Brewer's yeast as a diet supplement in carp aquaculture: impact on production coefficients and haematological and biochemical plasma parameters

While brewer's yeast (Saccharomyces cerevisiae), a rich source of proteins and B vitamins, is commonly used as an animal feed supplement, its use in aquaculture has been limited. Here, we assess its impact on 192 individuals of common carp (Cyprinus carpio) production and haematological and biochemical parameters from blood plasma using a control group fed commercial feed with 20% soybean meal and three test groups fed commercial feed with (i) 17.50% soybean + 2.50% brewer's yeast (group B-2.5), (ii) 15% soybean + 5% yeast (group B-5) and (iii) 10% soybean and 10% yeast (group B-10). At the end of the experiment, all fish were weighed and measured and subsequently blood samples were taken from eight fish in each tank. There was a significant increase in total length (3%) and weight (5.37%) in group B-5. While fish muscle nitrogenous matter and protein efficiency ratio increased slowly across experimental groups, Fulton's and Clark's condition factors changed minimally (range 2.73-2.89%). Apparent net protein utilisation increased to 17.63% in B-10, suggesting that increasing yeast levels result in improved nitrogen utilisation. All fish muscle fat levels were within optimal range (4.16-4.68%) and, while there was a significant increase in erythrocytes in B-5 (up 0.40 T.L-1), haemoglobin levels increased only slightly in B-5 and B-10 (average 4.50 g.L-1) and B-10 had the lowest number of leukocytes (6.8 G.L-1). No significant changes were recorded in blood plasma biochemical parameters. Our results suggest that a 5% brewer's yeast feed supplement represents a useful protein source for carp aquaculture.