Physical masculization and growth performance of Oreochromis niloticus placed on 17α-methyltestosterone treated diet
Precocious reproduction of Nile tilapia still remains an impediment to its commercial culture. Various techniques have been used to solve this, including the culture of all male populations. The use of 17 α-methyl testosterone for sex reversal has been practiced but the effective dosage to maximize this technology is yet to be established for Oreochromis niloticus. This study was therefore conducted to evaluate the effect of different doses of 17 α-methyl testosterone (MT) on the sex reversal and growth performance of O. niloticus. Nile tilapia brood stocks with average weight of 220±7g were appropriately paired in happas. After two weeks, fertilized eggs were taken from the mouth of the female and hatched in jars. 300 fry were randomly stocked in 15 plastic aquarium tanks at a density of 33fish/m2, forming five treatments with three replicates. Fry feed of 45% crude protein was treated with different levels of 17 α-methyl testosterone to form five treatments (MT0, MT1, MT2, MT3, MT4 with 0mg, 20mg, 40mg, 60mg, and 80mg of MT/kg of feed respectively) fed to the tilapia fry after yolk absorption for 28 days. Percentage Specific Growth Rate (SGR), Mean Weight Gain (MWG), survival rates, and water quality were measured. Sex determination through histological examination was done following the gonadal squash method. Descriptive analysis and ANOVA were used to analyze the data collected. Results revealed that treatment MT3 had the highest SGR) of 7.57±0.3%, followed in descending order by treatments MT1, MT2, MT0 (control), and (MT4) with values 7.46±0.3%, 7.31%±0.2%, 7.28%±0.2% and 7.08%±0.5% respectively. The MWG (%) showed that treatment MT3 had the highest value of 11.0±13.1% while treatments MT4 had the least MWG of 8.2±21.5%, MT0, MT1 and MT2 had 9.1%±2.8, 10.2±9.9% and 9.3±4.3% respectively. Treatment MT3 also had the best survival rate percentage of 86.7±5.7% while the least was recorded in MT4 with value of 70%±5.0. Treatment MT3 with 60mg/kg of MT diet was the most efficient in sex reversal, resulting in 80±3.34% males, 20.0±7.8% intersex and no female, while MT4, MT1 MT2 and MT0 had 60±6.2% 50±4.2%, 50±6.9%, 25±2.9% respectively. Results showed that 17 α-methyl testosterone had a significant effect on the sex ratio of the fish. 60mg/Kg of MT in feed was the most effective of all the doses tested.
Keywords: Sex reversal, Monosex, Precocious reproduction, Oreochromis niloticus