The effect of food type (formulated diet vs. natural) and fish size on feed utilization in common sole, Solea solea (L.)

This study compares the effect of food type (formulated diet vs. natural food) and fish size on protein and energy utilization efficiencies for growth in common sole, Solea solea (L.). Replicate groups of common sole (mean initial body weight ± SD was 45.7 g ± 2.1 and 111.2 g ± 4.2) received the diets at five (natural feed) or four (formulated diet) feeding levels. The protein utilization efficiency for growth (kgCP) was higher (P > 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.40 and 0.31). Likewise, the energy utilization efficiency for growth (kgGE) was higher (P = 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.57 and 0.33). The protein maintenance requirement was not different between food types (P = 0.64) or fish size (P = 0.41) being on average 0.82 g kg−0.8 day−1. The energy maintenance requirement was not different between food type (P = 0.390) but differed between fish size (P = 0.036). The gross energy maintenance requirement of small common sole was 35 kJ g−0.8 day−1. The gross energy maintenance requirement of large common sole was 25 kJ g−0.8 day−1. In conclusion, the low growth of common sole fed formulated diets was related to reduced feed utilization.