Responses of growth rates and growth hormone levels of African catfish (Clarias gariepinus) to stocking density

In order to estimate responses of growth rate and growth hormone of Clarias gariepinus to stocking density, fish (initial weight ۳۰.۷۱ ± ۰.۸۹ g) were stocked in ۱۲۰-L tanks at densities of ۳۵, ۶۵, ۹۵, and ۱۲۵ kg/m۳ for ۶۰ days. On day ۳۰ and ۶۰, the fish growth rates were measured, pituitary growth hormone (GH) mRNA levels and serum GH concentrations were examined by real-time qPCR and ELISA technique, respectively. From day ۰ to day ۳۰, there were significant decreases in specific growth rates and relative weight gains at higher densities (۹۵ and ۱۲۵ kg/m۳) compared to that at lower densities (۳۵ and ۶۵ kg/m۳), whereas no significant effects of stocking density on the two indexes during the day ۳۰−۶۰ were detected. On day ۳۰, GH mRNA levels were unaffected by stocking density, while on day ۶۰, GH mRNA levels were significantly lower at the density of ۱۲۵ kg/m۳ than in the two lower densities. Serum GH concentration increased with decreasing stocking densities but only significantly between ۳۵ kg/m۳ and the other treatments on day ۳۰. However, there were no significant differences between two lower densities as well as between ۶۵ kg/m۳ and ۹۵ kg/m۳ treatments on day ۶۰. These results implied that effect of stocking density on SGR and RWG of C. gariepinus weren’t uniform in different growth periods and a weak positive correlation was observed between growth rate and GH in C. gariepinus in the present study.