Incorporation of a mixture of plant feedstuffs as substitute for fish meal in diets of juvenile turbot (Psetta maxima)

A study was designed to evaluate the maximum level of substitution of fish meal in diets for turbot when a mixture of feedstuffs of plant origin was used and when the amino acid profile was adjusted to reflect amino acid profile of a reference fish meal based diet. Five diets were formulated: a reference diet (FM40) containing 40% fish meal and four other diets (FM30, FM20, FM10 and FM0) in which protein from fish meal was substituted by protein from lupin, corn gluten and wheat gluten meal. Amino acids profile of each diet was balanced by addition of crystalline amino acids. Turbot, initially weighing 26 g were fed these diets for 12 weeks and growth parameters were recorded. Protein (96%), energy (83%) and dry matter (73%) digestibility were very high in all diets tested. Feed intake was significantly decreased by the incorporation of plant protein in diets (from 10.2 g/kg ABW/day to 8.2 g/kg ABW/day in fish fed diets FM40 and FM0, respectively), growth rate was only affected in fish fed diets FM10 and FM0 (respectively, 2.2 and 1.9%/day against an average of 2.4%/day for the other treatments) and no effect on feed utilisation was observed. The whole body composition of fish and the nitrogen retention were significantly negatively affected when dietary fish meal incorporation was equal or less than 20% diet. Activities of alanine amino transferase (ALAT) were significantly increased by the dietary incorporation of plant protein. These results suggest that a sizeable amount of fish meal can be replaced by plant feedstuffs in diets of turbot when an adequate mixture of plant feedstuffs along with amino acid supplementation are used. (C) 2004 Elsevier B.V. All rights reserved.