Haematological and immunological changes in channel catfish stressed by handling and transport

Handling of fishes in the field or in the laboratory is frequently characterized by increased susceptibility to disease thought to be mediated by immunologic suppression. In order to ascertain if such immunologic suppression occurs after stress, we developed a laboratory model for the induction of acute handling and transport stress that could reproducibly effect both haematological and immunological changes in channel catfish. Eighteen hours after the induction of stress there was a marked lymphopenia which appeared to be the result of a reduction in the number of both T and B lymphocytes in the circulation. There was also the expected neutrophilia with increases of up to 30% of the circulating leucocytes. Studies on the in vitro immunological function of the remaining circulating lymphocytes demonstrated that cells from stressed fish could no longer respond to the mitogens LPS and ConA, nor could they undergo primary anti‐hapten antibody responses to either T‐dependent or T‐independent antigens. These losses of in vitro function could not be attributed to the presence of stress‐induced suppressor cells or to a loss or diminution of accessory cell function.