Most probiotic yeast supplement in fish exhibit beneficial effect at ≤1% of the dietary proportion. This study aimed at evaluating the specific effects of Lypomyces starkeyi CB1807 yeast strain supplemented at ≤1% of dietary proportion on the performance of juvenile red sea bream (Pagrus major, 1.9 ± 0.04 g). Five diets were supplemented with yeast at graded levels of 0% (control diet ‘CD1’), 0.05% (D2), 0.1% (D3), 0.5% (D4), and 1.0% (D5). After 45 days of feeding trial, significant (P<0.05) improvement was detected on final body weight (FBW) and body weight gain (BWG) in fish fed D3 and D5 compared to control. Low values of total cholesterol (T-Cho) and aspartate aminotransferase (AST) were recorded in fish groups fed on D2, D4, and D5, respectively. Fish fed on D3, D4 and D5 diets showed high (P<0.05) values of serum, mucus and liver lysozyme compared to control. Fish fed on D5 showed high values of total immunoglobulin (Ig) compared to control. Fish fed on D2 showed strong correlation with biological antioxidant activity (BAP), superoxide dismutase (SOD) and catalase activity (CAT). The biological antioxidant potential (BAP) activity in fish fed on D2 was significantly higher compared to control (P<0.05). The reactive oxygen metabolites (d-ROM) were significantly lower in fish fed on D2 and D3 compared to CD1 (P<0.05). Peroxidase activity was improved significantly (P<0.05) in fish fed on D3, D4 and D5 compared to control. The tolerance ability (LT50) of fish fed on D5 against low salinity stress was significantly higher compared to control (P<0.05). It was concluded that dietary benefits of spent L. starkeyi yeast at ≤1% showed considerable improvement in antioxidant capacity in red sea bream, P. major.
