Citrus by-product is a potential alternative to replace synthetic ascorbic acid in the diet of juvenile red seabream, Pagrus major

This study evaluated the effects of replacing synthetic L-ascorbic acid (AA) in diet with citrus by-product (CBP) on growth, feed utilization, innate immunity and disease resistance of red seabream, Pagrus major. Three experimental diets were formulated incorporating 30, 90, and 300 mg/kg of AA (AA30, AA90, and AA300, respectively) and another three diets were formulated, replacing those levels with CBP (CBP30, CBP90, and CBP300, respectively). The analyzed AA contents in AA30, AA90, AA300, CBP30, CBP90, and CBP300 diets were 55.9, 100.9, 207.6, 67.6, 117.1, and 300.7 mg/kg, respectively. Triplicate groups of fish (initial body weight, 30.5 ± 0.4 g) were fed an experimental diet for 12 weeks. Growth performance, feed utilization and survival did not significantly differ among treatments. Bone collagen content was not affected by AA source or level. The AA content in the liver significantly increased with increasing dietary AA levels but was not affected by increasing CBP levels. In comparison to AA supplementation at 30 mg/kg, AA levels above 90 mg/kg significantly increased lysozyme, superoxide dismutase and nitro-blue tetrazolium activities. Myeloperoxidase and antiprotease activities were not significantly different among treatments. After 16 days of the challenge test against Streptococcus iniae, survival percentages were 44%, 58%, 53%, 33%, 55%, and 72% in AA30, AA90, AA300, CBP30, CBP90, and CBP300 groups, respectively. The results indicated that CBP is a viable alternative AA source to replace synthetic AA in the diet of red seabream.