THE NUTRITION OF SILURUS MERIDIONALIS: EFFECTS OF DIFFERENT LEVELS OF DIETARY SOYBEAN PROTEIN ON GROWTH

A growth experiment was conducted in a recirculating rearing system on juvenile of the southern catfish, Silurus meridionalis, at 27.5±0.02℃. Six isonitrogenous (48% protein) and isoenergetic (20KJ/g gross energy) diets, with soybean meal protein (SP) replacing 0%, 13%, 26%, 39%, 52% and 65% of fish meal protein (FP), were formulated to examine the effects of different levels of SP on growth and feed conversion efficiency. The results showed that the specific growth rates (SGRs) in fish fed the diets with 13% and 26% of SP were significantly higher than those of control group (P0.05), while the SGRs in fish fed the diets with 52% and 65% of SP were significantly lower than those of control group (P0.05). The SGRin fish fed the diet with 39% of SP was higher compared with control group, but the difference was not significant (P0.05). There were no significant differences in SGRamong fish fed the diets with 13%, 26% and 39% of SP (P0.05). The changes of feed conversion efficiency (FCE), protein efficiency ratio (PER) and protein productive value (PPV) among different tested groups followed the similar pattern as that of SGR. The results indicated that 39% of FP could be replaced with SP in the diet for the southern catfish and excessive inclusion of dietary SP will result in poor growth and low feed conversion efficiency. Discussion in this paper suggested that the main limitations in use of dietary SP for the catfish were due to its low digestibility and imbalance of amino acid.