Effects Of Dietary Soy Protein Concentrate Levels On Feed Intake, Growth Performance, Digestion And Protein Metabolism Of Juvenile Darkbarbel Catfish Pelteobagrus Vachelli

An 70 day feeding trial was conducted in recirculation rearing system to examine the effects of dietary soy protein concentrate (SPC) levels on survival, growth, digestion and protein metabolism of juvenile darkbarbel catfish Pelteobagrus vachelli. (initial weight 1.54±0.01g). During the experimental period, water temperature, dissolved oxygen and pH value were maintained at 21-26°C, 7-9 mg/L and 6.8-7.6, respectively. Total ammonia–nitrogen was less than 0.2mg/L and nitrite level was below 0.09 mg/L. Six isonitrogenous (crude protein 39%) and isoenergetic (19.5 kJ g?1) practical diets were formulated by replacing 0 (the control), 20, 40, 60, 80 and 100% protein from fish meal with SPC. Each diet was randomly fed to triplicate groups of fish, and each cage was stocked with 40 fish. Fish were fed twice daily (07:00 and 18:00) to apparent satiation. Results of the present study are presented as follows:1. Survival rate ranged from 97.5% to 100%, however, no significant differences were observed in survival among dietary treatments with the increasing dietary SPC levels (P>0.05).2. There were no significant differences in feed intake (FI) among fish fed the diets with 0, 20, 40 and 60% protein from SPC and FI in fish fed the diets with 80 and 100% protein from SPC were significantly lower than the control diet (P<0.05). Specific growth rate (SGR) also decreased with increasing dietary SPC. No significant differences in SGR of fish fed the diets with or less than 60% protein from SPC were observed. SGR in fish fed the diet with 100% protein from SPC was significantly lower than other groups (P<0.05). Feed conversion ratio (FCR) followed the same pattern as FI.3. Results of whole-body composition analysis showed that body protein ranged from 48.2% to 48.8%; body lipid ranged from 41.4% to 43.8%; ash ranged from 8.9% to 9.3% and no significant differences were observed among dietary treatments (P>0.05).4. The apparent digestibility coefficients of dry matter, protein and lipid and the activities of digestive enzymes and protein metabolism enzymes (pepsin, trypsin and aminotransferases) decreased with increasing dietary SPC levels (P<0.05).5. With increasing dietary SPC levels, the histological structure in liver and hid gut integrity of P. vachelli juvenile were destroyed. Additionally, enteritis in the distal intestine was found in experimental fish fed the diet with 100% protein from SPC.Results of the present study suggested that SPC could substitute with or less than 60% fish meal protein without influencing the growth performance and protein metabolism of Pelteobagrus vachelli juvenile. The higher substitution levels with SPC induced negative influences on feed intake, growth, digestion and protein metabolism of Pelteobagrus vachelli juvenile.