Optimal dietary protein to energy ratio for juvenile peanut worm Sipunculus nudus Linnaeus

The optimal dietary protein to energy (P/E) ratio for juvenile peanut worm Sipunculus nudus Linnaeus (initial average weight 46.16 ± 0.07 mg) was determined using practical diets in a 3 × 3 factorial experiment. Three dietary protein levels (38, 43, and 48 %) and three lipid levels (6, 9, and 12 %) were tested, yielding P/E ratios of 19.5–26.4 mg protein kJ−1. Each diet was fed to juveniles in three plastic tanks (65 × 55 × 45 cm) for 56 days. S. nudus juveniles fed a diet containing 43 % protein and 9 % lipid, yielding a P/E ratio of 23.1 mg protein kJ−1, presented the highest specific growth rate among the treatments (P < 0.05). The highest protease and lipase activities were observed in S. nudus juveniles fed a diet with a P/E ratio of 23.1 mg protein kJ−1. Carcass moisture and ash contents were not significantly affected by the dietary P/E ratio (P > 0.05). Carcass protein content improved as dietary protein increased at each lipid level, and carcass lipid content improved as dietary lipid increased at each protein level. The results indicate that feeding S. nudus a diet containing 43 % protein and 9 % lipid, with a P/E ratio of 23.1 mg protein kJ−1, leads to optimal growth performance.