Effect of different gonadal steroids, hydrocortisone, catecholamines and antithyroidal agent on certain haematological parameters in an air breathing fish, Anabas testudineus (Bloch) commonly known as climbing perch, have been made. The treatment of hydrocortisone, adrenaline, noradrenaline and testosterone brings about a significant increase in RBC counts (polycythemia), Hb content and PCV values as compared to control which were subjected to the treatment of normal saline. Males were more susceptible to the treatment of hydrocortisone, catecholamines than females. Ovocyclin, Duogynon forte and Fertyl treatments bring about anaemia in this fish, i.e. a decrease in RBC number, Hb content and PCV was clearly marked out. Females were more susceptible to Fertyl than males. Lutocyclin failed to bring any significant changes in these blood parameters. Though the treatment of thiouracil could not bring about significant changes in different blood parameters, a tendency of increase in RBC counts, Hb content and PCV was observed. The absolute values for different blood parameters have also been calculated. Possible reason and the mechanism of such changes in different blood parameters are discussed in detail.