Replacement of fish meal by plant proteins in diets for rainbow trout (oncorhynchus mykiss): effect of the quality of the fishmeal based control diets on digestibility and nutrient balances

A great deal of attention has been paid to the replacement of the high levels of fishmeal present in commercial diets by alternative animal and vegetable protein sources. There are some contradictory data on the effects of partial or total replacement of dietary fishmeal especially regarding vegetable protein sources. The effect of technological treatments applied to the vegetable materials and the quality of the control diets are the reasons for these contradictory results. A ten week growth trial was conducted to study the effect of partial or total replacement of fishmeal by plant proteins in diets for rainbow trout. For this purpose, four practical diets were formulated: a fishmeal-based control diet, which included a brown fishmeal as the only protein source (diet C1); another diet where 5% of the brown fishmeal protein was replaced by a fishmeal protein concentrate (CPSP; diet C2); and two other diets where 50% (diet C50) and 100% (diet C100) of the fish meal protein was replaced by plant protein sources (soybean meal, fullfat soybean and corn gluten meal). The results of the growth trial showed that 50% of the fishmeal protein can be replaced by vegetable protein sources with no adverse effects on growth and feed utilization when diet C1 was used as control. However, using diet C2 as control, weight gains of trout fed the other diets were all significantly lower. Nitrogen and phosphorus balances were also estimated and results are discussed regarding the effect of diet quality on environmental impact.