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USING RESPONSE SURFACE METHODOLOGY TO DETERMINE EFFECTS OF CHRONIC NITRITE EXPOSURE AND STOCKING DENSITY ON GROWTH OF GIFT TILAPIA OREOCHROMIS NILOTICUS JUVENILES
Author(s): 
Pages: 1166-1174
Year: Issue:  5
Journal: Oceanologia et Limnologia Sinica

Keyword:  Oreochromis niloticusnitritestocking densityresponse surface methodologygrowthantioxidant capacity;
Abstract: 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.
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