Partial replacement of fishmeal by brewers yeast ( Saccaromyces cerevisae) in diets for sea bass ( Dicentrarchus labrax) juveniles

Abstract

A trial was conducted to test the effect of partial replacement of fishmeal (Danish LT fishmeal—the only protein source in the control diet) by brewers yeast, in isonitrogenous (48% CP) and isoenergetic (22 MJ kg −1) diets for sea bass juveniles with an initial average weight of 12 g. Diets were formulated to include 0%, 10%, 20%, 30% or 50% of dietary N from yeast (diets D0, D10, D20, D30, D50, respectively); another diet supplemented with methionine (diet D50M) was also prepared. Each diet was distributed by hand to satiation to duplicate groups of 25 fish and the growth trial lasted 12 weeks. During the trial, feed intake (g kg −1 day −1) was identical in all groups. At the end of the trial growth rate was not significantly different among groups, except for the D50M diet, which was significantly lower than diet D30. Feed conversion was better for diets D10, D20 and D30, containing yeast than for the control diet. N retention (% N intake) was significantly higher in fish fed diets containing yeast (except for the D50M diet) than in those fed the control diet. There were no significant differences among groups in energy retention (% E intake). The protein content of the fish was significantly higher in fish fed diets containing yeast (except for the D50M diet) than in those fed the control diet. Apparent digestibility of the diets was determined in a separate trial with fish weighing 62 g. Feces collection was performed according to the Guelph system. Apparent digestibility coefficients of dry matter and energy significantly decreased with the increase of dietary yeast level. ADC of protein was significantly lower for the D50 diet than for the other diets. Results of this trial indicate that brewers yeast can replace 50% of fishmeal protein with no negative effects in fish performance. Moreover, the inclusion of up to 30% brewers yeast in the diet improved feed efficiency. There was no beneficial effect of supplementing the brewers yeast diets with methionine.