鲈鱼利用鱼粉和植物蛋白源的选择性摄食关键原因及调控机制的研究

Voluntary anorexia is the main factor for limiting utlization of plant protein in carnivious fish speices.Similar to the mammals, the regulation of appetite and body weight is a complex phenomenon involving elaborate interactions between the brain and peripheral signals. However, the key factor and mechanism of feeding preference and feed intake control are not clear. Especially the research on the mechanism of feeding adaptation and compensation are totally unknow.The activities of Ghrelin/leptin-NPY/POMC and mTOR-NPY system are important signal pathway of central and peripheral control of food intake. We had found that, partially replacement of fishmeal by plant protein induced anorexigenic phenomenon (anorectic). Inhibited feed intake is the main reason for poor growth performance. However, conditional feeding adaptation and compensation could be observed after a longer term feeding trial. A long-term growth trial will be conducted to study the growth performance, feeding behaviour and conresponding feeding controlling mechanism of anorectic-adaptation-compensation behaviour fed high plant protein diets on the carnivorous species, Japanese seabass by animal nutrition and molecular methodologies. After than, we will limiting fed or starv the fish to determine the mechanism of voluntary and passive anorexia on Japanese seabass. The genes related to the Grelin/leptin-NPY/POMC and mTOR-NPY signaling pathway of the Japanese seabass will be cloned. Total RNA will be extracted from related tissues and expressed by real-time PCR. The results of studies will provide scientific basis for appetite, feeding behavior, adaptation and body weight regulation mechanism of Japanese seabass.

对植物蛋白饲料的厌食现象是肉食性鱼类对鱼粉依赖性较强的主要原因。和哺乳动物相同，鱼类摄食行为受中枢和外周调控，主要调控因子的功能也基本一致，但鱼类对不同蛋白源饲料主动性选择和回避，对植物蛋白源的适应和补偿性摄食现象的关键原因及其调控机制尚不明确。本项目拟以植物蛋白替代鱼粉为主线，通过观察鲈鱼对鱼粉或高植物蛋白饲料的摄食和生长反应，研究人为限食和恢复投喂时摄食行为和生长性能的变化，克隆Ghrelin/Leptin-NPY/AGRP和mTOR-NPY食欲调控系统相关基因序列全长，检测中枢和外周组织中食欲调控相关基因的mRNA水平以及循环系统中相关神经肽和激素含量的变化，从表观和分子机理两个层次系统研究鲈鱼对鱼粉和植物蛋白源选择性摄食的关键原因及其对植物蛋白饲料从摄食抑制到适应再到补偿的调控机制，以及主动和被动摄食抑制之间调控模式的差异，为鲈鱼摄食生理的深入研究与合理使用饲料蛋白源提供科学依据。

鱼粉替代问题已经成为限制水产养殖产业的首要问题。植物蛋白替代鱼粉后，对植物蛋白饲料的厌食现象是肉食性鱼类对鱼粉依赖性较强的主要原因。同哺乳动物一样，鱼类摄食行为受外周和中枢摄食信号系统调控，但鱼类对植物蛋白源饲料的主动性选择和回避的关键原因及调控机制尚不明确。本论文以花鲈为研究对象，探究植物蛋白源替代鱼粉对花鲈生长性能和摄食调控机制的影响。以混合植物蛋白替代50%、100%低温干燥鱼粉，设计等氮等能的三种饲料，分别命名为FM、PPB50、PPB100，养殖周期为12周。分别在3d、2w、4w和12w餐后3h、6h、24h进行血浆和胃、下丘脑组织样品的采集。之后进行3w禁食和3w恢复摄食试验。.结果表明: 与鱼粉组相比，PPB100在短期内引起花鲈明显的厌食现象，且4周内PPB100组摄食率（FR）显著低于FM组；5-8周，花鲈已经适应植物蛋白，PPB100组FR显著高于FM组，但增重率（WG）仍低于FM组；9-12周，PPB100组持续保持旺盛的食欲，此阶段其FR和WG均显著高于FM组。即花鲈摄食完全植物蛋白饲料后，会出现抑制摄食到适应再到补偿摄食的行为。.空腹时，PPB组胃中ghrelin mRNA表达增加而leptin表达降低显示机体处于饥饿状态，但下丘脑mTOR蛋白磷酸化水平上调，进一步抑制下游靶蛋白S6K1的蛋白磷酸化，从而下调促食欲肽AgRP和上调抑制食欲因子POMC，由此可见中枢摄食调控系统对外周饥饿状态缺乏有效响应，是导致花鲈厌食的主要原因。4周后花鲈下丘脑促食欲肽AgRP mRNA表达水平出现反转，PPB组显著高于FM组，表明摄食植物蛋白饲料的花鲈此阶段处于积极索食状态，已经完全适应植物蛋白饲料。12周餐后24h，PPB组血浆ghrelin含量显著低于FM组，表明PPB组食欲更强，中枢神经系统抑食因子POMC的显著下调是此阶段产生补偿摄食的主要原因。人为禁食和恢复摄食试验结果表明植物蛋白饲料替代鱼粉引起的花鲈主动选择性摄食抑制与人为禁食处理导致的被动摄食抑制存在不同的调控机制。花鲈对植物蛋白源饲料存在适应能力，ghrelin/leptin-mTOR-S6K1-AgRP/POMC摄食信号通路能够有效的调控肉食性鱼类摄食植物蛋白后由厌食到适应再到补偿生长的摄食行为，对耐高植物蛋白养殖鱼类基因靶向育种，有效提高肉食性鱼类利用植物蛋白能力具有重要意义。