The use of steroid-treated feeds as 17 a-methyltestosterone for the production of all-male
populations is widespread in tilapia aquaculture. The aim of the present study was to investigate the
misuse effects of methyltestosterone on monosex farmed Nile tilapia, Oreochromis niloticus by evaluation
of hematological and biochemical values. The fishes were obtained from four localities
(Assiut as a control, Beheira, Alexandria and Kafr el-Sheikh: three farms from each governorate
as farmed monosex produced using methyltestosterone). The total erythrocyte count, hemoglobin
rate, hematocrit percentage, mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin
concentration (MCHC), mean corpuscular volume (MCV), white blood cell count, blood platelets,
lymphocyte, monocyte, neutrophils and basophils were determined. The results showed that there
were changes in the erythrocytic series and in the defense white blood cells. Activities of aspartate
aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP), glucose,
cholesterol, total protein, uric acid and creatinine were determined for biochemical study. These
alterations are considered an indication for performance and health of fish in the monosex culture
medium indicating the side effects of overdose induction of MT.