Effects of Stocking Density on the Growth and Physiology of Adult Turbot and Changes in Water Quality

Abstract:

To investigate the effects of various densities on the growth, physiology and water quality of adult turbot in a recirculating aquaculture system, the adult turbots with the initial average weight (580.9±44.65) g were cultivated at one of the following three stocking densities: low (14.30 kg/m2, Group A), medium (20.49 kg/m2, Group B), and high (31.32 kg/m2, Group C) for 120 days. The survival rate, weight change, food coefficient and blood lysozyme level, as well as the changes in total ammonia (TAN), nitrite nitrogen (NO2-N), and COD in aquaculture water were measured. The results showed that the stocking densities of A, B and C group were 30.09 kg/m2, 41.30 kg/m2 and 60.07 kg/m2, respectively at 120 days. The survival rates of three groups were all over 95%. The net weight gain in each group varied significantly (P <0.01) with the highest in Group C. Feed conversion rates (FCR) of cross the three groups were 0.73, 0.75 and 0.82, respectively, which were positively associated with stocking density. Blood lysozyme level in Group C was increased at 5 d; it began to decline at 20 d and then decreased markedly at 40 d compared with that in Group A (P<0.01). During the entire experiment, the recirculating aquaculture systems were stable and the stocking densities had significant effects on the TAN, NO2-N and COD of water quality index (P<0.05). The increase of the stocking density significantly increased water quality indexes; however, it did not exceed the fishery water quality standards.