Changes in immunoglobulin producing cells in response to gonadal maturation in rainbow trout

Changes in the number of immunoglobulin producing cells (IPC), immunoglobulin M (IgM) levels and leukocyte counts were investigated in rainbow trout reared under constant water temperature with special reference to gonadal maturation. During the spawning season, leucocytopenia, decreased number of antibody producing cells and low plasma IgM levels were observed. These reductions were apparently correlated with elevations in plasma cortisol (F), testosterone (T) and estradiol-17 beta in female and F, T and 11-ketotestosterone in males. In addition, decreased number of antibody producing cells in the skin lymphocytes and low mucus IgM levels were observed during the spawning season. These results suggest that endocrine changes related to gonadal maturation cause overall suppression of immune functions.