生物絮团技术对异育银鲫生长性能和抗性的影响

Effects of biofloc technology on growth performance and disease resistance of gibel carp, Carassius auratus gibelio

为研究生物絮团技术(Biofloc Technology,BFT)在沿海滩涂鱼类养殖中的应用效果,本实验以滩涂主要养殖种类——异育银鲫(Carassius auratus gibelio)为研究对象,按照BFT养殖模式(BFT组,不换水,只补存蒸发掉或取样部分的水分)和一般养殖模式(对照组,每日换水1次,每次换水1/4~1/3)分别饲养,测定各处理组异育银鲫的生长指标、消化酶活性和免疫相关酶活性,应用实时荧光定量PCR法定量分析热休克蛋白HSP70的相对表达,人工感染试验对比分析BFT养殖模式组和一般养殖模式组异育银鲫生长性能和抗性的变化。结果显示:(1)BFT组异育银鲫增重率、特定生长率和存活率均高于对照组(P<0.01),肥满度、脏体比和肝体比与对照组间无显著差异(P>0.05);(2)BFT组异育银鲫肠道中淀粉酶、脂肪酶和胃蛋白酶活性显著高于对照组(P<0.05),分别提高了53.10%、28.10%和17.99%;(3)BFT组异育银鲫体表黏液中超氧化物歧化酶活性、血清中总抗氧化能力和溶菌酶活性高于对照组(P<0.01);(4)BFT组脾、肾、肝和鳃中热休克蛋白HSP70的表达量分别上调了1.29倍、1.34倍、1.87倍和1.68倍;(5)嗜水气单胞菌(Aeromonas hydrophilia)人工感染试验证实,BFT组异育银鲫抗细菌感染能力显著增强。研究表明,BFT养殖模式适于异育银鲫养殖,可促进鱼体生长,增强其应激能力和抗病力。

Biofloc technology （BFT） is a zero-water exchange, environmentally friendly aquaculture system that is now widely used since it is proven to enhance the growth and immunity of farmed fish. Gibel carp Carassius auratus gibelio （also known as Prussian carp） is a major aquaculture species in China, especially around Yancheng in Jiangsu Province, and it is also grown in mudflats. Developing an effective aquaculture system for gibel carp is also helpful for exploring mudflats usage in fish aquaculture. However, sudden outbreaks of disease have become a great and common threat to carp-farming operations, as this causes huge economic losses. Since 2009, an epizootic with severe mortality rates caused by eyprinid herpes virus 2 （CyHV-2） has emerged among cultured gibel carp in China, especially in the northem part of Jiangsu Province. The disease develops fast, spreads widely to almost all main areas of gibel carp, and mortalities may reach 90%-100%. Thus, disease becomes a limiting factor for aquaculture, yet effective methods to prevent or control CyHV-2 are lacking. In order to discuss the practical usage of BFT in mudflat fish culture in terms of disease prevention, this study subjected the representative species （gibel carp） to the disease, using fish cultured in two different systems： in a BFT system without any water exchange, and in a common recirculating system with 1/4-1/3 water exchange daily （as control）, to analyze the effect of BFT on growth performance and disease resistance in this carp. Growth factors, digestive enzymes, and immune-related enzyme activities were detected by common methods using commercial kits; heat-shock protein 70 （HSP70） mRNA relative expression was analyzed with qRT-PCR; and disease resistance against bacterial infection was evaluated by challenge tests. The results demonstrated the following： （1）The rates of weight gain, specific growth, and survival of the gibel carp in the BFT group were significantly higher than occurred for fish in the control group （P〈0.01）; however, the condition factor and viserosomatic ration did not significantly differ between the two groups （P〉0.05）. （2）The activity of digestive enzymes （i.e., amylase, lipase and protease） in the BFT group was significantly enhanced （by 53.10%, 28.10% and 17.99%, respectively） in comparison with the control group （P〈0.05）. （3）The super oxide dismutase activity in skin mucus, total antioxidant capacity in liver, and ly- sozyme in serum were significantly induced in the BFT group （P〈0.01）. （4）HSP70 mRNA relative expression in the BFT group was up-regulated 1.29-, 1.34-, 1.87- and 1.68-fold in the spleen, kidney, liver and gill, respectively. （5）Disease resistance against bacterial infection was improved in the gibel carp eventually challenged by Aeromonas hydrophila. The cumulative mortalities of gibel carp cultured in the BFT system after experimental injection with bacterial concentrations of 4.2×10^7 CFU/mL, 4.2×10^6 CFU/mL and 4.2×10^5 CFU/mL, were 62.5%, 25%, and 0 within 7 days, respectively. These values were much higher than those detected among fish in the control system （i.e., 75%, 37.5% and 12.5%）. This study demonstrated that BFT can improve growth performance, digestive enzyme activity, and disease resistance of gibel carp, and that BFT could be successfully more often used in mudflat fish aquaculture. We suggest that future studies with gibel carp cultured in BFT systems should investigate the optimum concentrations of total suspended solids, prebiotics specialized for mudflat fishes, and relevant molecular immune mechanisms.