in fillets of large yellow croaker increased significantly (P<0.05). The differences among treatment groups were not significant. Fish in all treatment groups contained lower SFA contents and higher MUFA, PUFA contents. Among PUFAs in treatment groups, EPA and DHA levels were significantly increased (P<0.05). The differences of SOD activity and MDA content among all groups were not significant. IMP content in fillets of large yellow croaker was significantly increased by supplementing FPH into basal diets (P<0.05).Volatile flavour compounds from muscle of large yellow croaker were extracted by microwave distillation and solid phase microextraction. The technique of gas chromatography-mass spectrometry was employed to analyze the components, and 54 compounds (alcohols, aldehydes, and ketones mostly) were identified. By comparing the results of all groups, the percentage profiles of components were not affected by dietary FPH levels.5 Effects of dietary FPH on immunity and antioxidation in large yellow croakerThe results showed that dietary FPH levels had no significant influence on KBI and SBI in large yellow croaker. Positive results were observed in immune parameters (lysozyme activity, serum complement, IgM). Lysozyme activity, complement C4 and IgM levels were significantly increased (P<0.05) in TG2 and TG3. Compared with CG, complement C3 level in TG1 were significantly increased (P<0.05), while no significant difference was shown in levels of lysozyme activity, complement C4 and IgM between two groups. The number of NBT-positive cells in peripheral blood among all groups were not significantly different (P>0.05).Hepatic SOD activities in treatment groups were all significantly higher than control group (P<0.05). The differences among three treatment groups were not significant. No significant differences were found in hepatic GPX and CAT activities among all groups. And the ratios of CAT/SOD in treatment groups were lower than control group.