Evaluating two different additive levels of fully autolyzed yeast, Saccharomyces cerevisiae, on rainbow trout (Oncorhynchus mykiss) growth performance, liver histology and fatty acid composition

Abstract

This study examined the effects of fully autolyzed Saccharomyces cerevisiae (ASC) on rainbow trout (Oncorhynchus mykiss) growth performance, liver histology and fatty acid composition. 2700 rainbow trout (4.9 ±0.1 g mean weight) were acclimated to rearing conditions and then randomly divided into three groups of triplicate cages. Rainbow trout were feed with three different doses of ASC (0 (control), 1 ‰ and 2 ‰) for 70 days. At the end of the study, growth performance, liver histology, fatty acid composition and survival rate were determined. Feed conversion ratio was significantly decreased and specific growth rate was increased (P<0.01) on 2‰ ASC added group compared to other groups. No differences were observed among group’s liver histology. Whole-body proximate composition showed no differences among groups (P>0.05) except in fat content, which was enhanced in both ASC groups compared to control (P<0.05). The fatty acid composition of fish fillets differed only marginally among the experimental groups. The muscles of fish fed the diets with ASC had a significantly decreased in 18:0 (P<0.05) and an increased in 15:1 (P<0.01) content compared to control groups. The content of n-3 fatty acids and DHA/EPA ratio were not affected by ASC addition. In conclusion, the results of the study indicate that 2‰ supplementation level of the ASC showed beneficial effects on the growth performance without affecting moisture, protein and ash content of rainbow trout.