Story & photos by Henrylito D. Tacio
Although it is not an endemic fish in the country, the Philippines is now one of the world’s largest producers of tilapia, according to Dr. Rafael D. Guerrero III.
“The Philippines is now the fourth largest producer of tilapia in the world,” says Guerrero, an academician of the National Academy of Science and Technology and former head of the Philippine Council for Aquaculture and Marine Research and Development.
On top of the list are China, Egypt and Indonesia.
In 2013 the Philippines harvested 316.536 metric tons of tilapia valued at $669.8 million. “Eighty-five percent of the production was from aquaculture and 15 percent from inland water fishing,” says the fishery expert who has over 40 years of experience in aquaculture with emphasis on tilapia culture as researcher, professor and consultant.
As much as 90 percent of the tilapia cultured in the country is sex-reversed. “At least 50 percent of the tilapia produced in the United States, Canada, Israel, the Caribbean and Asia is sex-reversed,” he points out.
Guerrero is regarded as the “Father of Tilapia Sex Reversal.” In 2004 he was conferred the Mgr. Jan D. F. Heine Memorial Award by the International Tilapia Foundation for his work.
The sex reversal 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,” Guerrero explains. “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.”
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 (SR Premix) now available in the market for those who find it more convenient and practical.
“Applying the sex reversal feed method 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,” Guerrero says.
It is also important that the fry to be treated be not more than three 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 nine millimeters to 11 millimeters in total length.
“The fry to be treated also need to be stocked in tanks or ponds at the proper densities and fed at recommended feeding rates for good growth and survival, and effective sex reversal,” Guerrero says.
But the question is: are those sex reversed tilapia safe to eat?
But before answering that question, let’s take a closer look at methyltestosterone, a man-made form of testosterone. A naturally occurring sex hormone, testosterone is produced in a man’s testicles. Small amounts of testosterone are also produced in a woman’s ovaries and adrenal system.
“Methyltestosterone is used in men and boys to treat conditions caused by a lack of this hormone, such as delayed puberty or other hormonal imbalances,” notes www.drug.com. “Methyltestosterone is also used in women to treat breast cancer that has spread to other parts of the body.”
According to Guerrero, the oral treatment with methyltestosterone in tilapia is only for three to four weeks during the sexless stage of the fry or what he calls as “the stage of sexual differentiation.”
“After withdrawal of the treatment,” he assures, “there are no residuals left in the system of the fish after 92 hours.” He based this statement from some studies being done.
“Since the fry are grown for at least three to four months for market and human consumption, it is very safe,” he says. “There can, therefore, be no side effects if there is no synthetic hormone left in the systems of the fish.”
But there is also the question of what happens to the metabolites (excreted compounds) of the synthetic hormone, which are eliminated in the environment. Can they affect other organisms and affect people?
Guerrero gives this answer: “Studies have shown that, in the tropics, the high temperature and the effect of sunlight breaks down the metabolites into simpler compounds through biodegradation and photo-oxidation that have no effect on humans.”
Aside from those done in the Philippines, there are also studies conducted in other countries that showed endocrine disruptors from plastics and insecticides in the environment can influence the direction of sex of fishes and possibly humans who consume them towards femaleness or hermaphroditism and not maleness.
“Methyltestosterone, which is for maleness, is therefore not in question,” Guerrero says.
The use of methyltestosterone for tilapia sex reversal is generally accepted throughout the world except in Europe, which has a strict organic (no synthetics) policy. “So far, since its application more than 30 years ago, there is no negative or harmful effect on humans reported.”