Abstract
Synthetic androgen, 17 α-methyl testosterone (MT), is widely used to reverse the sex in order to get all male progeny in Nile
tilapia (Oreochromis niloticus). Present project was therefore planned to monitor the effect of different dose rates of MT i.e.
50, 60, 70 and 80 mg/ kg of feed on the sex reversal, growth increments and meat quality (proximate body composition and
organo-leptic qualities) of Nile tilapia. MT was administrated orally by using 40% crude protein feed to tilapia hatchling in
glass aquaria for 25 days. Then the hatchling was shifted to earthen ponds in order to monitor its growth for 20 fortnights.
Organic manure and 40% CP was used in ponds at 1:1. After the experiment the sex ratio was assessed by gonad squash
method. Growth performance was evaluated by recording morpho-metric characteristics i.e. body weight and total body
length. Meat quality of the experimented fish was determined by proximate body composition following the standard method
of AOAC and organo-leptic evaluation. Important water quality parameters were also recorded throughout the experiment.
All the treatments MT treatments showed a highly significantly higher male progeny than control which showed normal sex
ratio 1:1 (male: female). The dose of 70 mg MT/ kg of feed yielded maximum male proportion (98%) with no female and
fewer intersexes (2%). Among the other MT treatments, dose rate of 50 mg resulted in minimum male proportion (80 %),
highest female (13.8%) and highest intersexes (6.2%). Dose rate of 60 and 80 mg resulted in 89 and 90.7% male population.
Dose rate of 70 mg also gave significantly maximum fish production i.e. 3342 kg/ ha./year, 1.6 times greater than control.
Control treatment showed maximum body protein contents i.e. 15.69%, significantly different from all other treatments. 70
mg treatment showed a highly significant difference with respect to total body fats contents having maximum value of 3.52%
fat. The lowest bone: meat ratio was exhibited by dose rate of 70 mg i.e. 1:27. All treatments showed a non significant
difference in respect of different organo-leptic qualities of meat i.e. colour, texture, softness and overall acceptability except
flavour, in which they differed significantly. Water quality parameters recorded during the entire period remained under
favourable limits for fish culture. Regression studies revealed a highly significant dependence of fish growth on water
temperature and planktonic biomass.
