许氏平鲉发育早期的氨基酸与脂肪酸组成及变化

为了研究许氏平鲉(Sebastes schlegelii)雌鱼体内受精后仔鱼开口前和仔鱼开口后两个阶段氨基酸和脂肪酸的组成变化规律, 采用生化常规方法定量测定并分析了许氏平鲉发育早期的受精卵(FE)、胚胎期(ES)、初产仔鱼(PL₁)、前仔鱼期(PL₂)、后仔鱼期(PL₃)和稚鱼期(J)6个阶段的氨基酸和脂肪酸组成特点及含量变动。结果表明: 总氨基酸含量从FE至PL₁显著下降, 至PL₃显著上升, 至J又显著下降(P<0.05); 游离氨基酸含量以FE最低(12.77 mg/g), 从FE到PL₁显著上升(P<0.05), 并在PL₁含量达到最高值(92.19 mg/g), PL₁发育到J呈现先下降后上升再下降的变化趋势(P<0.05), 游离氨基酸与总氨基酸的比值范围在2.37%—19.66%。在各发育阶段干样中检出碳链长度在C₁₄-C₂₄的29种脂肪酸, 分别为9种饱和脂肪酸(SFA)、9种单不饱和脂肪酸(MUFA)和11种多不饱和脂肪酸为(PUFA), 受精卵中主要脂肪酸依次为C_22:6n-3(DHA)、C_18:ln-9c、C_16:0和C_20:5n-3(EPA)。胚胎期(FE-ES)的脂肪酸利用率顺序为SFA、MUFA、n-6PUFA、n-3PUFA, 主要以C_18:3n-3、C_18:0、C_16:1n-7及C_20:5n-3(EPA)作为胚胎期的能量来源, C_22:6n-3(DHA)的实际利用率最低(9.71%), 被优先保存下来, C_16:0的实际利用量最高(10.94mg/g); 仔鱼内源营养阶段(ES-PL₁)脂肪酸利用率顺序为MUFA、n-6PUFA、SFA、n-3PUFA, 主要以C_16:1n-7、C_18:0、C_20:4n-6(ARA)及C_18:1n-9c作为开口前仔鱼的主要能量来源, 其中仔鱼对DHA实际利用量最高(18.23 mg/g)。PL₁-PL₃阶段DHA相对于EPA和ARA被选择性利用; PL₃至J阶段ARA相对于EPA和DHA被选择性利用。研究表明: 许氏平鲉仔鱼开口前阶段总氨基酸含量与游离氨基酸含量的变化趋势截然相反, 胚胎期与仔鱼内源营养阶段脂肪酸利用率和利用量均有所不同, 仔鱼期DHA优先被利用, 过渡至稚鱼期ARA优先被利用。建议在仔鱼开口后添加富含DHA生物性饵料, 仔鱼过渡到稚鱼期在配合饵料中添加ARA营养物质, 防止苗种营养不足, 保证成活率。

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.