许氏平鲉幼鱼对饲料中维生素D3需求量的研究

Dietary vitamin D3 requirement of juvenile rockfish (Sebastes schlegelii)

关键词:  许氏平鲉  维生素D3  生长  免疫  需求量

Key words:  Rockfish (Sebastes schlegelii)  Vitamin D3  Growth  Immunity  Requirement

摘要:

本实验旨在研究维生素D3对许氏平鲉(Sebastes schlegelii)幼鱼生长、体组成及机体免疫能力的影响，以确定其对维生素D3的最适需求量。配制维生素D3含量分别为707、1254、1740、2513、4519和8671 IU/kg的6种等氮等脂饲料，饲养初始体质量为(20.95±0.05) g的许氏平鲉幼鱼，8周后进行哈维氏弧菌(Vibrio harveyi)攻毒48 h。研究表明，随着维生素D3含量的增加，许氏平鲉幼鱼增重率(WGR)和特定生长率(SGR)均先上升后下降，脏体比(VSI)和肝体比(HSI)显著下降，707 IU/kg组显著高于其他组(P<0.05)；全鱼粗脂肪和肌肉粗脂肪随维生素D3含量增加呈增加的趋势，在4519 IU/kg组有最大值并显著高于对照组(P<0.05)，脊椎骨粗灰分和钙含量显著增加；血清总抗氧化能力(T-AOC)、超氧化物歧化酶(SOD)活力和补体3 (C3)含量均先升高后降低，均在2513 IU/kg组有最大值，谷丙转氨酶(ALT)、谷草转氨酶(AST)活力和丙二醛(MDA)含量均先降低后升高，总胆固醇(T-CHO)、甘油三酯(TG)和钙离子含量(Ca2+)呈增加的趋势，磷(Pi)和补体4 (C4)含量不受维生素D3含量的影响(P>0.05)。攻毒后，T-AOC及MDA、C3和C4含量显著增高，肝脏和头肾HSP70、MYD88、IRAK4、TRAF6和TLR2基因表达显著升高(P<0.05)。以WGR为评价指标，经折线回归分析表明，体质量为(20.95±0.05) g的许氏平鲉幼鱼维生素D3的需求量为2 223.45 IU/kg饲料。

Abstract:

Rockfish (Sebastes schlegelii) is a near-shore, carnivorous coldwater fish, primarily distributed in the East China Sea, Korean peninsula, Japan, and the Sea of Okhotsk. Owing to its delicious meat, strong disease resistance, rapid growth, and other characteristics, it has become one of the main cultured fish in deep water cages in northern China. A high-quality and efficient formula diet for rockfish has not been developed because of nutrient requirement deficiencies. As vitamin D3 is the most important form of vitamin D and only exists in animals, cultured fish can only obtain vitamin D3 from their diet. Vitamin D3 can maintain the mineral homeostasis in fish, participate in the endocrine system, and affect the proliferation and apoptosis of immune cells. As such, this experiment was conducted to investigate the effects of dietary vitamin D3 on growth performance, body composition, and immune function of juvenile rockfish and determine the optimum dietary vitamin D3 requirement. Six kinds of isonitrogenous and isolipidemic diets with 707, 1254, 1740, 2513, 4519, and 8671 IU/kg of vitamin D3 were prepared by adding 0, 500, 1000, 2000, 4000, and 8000 IU/kg of vitamin D3 into the basic diet. Each diet was randomly assigned to triplicate groups of juveniles with initial bodyweights of (20.95±0.05) g for eight weeks. The fish were challenged with Vibrio harveyi for 48 hours after feeding. Results showed that, with the increase of vitamin D3 contents, both the weight gain rate (WGR) and specific growth rate first increased and then decreased, reaching a maximum value in the 2513 IU/kg group, which was significantly higher than that in the 707 IU/kg group. The feed conversion rate first decreased and then increased and was significantly lower in the 2513 IU/kg group than other groups. Both viscerosomtic index and hepatosomatic index decreased significantly and were significantly higher in the 707 IU/kg group than in other groups. There were no significant differences in the condition factor and survival rate among all groups. The crude fat of whole fish and muscle showed an increasing trend, reaching a maximum value in the 4519 IU/kg group, which was significantly higher than 707 IU/kg group. The crude muscle protein first decreased and then increased; the 8671 IU/kg group was significantly higher than the 1740 IU/kg and 2513 IU/kg groups. The moisture, crude protein, and crude ash of whole fish, as well as the muscle moisture and crude ash, had no significant differences in concentration among all groups. The spine crude ash showed an increasing trend; the 1740~8671 IU/kg groups had significantly higher contents than the 707 IU/kg group. The calcium contents increased with the increase of dietary vitamin D3 levels. Total antioxidant capacity (T-AOC) and superoxide dismutase activities first increased and then decreased, reaching a maximum in the 2513 IU/kg group. The malondialdehyde (MDA) contents first decreased and then increased; the 2513 IU/kg group had significantly lower content than the 707 IU/kg group. Complement 3 (C3) contents first increased and then decreased; the 707 IU/kg group had significantly lower content than the other groups. Alanine aminotransferase and aspartate aminotransferase first decreased and then increased, reaching minimum values in the 2513 IU/kg group. The highest cholesterol and triglyceride values were observed in the 4519 IU/kg group. The calcium (Ca2+) contents first increased with the increase of dietary vitamin D3 levels, with the 707 IU/kg group showing significantly lower content than other groups. The phosphorus and complement 4 (C4) contents were not affected by dietary vitamin D3. After the challenge, T-AOC, MDA, C3, and C4 were significantly elevated; T-AOC, C3, and C4 in the serum had maximum values in the 2513 IU/kg group, and MDA reached its minimum value in the 2513 IU/kg group. With the increase of dietary vitamin D3 content, HSP70, MYD88, IRAK4, TRAF6, and TLR2 in the liver, and head kidney increased first and then decreased before and after the challenge. Gene expression was significantly elevated after the challenge. Taking WGR as the evaluation index, a broken line regression analysis showed that the optimum dietary vitamin D3 requirement was 2 223.45 IU/kg diet for juvenile rockfish S. schlegelii with the body weight of (20.95±0.05) g.