The effects of stocking density on growth and physiological indices of grouper Epinephelus awoara in recirculating aquaculture

The grouper Epinephelus awoarea with an initial body weight of(108.7±4)g were reared in a recirculating system at stocking rate of 10,20,or 30 kg/m3 for 50 days with triplication to evaluate the effects of stocking density on growth,enzyme activity in liver and gill,and blood physiological indices.The results showed that: 1) There were significantly lower weight gain(WG) and specific growth rate(SGR) at a stocking density of 30 kg/m3 than at 10 kg/m3 and 20 kg/m3(P0.05),with the maximal food conversion ratio at stocking density of 30 kg/m3.2) The glutamate-oxaloacetate transaminase(GOT) and glutamate-pyruvate transaminase(GPT) activities in the serum and the GPT activities in the liver and gill were found to be increased with the stocking density,with significantly different between the two groups(P0.01).3) There was an increase in the plasma cortisol level as the culture density was increased(P0.01),while the count of red blood cells was found to be decrease(P0.01).There was significantly lower hemoglobin level in 30 kg/m3 group than that in other two groups(P0.05).4) There was no significant difference in muscle nutrition compositions among three groups(P0.05).Conclusively,over high density is unfavorable to the growth of the grouper,and 20 kg/m3 is considered as optimum stocking density in terms of the economical profits.