Effect of Diet on the Immune Response of Rainbow Trout (Salmo gairdneri)

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Abstract
To compare the effect of diet on the immune response of rainbow trout (Salmo gairdneri), we maintained fish on either a commercial feed or a laboratory prepared (control) diet for 12–16 wk before antigenic exposure. The immune response to two antigens, sheep red blood cells (SRBC) and Yersinia ruckeri, was assessed. Both T-cell (migration inhibition factor) and B-cell (plaque-forming cell) responses to SRBC were measured. The plaque-forming cell response and the humoral (serum antibody) responses to Y. ruckeri were assayed. In addition, the phagocytic ability of peritoneal macrophages was assessed as a nonspecific resistance factor. We found that fish maintained on the commercial diet had a significantly lower immune response when compared with fish fed the control diet, although all fish appeared healthy and suffered no mortalities throughout the experiment. We indicate the importance of considering the effects of diet on immunity and disease resistance in future feed formulations.