SUMMARY Methylene blue, Pot, perinanganate and copper sulphate displayed a high efficacy in treatment of fish ectoprotozoal infections by Chilodonella hexosticha. The infected Tilapia nilotica fish showed a significant increase in serum GOT, GPT and alkaline phosphatase activities as well as phosphorus level whereas albumin, calcium and cholesterol levels were decreased. The previous changes in serum constituents were completely subsided one week post-treatment. It is concluded that methylene blue, pot. perinanganate and copper sulphate have a high efficacy in Tilapia nilotica ectoparasites. Moreover, the observed adverse-effects on serum constituents retumed to their control levels, one week post-treatment.