Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2008
Publication Date: 5/1/2009
Citation: Lim, C.E., Aksoy, M., Li, M.H., Welker, T.L., Klesius, P.H. 2009. Growth performance, immune response and resistance to Streptococcus iniae of Nile tilapia fed diets containing various levels of vitamins C and E. Journal of the World Aquaculture Society. 41: 35-48.
Interpretive Summary: Vitamins C (L-ascorbic acid) and E (a-tocopherol), which are very important antioxidants, are among the most important nutrients that influence the immune system and disease resistance of animals, including fish. These vitamins provide cellular defense against reactive oxygen species which damage biological membranes. Results of earlier studies with some fish species other than tilapia demonstrated more pronounced deficiency signs in fish depleted in both vitamins and some compensatory effects when one of the vitamins was fed at a high dose. Thus, this study was conducted to evaluate the effect of dietary levels of vitamins C and E, and their interaction on growth performance, liver vitamin storage, hematology, immune response and resistance of Nile tilapia (Oreochromis niloticus) to Streptoccocus iniae challenge. Results of the present study showed that supplementation of 100 mg vitamin C/kg was needed for optimum growth performance and feed utilization efficiency of juvenile Nile tilapia. Vitamin E present in the basal diet (23 mg/kg) was sufficient for good growth. However, supplementation of 50 mg/kg was required for good survival. The sparing effect of vitamin E on survival was observed in fish fed the vitamin C-unsupplemented diets. Liver storage of vitamins C and E was directly related to dietary levels of each vitamin. Dietary vitamin E level had no effect on liver vitamin C content, but increasing dietary vitamin C, especially at 2,000 mg/kg, increased liver vitamin E content. Supplementation of both vitamins was required for optimum hematological indices and prevention of macrocytic anemia. The effect of dietary levels of these vitamins on immune function and the susceptibility to S. iniae was inconclusive. Nevertheless, we observed that excessive levels of vitamin C or E appeared to be of little or no benefit in improving the immune response, except for an increase in total immunoglobulin in fish fed 2,000-mg vitamin C diets. Supplementation of vitamins C and E at levels necessary to sustain good growth and survival (100 and 50 mg/kg diet, respectively) appeared adequate to sustain a normal immune response and resistance of Nile tilapia to S. iniae challenge. Additional studies to further determine the roles of vitamins C and E in immune response and resistance to infectious diseases are recommended.
Technical Abstract: The effect of dietary levels of vitamin C (0, 100, 2,000 mg/kg), E (0, 50, 500 mg/kg), and their interaction on growth performance, immune response and resistance of Nile tilapia, Oreochromis niloticus to Sterptococcus iniae challenge were evaluated. Each diet was fed to Nile tilapia in triplicate aquaria to apparent satiation twice daily for 12 weeks. Supplementation of vitamin C at 100 mg/kg to the basal diet containing 10.5 mg/kg was sufficient for good growth and feed efficiency. The amount of vitamin E contained in the basal diet (23.1 mg/kg) was sufficient to promote good growth and feed efficiency, but supplementation of 50 mg vitamin E/kg was necessary for good survival. Liver storage of vitamins C and E increased with increasing dietary levels of the corresponding vitamin. Dietary vitamin E levels had no effect on liver vitamin C content, but increasing dietary vitamin C increased liver vitamin E. Except the significant increased in mean corpuscular volume (MCV) in fish fed vitamin E-unsupplemented diets, hematological parameters were not affected by dietary levels of vitamin E. Significantly lower red blood cell count and hemoglobin, and higher MCV) were observed in fish fed the vitamin C-unsupplemented diets. Serum protein and antibody titer were not affected by treatments. Total immunoglobulin and lysozyme activity significantly increased and decreased, respectively in fish fed the 2000 mg/kg vitamin C-diets. Supplementation of vitamin E at 500 mg/kg diet significantly decreased serum alternative complement. Dietary levels of vitamin C had no effect on mortality following Streptococcus iniae challenge, but mortality significantly decreased in fish fed vitamin E-supplemented diets.