SEXUALLY REVERSED TILAPIA 2 OF 2

Sex Reversal Treatment

The three-week sex reversal treatment of tilapia fry can be done in indoor tanks or outdoor hapas in tanks/ponds. The fry are stocked at densities of 250-1,000 per square meter and fed the hormone-feed that can be prepared by the user or purchased from a commercial supplier.
In the first week of treatment, the fry are stocked at 1,000 per square meter and fed at the rate of 30% of their body weight daily in four feedings given twice at 8 a.m. to 10 a.m. and twice at 2 p.m. to 4 p.m. at two-hour intervals. For 1,000 fry weighing on the average o.ol gram each at the start of the treatment, 3 grams of the hormone-feed are given daily in four feedings (twice in the morning and twice in the afternoon) for 7 days.

In the second week of treatment, the stocking density of the post-fry (18-22 mm in total length) is reduced to 500 per square meter to hasten growth. The feeding rate of 25% of fish total weight daily in four feedings as in the first week is applied. For 1,000 post-fry weighing on the average 0.05 gram each, 12.5 grams of the hormone-feed are given per day in four feedings.
In the third week of treatment, the stocking density of the fingerlings (more than 25 mm in total length is further reduced to 250 per square meter and a feeding rate of 20% of total body weight of the fish is applied. For 1,000 finger-lings weighing 0.1 gram each, the amount of hormone-feed given per day in four feedings is 20 grams.
For fast growth and high survival (70-80%) of the treated fish, good water quality should be maintained by replacing and/or cleaning the clogged-up net enclosures and providing for water change and artificial aeration when necessary. If properly applied, the sex reversal treatment can be 98-100% effective.
Culture of Treated Fish
Following the sex reversal treatment, the finger-lings weighing on the average 0.5 gram can be stocked in nursery units for further rearing to larger sizes for cage/pen culture or stocked in grow-out ponds that should have no “wild fish.” The use of sex-reversed fingerlings allows for stocking rates that are higher than with mixed-sex fish. The usual preparations and management can be applied.

For fast growth and high survival (70-80%) of the treated fish, good water quality should be maintained.
How artificial sex reversal works?
The theory behind artificial sex reversal is that the feeding of the right dosage of a synthetic male sex hormone (i.e. methyltestoster-one) at the right time of fry development known as the sex differentiation stage and for the right duration (three weeks) can result in the conversion of would-be genetic females into functional males. In other words, sex-reversed fish have the sex chromosomes of the female (XX) but the sex organ of the male (testis). Genetic males (XY) are not altered. The process is not reversible.
With all-male cultured tilapia, reproduction of the fish is controlled thus avoiding over Population; faster growth of the fish is achieved because of the male superiority and high yields of large-sized fish can be attained.
How to prepare the hormone-feed?
The hormone-feed for artificial sex reversal of tilapia can be prepared with the following procedure:

1. Dissolve 3 grams of methyltestosterone (in powder form) obtained from a supplier (e.g., Argent Chemicals) in 2 liters of 95% ethanol (ethyl alcohol) to prepare the stock solution.
2. Thoroughly mix 200 cubic centimeters (cc) of the stock solution with 1 kilogram of the fry feed (mash).
3. Spread the mixture on a clean dry surface indoors and allow the alcohol to evaporate.
4. When the mixture is dry, place it in a resealable container.
5. The hormone-feed is now ready for use within the next 30 days.

Note: Methyltestosterone is a restricted drug used for human medicine and should be used with caution and responsibility. A commercial tilapia sex reversal premix feed is locally available from Aquatic Biosystems.
Is the application of artificial sex reversal economical?
It only costs less than 2 centavos to produce a fingerling treated for artificial sex reversal. Sex-reversed fingerlings are sold 5 to lo centavos more per than non-treated ones.
Is the use of methyltestosterone safe for tilapia consumers?
Studies have shown that 5 days from withdrawal of the hormone-feed, the levels of the male sex hormone in the treated fish return to normal indicating that no residues are present. With several months from the time of withdrawal of hormone-feed to the time of consumption of the treated fish, consumers are assured that the fish are absolutely safe for eating.
Part 1

For more information, contact:
Dr. Rafael D. Guererro III (PCAMRD)
Phone: (049) 536-1582/5578
Web: www.pcamrd.dost.gov.ph
Hormone-Feed Formulation Supplier:
Aquatic Biosystems
Tel. (63) 049-568-0073,
Mobile Phone: 0917-8016641
Email: aquabios@laguna.net
Web: http://cal-nu.laguna.net/aquabios
source: Marid Digest