Effects of soybean meal processing treatments on growth performance, nutrient digestibility, nitrogen and phosphorus excretion in red swamp crayfish, Procambarus clarkii

In this study, growth performance, apparent digestibility coefficients, phosphorus and nitrogen excretion were determined in red swamp crayfish (Procambarus clarkii) (5.39 ± 0.12 g) for four soybean products: soybean meal (SBM), soybean meal diets supplemented with 1000 IU/kg phytase (SBM + P), extruded soybean meal (ESBM) and fermented soybean meal (FSBM). The results showed that compared with the SBM diet, the crayfish fed the SBM + P and FSBM diets showed significantly higher specific growth rate (SGR) and lower feed conversion ratio (FCR) (P < 0.05). The highest and lowest dry matter (DM) digestibilities were observed in SBM + P and ESBM diets, respectively (P < 0.05). Differences in crude protein (CP) and gross energy (GE) followed differences in DM digestibility. SBM + P had the highest phosphorus digestibility, and ESBM had the lowest. The highest crude lipid (CL) digestibility coefficient was observed in FSBM, followed by SBM + P, and the lowest in ESBM (P < 0.05), which was similar to SBM. And the ESBM group had the highest phosphorus content in sediments (P < 0.05); while the highest nitrogen content was observed in SBM group, which was significantly higher than SBM + P group (P < 0.05). The water phosphorus contents in SBM and ESBM groups were significant higher than SBM + P group at 48 h (P < 0.05), but there were no significant differences among the water nitrogen content of all groups (P > 0.05).