混合微藻替代鱼油对大菱鲆幼鱼生长性能、体组成及肠道部分生化指标的影响

本实验以大菱鲆(Scophthalmus maximus)幼鱼[(39.69±0.25) g]为研究对象，探究由裂壶藻(Schizochytrium sp.)和拟微绿球藻(Nannochloropsis sp.)组成的混合微藻替代鱼油对幼鱼生长性能、体组成、肠道消化水平及抗氧化能力的影响，以确定混合微藻替代鱼油的适宜比例。通过在基础饲料中添加不同比例的混合微藻，分别替代0、25%、50%和100%的鱼油，制成4组等氮等脂的实验饲料(分别命名为D1、D2、D3和D4)，每组饲料设3个重复，实验周期为12周。结果显示，随替代比例的提高，大菱鲆幼鱼的增重率(WGR)和饲料效率(FE)呈下降趋势，D1、D2和D3组的特定生长率(SGR)和FE无显著性差异，但均显著高于D4组(P<0.05)；肝体比(HSI)在D1组达到最大值，且显著高于其他各组(P<0.05)；存活率(SR)和肥满度(CF)在各组之间无显著差异(P>0.05)。随着混合微藻替代鱼油比例的升高，全鱼和肌肉粗脂肪含量呈先升高后降低的变化趋势，且D4组显著低于D1组(P<0.05)；大菱鲆幼鱼鱼体中C20:4n-6和n-6 PUFA含量显著升高，在D4组均达到最大值，且显著高于对照组(P<0.05)。而EPA、DHA和n-3 PUFA含量随之显著下降，对照组(D1)含量显著高于其他各组(P<0.05)；肌肉中C20:4n-6和DHA含量在不同实验组间无显著性差异(P>0.05)，EPA和n-3 PUFA含量呈显著降低趋势(P<0.05)。肠道脂肪酶活力在D3组达到最大值，显著高于对照组(P<0.05)，肠道胰蛋白酶活力也是在D3组最高，但与对照组无显著性差异(P>0.05)。与D1组相比，D3组肠道中酸性磷酸酶(ACP)、碱性磷酸酶(AKP)、溶菌酶(LZM)活力和补体C3含量均显著升高(P<0.05)。肠道中超氧化物歧化酶(SOD)、总抗氧化能力(T-AOC)和过氧化氢酶(CAT)活力随替代比例的提高呈先升高后降低的趋势，均在D3组达到最大值，显著高于D1组(P<0.05)，而肠道中丙二醛(MDA)含量在不同实验组间并未表现出显著性差异(P>0.05)。综上所述，混合微藻替代50%的鱼油并不会对大菱鲆幼鱼的生长性能产生负面影响，同时可以提高肠道的消化性能、抗氧化能力和非特异性免疫能力。

Effects of fish oil replacement by mixed microalgae on growth performance, body chemical composition and intestinal tract biochemical indices of juvenile turbot (Scophthalmus maximus)

A 12-week feeding experiment was conducted to evaluate the effects of fish oil replacement by mixed microalgae on growth performance, body composition, digestive enzyme activities, and antioxidant indices in the intestinal tract of juvenile turbot (Scophthalmus maximus) [mean initial weight (39.69±0.25) g]. Four isonitrogenous and isoenergetic diets were formulated with graded contents of dietary fish oil replacement by mixed microalgae, 0, 25%, 50%, and 100%, designated D1, D2, D3, and D4, respectively. The results showed that weight growth rate (WGR) and feed efficiency (FE) decreased with an increasing replacement ratio; no significant differences were found between D1, D2, and D3 groups (P>0.05), but all three had significantly higher values than the D4 group (P<0.05). The D1 group showed the highest value of the hepatosomatic index (HSI), which was significantly higher than that in other groups (P<0.05). With an increasing replacement ratio, the body and muscle crude lipid contents increased at first, and then decreased, being significantly higher in the D4 group than in the D1 group (P<0.05). The C20:4n-6 and n-6 PUFA in the whole fish body reached their peaks in the D4 group (P<0.05), with significantly higher values than those in the D1 group (P<0.05). However, EPA, DHA, and n-3 PUFA significantly decreased in D4 (P<0.05). The activities of lipase and trypsin in the intestinal tract reached their peaks in the D3 group. The activities of superoxide dismutase (SOD), total antioxidant capacity (T-AOC), and catalase (CAT) in the intestinal tract of the D3 group were significantly higher than those in the D1 group (P<0.05). Additionally, the activities of acid phosphatase (ACP), alkaline phosphatase (AKP) and lysozyme (LZM), as well as the complement component 3 (C3) contents in the intestinal tract, showed the same tendency as SOD. The malondialdehyde (MDA) contents in the intestinal tract were not significantly different across the groups (P>0.05). These results indicate that 50% fish oil replacement by mixed microalgae does not influence the growth performance of juvenile turbot, and may increase the digestive enzyme activities and antioxidant ability in the intestinal tract.