Effects of dietary soybean protein levels on metabolic response of the southern catfish, Silurus meridionalis

A closed respirometer was used to measure oxygen consumption of the southern catfish Silurus meridionalis fed with six isonitrogenous (48% crude protein) diets replacing 0%, 13%, 26%, 39%, 52% and 65% fish meal (FM) protein by soybean meal (SBM) protein, in order to investigate the effects of dietary soybean protein level (SPL) (replacing FM) on metabolic rates of the southern catfish. The results showed that there were no significant differences in routine metabolism among dietary treatments. Either the total metabolic rate or specific dynamic action (SDA) was positively correlated with assimilated food energy at each diet, respectively (P < 0.05). The SDA coefficient (means the energy spent in metabolism per unit of assimilated dietary energy) significantly increased with increasing dietary SPL (P < 0.05). Fish fed the diet with 13% SPL had a significantly lower SDA coefficient (0.1528) than fish fed the diet with 52% or 65% SPL (0.1826 or 0.1932) (P < 0.05). However, there were no significant differences in SDA coefficient among fish fed the diets with 13%, 26% and 39% SPL (P > 0.05). Results of the present study suggested that an imbalance of essential amino acids at higher dietary SPL resulted in more energy channeled into metabolism, and subsequently increased the SDA coefficient.