Effect Of Stocking Density On Growth And Protein Metabolism Of Scophthalmus Maximus L. In Recirculating Aquaculture System

In this paper, the effect of stocking density on the growth performances of turbot(Scophthalmus maximus L.) in recirculating aquaculture system(RAS) was investigated. We also studied the differences of the water quality indicators on three densities during the whole experiment; this study had evaluated the effect of stocking density on digestive enzyme activity and protein metabolism of turbot(Scophthalmus maximus L) in recirculating aquaculture system(RAS).In this experiment, turbot with an initial body weight of(186±2.0)g were reared at three different initial densities(low 9.4±0.2,medium 13.6±0.8,high 19.1±1.3 kg/m2)for 120 days. Final densities were 26.1±1.2,38.2±2.5,52.3±3.6 kg/m2,respectively. The result shows that: Fish held at the highest density showed lower(p<0.05) weight gain rate(WGR), specific growth rate(SGR),condition factor(CF) and Protein efficiency ratio(PER) at the conclusion of the study than fish held at lower densities; but the highest density group had higher(p<0.05) feed coefficient rate(FCR) than fish held at lower densities.The recirculating aquaculture system(RAS) operationed stability during the experiment, the water quality as follows: the changes of density group during the experiment, he tgroups of the system of total ammonia nitrogen(TAN), nitrite-N(NO2--N) and phosphate-P(PO4--P) at the early stages of the experiment began to appear larger fluctuation, and the overall rise, and COD has been a slow and steady rise, at the end of the experiment, high density group of TAN and PO4--P concentration was significantly higher than that of medium density and low density group, but the content of NO2--N and COD in no significant difference between the density of the three groups.The total protease(TMP) and amylase(AMS) activities of highest density group were significantly higher(p<0.05) than lower densities group, and three groups did not differ significantly in lipase(LPS) activities. As stocking densities increased, the glutamate dehydrogenase(GDH) activities were significantly increased and the aspartate transaminase(AST) and leucine aminopeptidase(LAP) activities were significantly decreased, but the alanine transaminase(ALT) activities were not significantly affected by density.It is concluded that increasing stocking density can improve the production of farming in RAS, but high stocking density may impact growth, digestive enzyme activity and protein metabolism.