preliminary study on the effects of dietary supplementation of brewers yeast and nucleotides, singularly or in combination, on juvenile red drum (Sciaenops ocellatus)

This study was designed to evaluate the effects of dietary supplementation with brewers yeast (Brewtech) and nucleotides (Optimun), either singularly or in combination, on red drum growth, body composition, stress responses and possible resistance to Amyloodinium ocellatum infection. Juvenile red drum (approximately 1 g initially) fed practical fish-meal-based diets for 6 weeks had similar weight gain regardless of whether the diet was unsupplemented (basal) or supplemented with brewers yeast (2% of diet), nucleotides (Optimun at 0.2% of diet) or both brewers yeast (2% of diet) and nucleotides (Optimun at 0.2% of diet). Dietary effects on hepatosomatic index, intraperitoneal fat ratio or whole-body composition were not significant, except that fish fed the singular nucleotide supplement had a significantly higher whole-body lipid content compared with fish fed the basal diet. No significant dietary effects on cortisol response were observed after a 15 min confinement stress test perhaps because of the extreme variation among individual fish. Subsequently, in situ challenge by co-habitation with A. ocellatum caused 100% mortality regardless of dietary treatment within a 48 h period. It is concluded that dietary supplementation of brewers yeast and nucleotides did not promote enhanced growth or improved cortisol response and resistance to uncontrolled amyloodiniosis in juvenile red drum, at least at the tested dosages.