Formulation of low phosphorus loading diets for carp (Cyprinus carpio L.)

Abstract

This study focuses on reducing total phosphorus loading (T-P) from carp culture through improved feed formulation. Since phosphorus (P) contained in fish meal (FM) mainly in the form of tricalcium phosphate is not available to carp, which lack a stomach, the reduction of FM from their diets is effective for lowering T-P. Thus in this experiment, six diets (crude protein 3.5 kcal g−1) were designed by substituting FM (10%−25%) with alternate protein ingredients such as poultry feather meal (PFM; 5%−10%), blood meal (BM; 5%−7%) and defatted soybean meal (dSBM; 4%−9%). All diets followed the Kasumigaura ‘Feed Standard’. The total dietary P was 1.0%−1.4% and water extractable P available to carp was 0.66%−0.71%, the levels meeting the dietary requirement of carp. A feeding trial was conducted with juvenile carp (4.6 ± 0.7 g) for 12 weeks at a mean water temperature of 23.7°C. The T-P loading from fish fed the different diets was estimated based on absorption and retention of dietary P. Growth performance corresponded to increasing levels of FM inclusion, being highest in the fish fed 25% FM diet; however, the decrease in T-P was achieved at the lower FM levels. The T-P (based on P retention) ranged from 8.9 to 11.7 kg t−1 production, much lower than that from the commercial diets (9.1–26.4 kg t−1 production). These results indicated that the reduction of FM levels in carp diets to 15%−20% through the combined use of PFM, BM and dSBM effectively lowered T-P. Moreover, the formulated diets were also found to be better than commercial diets in lowering the N loading from carp culture.