Tilapia Sex Reversal, the technology for producing all-male tilapia, has revolutionized the fanning of the fish world wide.
The technology which is regarded as a milestone in global aquaculture is widely applied in the Philippines and other countries like Israel, Thailand, and the United States. More than 50 percent of the Nile tilapia produced in ponds and cages in the Philippines have been sex-reversed.
The technology is based on the theory that the development of the sex organ (testis for male and ovary for female) in the fish can be artificially influenced by feeding of a synthetic sex hormone (methyltestosterone for male and estrone for female) during the “sexless period” of the young. Hormonal or induced sex reversal was first demonstrated in the 1950s by T. K-O. Yamamoto of Japan in the medaka, an aquarium fish.
Artificial sex reversal is considered the most effective, efficient and economical method for solving the major drawback of growing tilapias to market-size caused by unwanted reproduction. With mix-sex (male and female) stocks, the fish matures early and breeds frequently resulting in stunted growth due to overpopulation in ponds. By growing all-male tilapia produced through hand-sexing (manual separation of sexes), hybridization (crossbreeding of two appropriate species) or sex reversal, the yield of large-sized tilapias is significantly increased by 30 percent to 50 percent because of the faster-growing males compared to females and the control of reproduction.
In the Philippines, the sex reversal technology was first experimentally applied to the Mozambique tilapia and then to the Nile tilapia with spectacular success in the 1970s at the Freshwater Aquaculture Center of the Central Luzon State University in Munoz, Nueva Ecija. It was first commercially applied at the Tilapia Hatchery and Cage Culture Project of the Meralco Foundation in Jala-Jala, Rizal in the 1980s with the technical assistance of Aquatic Biosystems.
Since its development as a “breakthrough,” the application of tilapia sex reversal has undergone a number of innovations. While at first it was believed that the treatment of fry could only be done under a shade, it is now being done in outdoor tanks and ponds. Although anyone with the proper know-how and equipment can prepare the hormone-feed and apply it, there is a tilapia sex reversal feed now available in the market for those who find it more convenient and practical.
Applying the sex reversal feed method with a success rate of at least 95 percent requires the production of the right age of the fry for treatment, preparation of the hormone feed or its procurement, and the proper application of the treatment. It is important that the fry to be treated be not more than 3 days from the time they are released by the mouth brooding females in breeding ponds when the fry are about 10 days old from hatching of the eggs and 9 millimeters to 11 millimeters in total length. The fry to be treated also need to be stocked in the hapas, tanks or ponds at the proper densities and fed at recommended feeding rates for good growth and survival, and effective sex reversal.
The commercial tilapia sex reversal feed (SR Premix) is available from its exclusive manufacturer and distributor, Aquatic Biosystems (aquabios@yahoo.com).
By Dr. Rafael D. Guerrero III
