The present study. was planned with the aim to determine the optimal dose of oral administration of the androgen 17-α methyl testosterone (MT) for effective sex reversal, of Nile tilapia as well as comparing growth performance and feed utilization, proximate body composition and human food safety of hybrid blue tilapia Oreochromis aures X O. niloticus (T1), normal (T2) and sex reversed Nile tilapia, O. niloticus (T3 , T4 and T5). All treatment groups that received androgen, 17 α methyl testosterone (MT) showed sex reversal in Oreochromis niloticus, with a significantly higher male proportion than female as compared to the control. The dose level of oral administration of 60 mg MT/ kg of feed for 28 days to Oreochromis niloticus resulted in maximum male sex ratio. The treatment groups (T2), that received 60 mg MT for 28 days exhibited the best feed utilization in terms of FCR, PER, PPV% and EU% and in turn growth performance in terms of AFW, AWG, ADG, SGR (%/ day)and survival rates. With regard to hman food safety, tilapias rapidly excrete ingested hormone, with MT levels falling to less than 1% within 100 hours of withdrawing MT. Thus MT was not detectable in adult tilapias, which require a grow-out period of at least five to eight months to reach international marketable size. From the results of the present study it can be concluded that, the use of 60 mg/ kg MT produced statistically higher male sex percentage when done for 28 days post hatch with efficient feed and protein utilization and in turn attaining higher growth performance, survival rates and human safety.
ABSRRACTTilapia fry were produced by hybridization of males of blue tilapia (Oreochromis aureus) with females of Nile tilapia (O. niloticus) and by sex reversal using oral administration of 3 doses (60, 80 and 100 mg/kg diet) of the androgen 17 α-methyltestosterone (MT) for 28 days. Fry were fattening in earthen ponds for 210 days.All treatment groups that received androgen MT (T 3 , T 4 and T 5 ) showed sex reversal with a significantly higher males proportion than females as compared to the control (T 2 ) and hybrid (T 1 ) groups. The treatment group that received 60 mg MT (T 3 ) exhibited the best growth performance parameters (average weight gain, average daily gain and specific growth rate) and feed utilization parameters (feed conversion ratio, protein efficiency ratio, protein production value and energy utilization). The highest percentage of body crude protein; ether extract and ash were detected in T 3 group. With regard to human food safety, tilapias that treated with MT (T 3 , T 4 and T 5 ) rapidly excrete ingested hormone and MT levels falling to lower concentrations than that in both hybrid (T 1 ) and control (T 2 ) groups.
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