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Title: IMMUNE RESPONSE AND RESISTANCE TO STRESS AND EDWARDSIELLA ICTALURI CHALLENGE IN CHANNEL CATFISH, ICTALURUS PUNCTATUS, FED DIETS CONTAINING COMMERCIAL WHOLE-CELL YEAST OR YEAST SUBCOMPONENTS

Author
item Welker, Thomas
item Lim, Chhorn
item Aksoy, Mediha
item Shelby, Richard
item Klesius, Phillip

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2006
Publication Date: 3/1/2007
Citation: Welker, T.L., Lim, C.E., Aksoy, M., Shelby, R.A., Klesius, P.H. 2007. Immune response and resistance to stress and Edwardsiella ictaluri challenge in channel catfish, Ictalurus punctatus, fed diets containing commercial whole-cell yeast or yeast subcomponents. Journal of the World Aquaculture Society. 38(1):24-35.

Interpretive Summary: B-glucans, polysaccharides composed of glucose molecules linked B-1,3 and B-1,6, are most commonly found in the cell walls of yeast and mycelial fungi (Verlhac et al. 1998). The positive health benefits of B-glucans have been studied in many different animals (Raa 2000) with most research focusing on their immune-enhancing properties. However, the efficacy of dietary B-glucan in preventing disease has not been adequately evaluated in channel catfish (Ictalurus punctatus). Dietary supplementation of three commercial B-glucan sources (MacroGard®, Bio-Mos™ Aqua Grade, and Betagard A®) and one commercial whole-cell Saccharomyces cerevisiae preparation (Levucell SB20®) at the manufacturer’s recommended levels was evaluated on the physiological performance of juvenile channel catfish (Ictalurus punctatus). Fish were fed on a dietary regime of 4 weeks of experimental B-glucan diets followed by 2 weeks of control diet, and the effect of dietary B-glucans on hematology, immunity, and growth (at 4 and 6 weeks) and resistance to Edwardsiella ictaluri infection and to low-water stress (at 6 weeks) were examined. B-glucan supplementation in diets did not affect growth, hematology, or immune function. Although survival from E. ictaluri infection was from 5 to 17.5% higher in fish fed B-glucan supplemented diets than in the control group, the increases were not significant. Supplementation of B-glucan in diets also increased stress resistance in channel catfish. Stress resistance in fish fed B-glucan supplemented diets has been reported previously, but thus far, no explanation has been proposed for this effect. The present study and previously published research suggest that dietary B-glucan supplementation does not improve resistance of channel catfish to E. ictaluri. Even though dietary B-glucan can have positive effects on immune function in channel catfish, a corresponding increase in disease resistance is not necessarily conferred. Some fish pathogens, such as E. ictaluri, may not be affected by immune parameters enhanced by B-glucan administration. In addition, high variability exists in the efficacy of dietary B-glucan to boost immunity due to differences in source and dietary concentration of B-glucan and feeding regime. In the current study, feeding of experimental diets for different durations or altering dietary concentrations of the tested B-glucan sources under the same feeding regime may have resulted in enhanced immunity.

Technical Abstract: Dietary supplementation of three commercial B-glucan sources (MacroGard®, Bio-Mos™ Aqua Grade, and Betagard A®) and one commercial whole-cell Saccharomyces cerevisiae preparation (Levucell SB20®) at the manufacturer’s recommended levels was evaluated on the physiological performance of juvenile channel catfish (Ictalurus punctatus). Fish were fed on a dietary regime of 4 weeks of experimental B-glucan diets followed by 2 weeks of control diet. Fish were sampled at the end of each feeding period (4 and 6 weeks) to measure hematological and immune parameters and growth. The effects of dietary B-glucan supplementation on resistance to Edwardsiella ictaluri infection and to low-water stress were examined at the end of the study (6 weeks). B-glucan supplementation in diets did not affect growth performance, hematology, or immune function. Although survival from E. ictaluri infection was from 5 to 17.5% higher in fish fed B-glucan supplemented diets than in the control group, the increases were not significant. Significantly lower levels of cortisol and lactate were observed in Bio-Mos- and Levucell-fed channel catfish, respectively, after low-water stress. Stress reduction in fish fed B-glucan supplemented diets has been reported previously, but thus far, no explanation has been proposed for this effect. The present study and previously published research suggest that dietary B-glucan supplementation does not improve resistance of channel catfish to E. ictaluri. Even though dietary B-glucan can have positive effects on immune function in channel catfish, a corresponding increase in disease resistance is not necessarily conferred. Some fish pathogens, such as E. ictaluri, may not be affected by immune parameters enhanced by B-glucan administration. In addition, high variability exists in the efficacy of dietary B-glucan to boost immunity due to differences in source and dietary concentration of B-glucan and feeding regime. In the current study, feeding of experimental diets for different durations or altering dietary concentrations of the tested B-glucan sources under the same feeding regime may have resulted in enhanced immunity.