Effects of stocking density on growth, physiology and immune parameters of Carassius cuvieri reared in greenhouse recirculating aquaculture system with constructed wetlands as filters

To investigate the effects of stocking density on the growth, organ coefficient, physiology-immune parameters in serum and the resistance against Aeromonas hydrophila of Carassius cuvieri reared in an indoor recirculating aquaculture system with 2-stage constructed wetlands as filters, we cultured C.cuvieri for 68 d at various stocking densities of 2 kgm-3, 4 kgm-3, 8 kgm-3 and 16 kgm-3 (each density hadtwo parallel groups). The results show that: 1) no significant difference was found among the four density-groups ongrowth and organ coefficients of C.cuvieri ; 2) compared with 2 kgm-3 density group, the concentration of malondialdehyde (MDA) in serum of 16 kgm-3 density group significantly increased, while the activities of serum lysozyme (LSZ), acid phosphatase (ACP) and alkaline phosphatase (AKP) significantly decreased. The activity of superoxide dismutase (SOD) andconcentration of total protein (TP) were not significantly different although there was a certain degree of elevation; 3) the resistance of C.cuvieri against A.hydrophila was weaker in higher-density groups than that in lower-density groups. It is revealed that if considering growth as an indicator, stocking density of C.cuvieri could increase to 16 kgm-3 when reared in indoor recirculating aquaculture system with 2-stage constructed wetlands as filters. However, it should be noted that there would be adverse effect of the immunity of C.cuvieriat such a high stocking density.