ANALYSIS ON THE COMPOSITION OF AMINO ACID AND FATTY ACID AND THEIR CHANGES DURING EARLY GROWTH STAGE OF SEBASTES SCHLEGELII

The black rockfish (Sebastes schlegelii) has been an important economic marine fish species of deepwater cage farming, enhancement releasing and fishing in the northern coast of China. Its reproduction is ovoviviparous, during which the embryo is produced in female fish and usually grow to free fish around May. There is no report on the nutritional requirements and metabolic characteristics of the early development of S. schlegelii. In order to investigate the compositions of amino acids and fatty acids as well as their changes for S. schlegelii in different developmental stages, related analysis at different stages including fertilized eggs (FE), embryo stage (ES), primiparous larvae (PL₁), pre-larva (PL₂), post-larva (PL₃) and juvenile (J) were conducted by biochemical analysis methods. The S. schlegelii was sampled at the breeding demonstration base of Shandong Marine Resource and Environment Research Institute, Yantai, Shandong Province from April to July in 2016. The results showed that the total amino acid content decreased significantly from FE to PL₁, and then increased significantly during prophase PL₃, and finally had another significant decrease in the late stage of J (P<0.05). The total amount of free amino acid during FE was the lowest among the six stages (12.77 mg/g), which then significantly increased from FE to PL₁ (P<0.05), and reached to the highest level of 92.19 mg/g, and after that it diminished first, then rose, and decreased again (P<0.05). The content of free essential amino acids was significantly higher than that of free nonessential amino acids at each developmental stage. The percentage of free amino acids at each stage was 2.37%—19.66%. Twenty-nine fatty acids were detected in S. schlegelii, including 9 saturated fatty acids (SFA), 10 single unsaturated fatty acids (MUFA) and 11 poly unsaturated fatty acids (PUFA). The major fatty acids in fertilized eggs were C_22:6n-3 (DHA), C_18:ln-9c, C_16:0 and C_20:5n-3. At the embryonic period, the order of utilization rate of fatty acid was SFA, MUFA, n-6PUFA and n-3PUFA. Meanwhile, C_18:3n-3, C_18:0, C_16:1n-7 and C_20:5n-3 were main sources of energy metabolism. n-3PUFA was preserved at priority, and especially the actual utilization ratio of C_{22: 6n-3} (DHA) is the lowest (9.71%) and the highest practical utilization amount was C_16:0 (10.94 mg/g). The order of utilization rate of fatty acid at the endogenous feeding stage was MUFA, n-6PUFA, SFA and n-3PUFA. C_16:1n-7, C_18:0, C_20:4n-6(ARA) and C_18:1n-9c were main sources of energy metabolism, and the highest practical utilization amount was DHA (18.23 mg/g). Compared to EPA and ARA, DHA was preferentially utilized from primiparous larvae to post-larva. While ARA was preferentially utilized during post-larva and juvenile other than EPA and DHA. Therefore, the change trends were completely different between total amino acid and free amino acid content in vivo developmental stages. The practical utilized amount and utilization ratio were different in embryo stage and endogenous feeding stage. Polyunsaturated fatty acid DHA was preferentially utilized in larval stage, while ARA was preferentially utilized in juvenile. It was recommended to enhance biological bait enriched with DHA in larval breeding of S. schlegelii and add ARA on pellet feed in juvenile. This method can prevent fingerlings of nutrition inadequacy and guarantee survival rate.