Effect Of Stocking Density On Growth And Immune In Flounder Reared In Re-circulating And Flow Through Rearing Systems

With the rapid development of economy in our country in recent years, industrial wastewater and domestic sewage emissions increase greatly, which cause water quality pollution that have a serious impact on aquaculture. A new kind of higher density and super-intensive culture mode-closed re-circulating aquaculture were gradually popularized. It is advantageous to make use of resources, reduce pollution of the environment, cut off dissemination of disease and increasing the farming yield as well, which was commended as a new technique revolution of the fish farming. In this paper, we mainly study the stocking density effect on growth, digestive enzymes and immune, while compared the growth,digestive enzymes and immune of Cynoglossus semilaevis Gunther between re-circulating aquaculture and flow culture, the main conclusions are as follows:1. Effect of stocking density on growth and immune in Scophthalmus maximus reared in flow culture systemWe set five different experiment groups in the initial stocking densities at 1.76,5.27,7.03,8.78,10.54 kg/m2 respectively. After 30 days, result showed that the growth rate decreased but the feed conversion rate significantly increased with the stocking density higher. There was no significantly difference for SGR,CF,CV with the stocking increasing. The number of blood corpuscle and AKP,ACP activity both raised with the stocking increasing, but there was no significantly difference.2. Effect of stocking density on growth and immune in Scophthalmus maximus reared in re-circulating aquaculture systemWe set four different experiment groups in the initial stocking densities at 0.66,1.26,2.56,4.OOkg/m2 respectively, every group has three parallel groups. The experiment lasted for 75 days with final stocking densities at 4.67,7.25,14.16,17.77 kg/m2 respectively. Result showed that the stocking densities for turbot had significant influences on SGR,WGR,average daily gain,rate of daily gain and feed coefficient. With the stocking density increasing, SGR,WGR,rate of daily gain decreased,but feed coefficient increased. The uniformity of weight distributing among experiment groups decreased with increasing density. The stocking density had negative relationship to liver organ coefficient. The concentration of ammonia-nitrogen in the re-circulating aquaculture pond was significant (P<0.01) lower than that in the flow cultured pond, but the concentration of nitrite-nitrogen was higher than that in the flow. The average removal rates of the ammonia-nitrogen by bio-filter were 33.32%, but that of the nitrite-nitrogen were only 4.23%.3.Comparing of digestive enzymes and immune of Cynoglossus semilaevis Gunther between re-circulating aquaculture and flow cultureDuring the 5 months experiment, the mortality rate was low in both system,2.88% in the RS and 1.49% in the FTS. Stocking density increased progressively from 14.7 to 37.0 kg/m2 in the RS and from 5.9 to 13.5 kg/m2 in the FTS. The relative growth rate was 158.5%in the RS, compared to132.8%in the FTS. Average monthly weight gain was better in the RS than FTS,120g and 51.8 g respectively. There was significant difference(P<0.05)between the two rearing systems at the end of the experiment. NH3-N concentrations were much lower in the RS (0.036mg/L) than in the FTS(0.152mg/L) and conversely NO2--N concentration(0.114mg/L) was more than sixth higher than that in the FTS(0.016mg/L). There were significant differences(P<0.01)between the RS and the FTS water quality. The AKP, ACP, LSZ activity in blood serum of Cynoglossus semilaevis Gunther were no significantly difference (P>0.05) between re-circulating aquaculture and flow culture, but amylase activity in stomach and intestinal of Cynoglossus semilaevis Gunther in re-circulating aquaculture were significant (P<0.01) higher than those in flow culture, protease activity in stomach and trypsin activity in intestinel were significant (P<0.05) higher than those in flow culture.