RESUMEN
Influence of time of antigen administration on antibody response to bovine serum albumin in the fish, O. mossambicus and variations in serum antibody titre during a 24 hr cycle are reported. Significant variations were observed in magnitude of antibody response in groups of fishes immunized at different times of the day. Magnitude of the response was maximal in fish immunized at 16 hr and minimal in those immunized at 4 hr. Serum antibody titres in a 24 hr study also varied markedly with general elevation during day time, reaching the maximum at 12 hr and depression during night with the lowest titre at 4 hr. These results can be positively correlated to diel variation in number of leucocytes or proportion of lymphocytes which in turn is possibly correlated (negatively) to the periodicity in plasma corticosteroid level.