Juvenile channel catfish, Ictalurus punctatus, were fed diets supplemented with yeast or yeast subcomponents (YYS) as commercial preparations of beta-glucan (MacroGard (R) and Betagard A (R)), mannan oligosaccharide (Bio-Mos (R) Aqua Grade), or whole-cell Saccharomyces cerevisiae (Levucell SB20 (R) at the manufacturers recommended levels. Fish were fed experimental diets for 1 or 2 weeks prior to disease challenge (pre-challenge feeding periods) and sampled at the end of each feeding period to measure haematological and immune parameters and to determine the effects of dietary YYS on resistance to Edwardsiella ictaluri, the causative agent of enteric septicaemia disease (ESC). Feeding of experimental diets continued for 3 weeks post-challenge. In channel catfish fed diets supplemented with MacroGard (R) Betagard A (R) or Levucell SB20 (R) survival in the 1 week pre-challenge feeding group and antibody titres in the 2 week feeding group were significantly higher post-E. ictaluri challenge in relation to catfish fed with the control diet. In fish fed these same three diets, survival to ESC was significantly higher after 1 week vs. 2 weeks feeding, while the antibody response was significantly higher after 2 weeks vs. 1 week. Lysozyme activity was also higher in the 1 week feeding group, but the increased activity was unrelated to diet. Feeding YYS-supplemented diets for a shorter duration of 1 week prior to challenge may prove beneficial in increasing resistance to ESC in channel catfish. However, we cannot discount that feeding YYS diets during the recovery period may have contributed to glucan overload and reduced survival in the 2 week feeding group.
