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Optimization of Dose of Methyl Testosterone (mt) Hormone for Sex Reversal in Tilapia (oreochromis Niloticus L.)

M. Abdur Rouf
Department of Fisheries Biology and Genetics, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

M. Rafiqul Islam Sarder
Department of Fisheries Biology and Genetics, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Farhana Rahman
Department of Fisheries Biology and Genetics, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

M. Faridul Islam
Department of Fisheries Biology and Genetics, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Abstract/ Executive Summary:

This paper describes the optimization of dose of methyltestosterone (MT) hormone for masculinization of tilapia (Oreochromis nilolicus). Five treatments (i.e. T₁, T₂, T₃, T₄ and T₅) with different doses such as 0, 40, 50, 60 and 65 mg of MT hormone were mixed with per kg of feed for each treatment and fed the fry four times a day up Lo satiation for a period of 30 days. The stocking density was maintained 10 spawn/liter of waler. The growth of fry at different treatments was recorded weekly and mortality was recorded daily. AL the end of hormone feeding the fry were reared in hapas fixed in ponds for another 70 days and at the 100^th day the fish were sexed by the gonad squashing and aceto-carmine staining method. The analysis of growth data did not show any significant variation in length and weight of fish among the different treatments. High mortality of fry ranging 66% to 81.6% was observed in different treatments and highest mortality was observed during the first twelve days of the experiment. The sex ratio analysis showed that T₂ (40 mg/kg) and T₅, (65 mg/kg) produced 93.33% of sex reversed male and T₃ (50 mg/kg) and T₄ (60 mg/kg) produced 96.66% sex reversed male, and these ratios were significantly (p<0.05) different from 1:1 male: female sex ratio. The control, T₁ (0 mg/kg) contained 43.33% male progeny. From these results it is suggested that either 50 mg/kg or 60 mg/kg of MT with a feeding period of 30 days could be considered as an optimum dose for masculinization of tilapia (0. niloticus).

Keywords: Masculinization, Methyltestosterone, Tilapia

Location: Faculty of Fisheries, Bangladesh Agricultural University.

Start Date:

End Date:

Program Area: Variety and Species

Commodity: Tilapia

Objectives:

To optimize the dose and duration of MT for the sex reversal of 0. niloticus.

Methodology:

Experiment site: The experiment was conducted in the hatchery of Fisheries Biology and Genetics Department, Faculty of Fisheries, Bangladesh Agricultural University (BAU), Mymensingh. Three day-old spawns of tilapia (0. niloticus) were collected from a private tilapia hatchery named Reliance Aqua Farm Ltd., Bailore, Trishal, Mymensingh. Design of the experiment: The experiment was comprised of five treatments (T₁_, T₂, T₃, T₄ and T₅) of different doses (except control which was hormone free) of MT hormone. It was conducted in 5 glass aquaria of ( 45 x 25 x 24) cm³ size each and contained 25 liter of water. 250 spawns were stocked in each aquarium. The average length and weight of spawns were 7.75±0.05 mm and 0.006 g respectively and the stocking density was maintained 10 spawns/liter of water. The spawns were reared for 30 days. Four diets with different doses of MT hormone i.e., 40, 50, 60 and 65 mg/kg were prepared through ethanol evaporation method. To prepare 100 g feed for each treatment, required amount of MT hormone (i.e., 4, 5, 6 and 6.5 mg MT hormone for T2, T₃, T₄ and T₅ respectively) was diluted with 60 ml of alcohol for homogenous mixing with the feed in each treatment. Ground and sieved fish meal was used for preparing the feed. In case of control, required amount of feed was prepared by mixing ethanol only. The prepared feeds were preserved in a refrigerator at 4°C. Feeding and sampling of fry: The spawns were fed with hormone mixed feeds 4 times (from 7:00 am to 07:00 pmwith four hour interval) a day up to satiation. The water of each aquarium was exchanged by 75% of the volume with fresh water once a day in the morning to avoid water quality deterioration due to decomposition of left over feed and feces of the spawns. In addition, the faecal out-put and wastes of feed were removed from the aquarium by siphoning at 9:00 am and 5:00 pm daily. Additional oxygen was provided to aquarium through aeration for 22 hrs everyday from two aerators and was stopped for half an hour each time during feeding. The fish were sampled at weekly interval to determine the increase in their size (length and weight). Sampling was done in the early morning when the fish stomach was about to be empty to avoid the biasness of weight due to the presence of excessive feed. Ten fry were randomly collected from each aquarium and the weight of all fry was taken together due to their small size in an analytical balance. The length (mm) was measured by placing the fish on a petri dish having a 1 mm graph paper underneath it. Mortality of the fry was recorded daily. The experiment was continued for 30 days and at the end of the experiment the fish were transferred to hapas fixed in a pond and reared them with the normal feed until being sexed. The hormone feeding was terminated at the 30th day of experiment but the fish were reared for another 70 days with normal feed for proper sexing. At the age of 100 days, the final growth and mortality(%) of fish were estimated. Water pH and temperature in each aquarium were estimated at seven days interval. Fish sexing: The fish were sexed by gonad squashing and aceto-carmine starnrng method. The fish was killed and the viscera was removed to reveal the two thread like gonads lying along the upper surface of the body cavity on either side of the kidney. The gonads were removed and placed on a clean glass slide. A few drops of aceto-carmine stain were added and the gonads were squashed with a cover slip. The sex of the fish was identified by examining the slides under a microscope. Statistical analysis: The length gain (mm), weight gain (g) and mortality (%) of fish of different treatments were tested using one way analysis of variance (ANOVA) followed by DMRT to identify differences among the means. This statistical analysis was performed with the aid of the computer software SPSS and MS excel programs.

Source of Information: Bangladesh J. Fish. Res., 12 (2), 2008: 135-142

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

It was found that, 50 mg/kg and 60 mg/kg doses of MT produced the highest percentage (96.66%) of male sex, therefore either 50 mg/kg or 60 mg/kg of MT could be recommended as optimal dose for masculinization of tilapia in hatcheries.

Knowledge Management: Journal