EFFECT OF FEEDING 17a- METHYLTESTOSTERONE AND WITHDRAWAL ON FEED UTILIZATION AND GROWTH OF NILE TILAPIA (OREOCHROMIS NILOTICUS L.) FINGERLINGS

Fingerlings Nile tilapia (Oreochromis niloticus) were orally adminis‌tered 17a -methyltestosterone (MT.). Fish received 0, 2, 5, or 8 mg MT/Kg diet for 20 weeks (phase-1) followed by 8 weeks withdrawal peri‌od (Phase II). At the end of Phase! -1, fish received 2mg MT/Kg diet (best treatment) exhibited significantly higher (P <0.05) weight gain over the control by 44.5%. Likewise, food conversion ratio (FCR),protein efficeincy ratio (PER), and productive protein value (PPV) among group receiving 2mg MT/Kg diet were significantly better than the control (2.82 versus 3.40, 1.14 versus 0.94 and 18.15 versus 14.98 respec‌tively). The anabolic property of dietary steroids became more visible af‌ter 10 weeks. Increasing the dietary concentration of MT more than 2mg / Kg diet reduced fish growth and feed utilization efficiency, but not be‌low the level of control. The results of the present study showed increase in moisture, protein, fat and ash deposition in fish body with the decrease of MT lev‌els in the diet. In other words, the niltrients were more retentive in fish body with lower doses than with higher doses of dietary MT.Fish group received 2mg MT / Kg diet had greater retention values than of those the control group by 47.7%, 44.9%, 20.8% and 35.1% for moisture, protein, fat and ash respectively. Viscro-somatic indices (VSI) of the MT-treated fish were slightly but not significantly (P>0.05) higher than those of the control. The go-nado-somatic indices were significantly (P<0.05) higher in the MT-treated fish than the control.