Dietary nucleotides have been shown to benefit many physiological and nutritional functions in higher
vertebrates and fish. Therefore, a 6-week feeding trial was conducted to evaluate the effects of graded
levels of a commercial nucleotide product on growth performance, immune responses and intestinal
morphology of juvenile red drum (initial average weight of 7.1 g). The basal diet was formulated to
contain 40% protein, 10% lipid and a digestible energy level of 3.5 kcal g1. Two levels of nucleotide
(Ascogen P, 0.5% and 1% of diet) were added to the basal diet with menhaden fishmeal and menhaden
oil adjusted to provide isonitrogenous and isolipidic diets. Nucleotide supplementation tended to
improve weight gain and survival of red drum, but not at a significant level. Neutrophil oxidative radical
anion production and serum lysozyme activity tended to be higher for fish fed diets supplemented with
nucleotide, while extracellular superoxide anion production of head kidney macrophages from fish fed
diets with 1% nucleotide was significantly (P< 0.05) increased, although no significant differences were
observed between fish fed 0.5% nucleotide diet and the basal diet.