JOURNALOFTHE WORLD AQUACULTURE SOCIETY zyxwvu Vol. zy 29, No. 1 March, 1998 Effect of Dietary Vitamin C on Weight Gain, Tissue Ascorbate Concentration, Stress Response, and Disease Resistance of Channel Catfish zyxw Zctalurus punctatus MENG H. LI, DAVID J. WISE AND EDWIN H. ROBIN SON^ Delta Research and Extension Center, Mississippi State University, P. 0. Box 197, Stoneville, Mississippi 38776 USA Abstract Juvenile channel catfish Ictalurus zyxwvu punctatus (average initial weight, 6.5 &fish) were fed twice daily to apparent satiation with practical-type diets containing 0, 50, 150, or 250 mg supple- mental vitamin C k g from L-ascorbyl-2-polyphosphate for 10 wk under laboratory conditions. At the end of the feeding period, one half of the fish were stressed for 2 h by confinement and both stressed and nonstressed fish were exposed to a virulent strain of Edwardsiella ictaluri. Weight gain and feed conversion efficiency were lower for fish fed the basal diet than those fed diets containing supplemental vitamin C. No differences were observed in weight gain and feed conversion among fish fed diets containing supplemental vitamin C. There were no differences in feed consumption and survival (prior to experimental infection) among treatments. No vitamin C deficiency signs except reduced weight gain were observed in fish fed the basal diet. Serum cortisol concentrations were higher in stressed fish than in non- stressed fish. Dietary vitamin C level had no effect on serum cortisol concentration. As dietary vitamin C increased, ascorbate concentration in serum and liver increased. Confinement stress had no effect on serum and liver ascorbate concentrations. Cumulative mortality of channel catfish 21 d subsequent to experimental infection with E. ictaluri was higher for stressed fish than for nonstressed fish. Regardless of stress or nonstress, overall mortality for fish fed the basal diet was lower than the fish fed diets containing supplemental vitamin C. There were no differences in post-infection antibody levels among treatments or between stressed and nonstressed fish. Results from this study indicate that channel catfish require no more than 50 mgkg dietary vitamin C for normal growth, stress response, and disease re- sistance. Numerous studies have demonstrated that vitamin C is required for various met- abolic functions in channel catfish Zctalurus puncratus (Wilson and Poe zyxwv 1973; Andrews and Murai 1975; Lim and Lovell 1978). Its essentiality for growth of channel catfish has been well documented (Lovell 1973; Andrews and Murai 1975; Lovell and Lim 1978; Robinson 1992). However, its role in disease resistance of channel catfish is not as clear. Megadose levels of vitamin C have been reported to improve immune function in channel catfish (Duve and Lovell 1982; zyxwv I Approved for publication as Journal Article No. J- 9 174 of the Mississippi Agricultural and Forestry Ex- periment Station, Mississippi State University. This project is supported under MIS Project Number 0822. Corresponding author. Li and Lovell 1985; Liu et al. 1989). How- ever, other research indicated that high con- centrations of dietary vitamin C were not beneficial in improving disease resistance of channel catfish (Floyd 1987; Li et al. 1993). Its role in alleviating the effects of stress on channel catfish has not been re- ported; although, feeding high levels of vi- tamin C has been proposed to be beneficial in reducing the effects of certain stressors on fish (Jaffa 1989; Hardie et al. 1991). Stress has been shown to increase the susceptibility of channel catfish (Plumb et al. 1976; Walters and Plumb 1980; Wise et al. 1993) to infectious agents as well as oth- er fishes (Peters et al. 1988; Maule et al. 1989). This response may be related to an elevation in serum cortisol, which has been reported to depress specific and nonspecific Q Copyright by the World Aquaculture Society 1998 1