A study of the haematological and serological parameters (erythrocyte and leucocyte numbers, haematocrit, haemoglobin, blood group and genotype) is reported for four freshwater, pond-cultured catfish groups from the fish farm of the African Regional Aquaculture Centre, Aluu, Port Harcourt, Nigeria. Erythrocyte and leucocyte counts showed intra-species variability, while fish size was found to be negatively correlated to haemoglobin concentration and haematocrit values; these are significant at P = 0.05 level. The serological results obtained were found to be similar to the pattern in humans.