基于响应曲面法研究亚硝酸盐与养殖密度对吉富罗非鱼幼鱼生长与肝脏抗氧化力的影响

采用中心复合实验设计(CCD)和响应曲面方法(RSM),在实验室条件下探讨了亚硝酸盐(0.02—2.8mg/L)和养殖密度(1—5尾/10L)对吉富罗非鱼幼鱼生长和肝脏抗氧化指标(MDA含量,SOD与CAT活力)的联合影响。整个实验周期持续35d。结果显示,本实验条件下,亚硝酸盐和密度的一次效应和密度的二次效应对特定生长率有极显著影响(P0.01),特定生长率随着亚硝酸盐或密度的上升呈先上升后下降的变化。亚硝酸盐与养殖密度之间存在互作效应(P0.05)。亚硝酸盐浓度和养殖密度分别为1.65mg/L和3.28尾/10L时,肝脏超氧化物歧化酶(SOD)和过氧化氢酶(CAT)的活力同时较高。亚硝酸盐与养殖密度的一次效应对MDA含量和两种酶活力均有显著影响(P0.05),二次效应对两种酶活力的表达有极显著影响(P0.01);亚硝酸盐与密度对SOD和CAT活力有互作效应,高浓度亚硝酸盐与高密度环境会抑制SOD和CAT活力的表达,增加肝脏MDA含量。因子与响应值间二次多项回归方程的决定系数分别达到0.9384、0.9004、0.9520和0.9650(P0.01),可用于响应值预测;亚硝酸盐含量比养殖密度对养殖鱼的生长影响更为明显。建议在罗非鱼集约化养殖中,保持溶氧充足,降低氧化胁迫,提高罗非鱼的生长与抗氧化力。

USING RESPONSE SURFACE METHODOLOGY TO DETERMINE EFFECTS OF CHRONIC NITRITE EXPOSURE AND STOCKING DENSITY ON GROWTH OF GIFT TILAPIA OREOCHROMIS NILOTICUS JUVENILES

We conducted a two-factor central composite rotatable design(CCD) in response surface methodology(RSM) to study the specific growth rate(SGR), content of malondialdehyde(MDA), and activities of antioxidant enzymes(superoxide dismutase:SOD and catalase:CAT) in liver of GIFT tilapia Oreochromis niloticus juvenile. The critical factors selected were nitrite(0.02-2.8mg/L) and density(1-5 ind./10L), under which the linear, quadratic, and reciprocal effect of chronic nitrite exposure and stocking density were determined in regression. The fish(2.97±0.06)g body weight,(4.45±0.12)cm body length] were grouped accordingly for experiment that lasted 35 days. The results show that the linear effect of nitrite and the density and the quadratic effect of density were significant on the SGR(P<0.05). In addition, the effect between nitrite and the density on the growth(P<0.05) was significantly reciprocal. The nitrite and the density had significant linear effects on MDA and two enzymes(P<0.05); and had very significant quadratic effects on the two enzymes(P<0.01). There was a significant reciprocal effect on SOD and CAT activities. Therefore, high external nitrite concentration and high stocking density could depress the expression of SOD and CAT activities while promoted MDA. Moreover, the coefficients of correlation in all regressional equations were>0.9(P<0.01). Nitrite concentration was more influential on the fish growth than the stocking density. It is suggested that the density should be kept reasonably for adequate dissolved oxygen supply, which can reduce oxidative stress and improve growth and disease resistance of tilapia.