Growth performance, body composition and phosphorus availability of juvenile grass carp (Ctenopharyngodon idellus) as affected by diet processing and replacement of fishmeal by detoxified castor bean meal

The objectives of the study were to determine the effect of diet processing and replacement of fishmeal by detoxified castor bean meal (DCBM) on growth performance, body composition and phosphorus availability of juvenile grass carp (Ctenopharyngodon idellus, initial body weight 9.74 ± 0.03 g). Three replacing levels (0, 40 and 100% of fishmeal protein were replaced by DCBM protein) were designed, which were processed by pelleting machine or extruder, respectively. Y₂O₃ (1 g kg^?1) was used as inert marker for apparent digestibility coefficients (ADC) measurement. The results showed that DCBM replacement level significant decreased specific growth rate, feed conversion efficiency, protein efficiency ratio and feed intake. Phosphorus excretion was reduced because of lower intake of apparently absorbed phosphorus and higher ADC of total phosphorus with higher inclusion level of DCBM; extrusion significantly increased ADC of dry matter while decreased ADC of total phosphorus and intake of apparently absorbed phosphorus compared with the pellet diet. The DCBM replacement levels, processing methods and interaction factor had significant effects on the whole body composition. According to the results of this study, it is concluded that juvenile grass carp can accept the extruded diets containing 50 g kg^?1 DCBM (<16 mg kg^?1 ricinine).