Evaluation of a yeast, a bacterium and an alga as a protein source for rainbow trout: I. Effect of protein level on growth, gross conversion efficiency and protein conversion efficiency

Abstract

A yeast ( Candida lypolytica), a bacterial ( Pseudomonas sp.), and an algal ( Spirulina maxima) protein have previously been shown to be tolerated by rainbow trout ( Salmo gairdnerii) at levels of 20 and 40% in compound feeds fed for 12 and 10 weeks successively, during which time no pathological disturbances were observed. In the present work, these single-cell proteins were examined for their effect, at four levels of inclusion in the diet, on growth, gross conversion efficiency and protein conversion efficiency. The appetite quotients quantified as metabolizable energy intake varied significantly from that of a commercial control diet, being higher for the yeast and lower for the bacterial and algal proteins. Yeast protein was the best utilized for growth and gave generally higher FCE (food conversion efficiency) values than bacterial and algal protein, maximum growth and FCE occurring at 35% protein inclusion. Growth rate and FCE reached an optimum at a 25% level for diets containing bacterial protein, while diets containing algal protein up to the 25% level did not appear to promote adequate growth. The maximum protein efficiency ratio occurred at the 25% level in diets containing yeast and bacteria, and at the 30% level for algal protein. The maximum PER (protein efficiency ratio) achieved for bacteria, algae and yeast was 1.88, 1.17 and 2.12, respectively.