By Henrylito D. Tacio
It was in 1950 when Deogracias Villadolid of the Philippine Fisheries Commission brought some species of Tilapia mossambica from Thailand into the country. Although there were no studies made on its management, the fish was introduced in some ponds. As tilapia is a prolific fish, the result was an overcrowded pond.
Many growers considered tilapia as nuisance because it competed for the food of bangus (milkfish), which at that time was considerably more profitable than tilapia. As a result, tilapia vanished into oblivion.
But in 1972, a new tilapia species — Nile tilapia (Oreochromis niloticus) — was again introduced. It caught the attention of the Filipinos as it had better features particularly its whiter color, bigger size, and faster growth.
Today, the Philippines is “now one of leading producers of tilapia in the world,” reports Dr. Rafael D. Guerrero III, an Academician of the National Academy of Science and Technology who popularized tilapia raising in the country today.
In 2013, the Philippines was the fourth largest producer of tilapia in the world with a total production of 316.536 metric tons valued at US$669.8 million. Eighty-five percent of the production was from aquaculture and 15% from inland water fishing.
As a world leader, the Philippines has also set the pace for the use of several technological innovations for tilapia. One of these is the sex reversal technology (SRT). “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,” Dr. Guerrero says.
Dr. 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.
As much as 90% of the tilapia cultured in the country is sex-reversed. “At least 50% of the tilapia produced in the United States, Canada, Israel, the Caribbean and Asia is sex-reversed,” he points out.
Sex reversal technology
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 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,” Dr. 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 (SRT-95) 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,” Dr. 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 9 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,” Dr. Guerrero says.
Because of innovation, there is now a much better commercial SRT feed and it’s called SR Premix. “From SRT-95 which was a single use feed for treating 4,000 fry with at least 95% male percentage of treated fish with proper use, we developed a sex reversal premix which can be mixed at one kilogram of the Premix with 9 kilograms of the fry feed to produce 10 kilograms of SRT-99 for treating 40,000 fry,” Dr. Guerrero says.
The SR Premix, he says, is easier and cheaper to transport. SRT-99 is an improvement over SRT-95 because it is capable of producing up to 99-100% male fry with proper use.
Aquatic Biosystems, a consultancy and marketing firm based in Bay, Laguna, is the exclusive manufacturer and distributor of the SR Premix. It is selling SRT 99 at only P400/kg for treating 40,000 tilapia fry in three weeks.
Safe to eat
But the question is: are sex-reversed tilapia safe to eat?
The synthetic sex hormone used in sex reversal technology is 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 Dr. Guerrero, the oral treatment with methyltestosterone in tilapia is only for 3-4 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 3-4 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.”
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? Dr. 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. “Methyl testosterone, which is for maleness, is therefore not in question,” Dr. Guerrero says.
The use of methyl testosterone 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.”
Food fish
In the Philippines, tilapia ranks as the second most important farmed fish and is considered the “people’s fish” because of its stable market prices and reliable supplies. In fact, most of the tilapia raised in the country are consumed locally.
The popularity of tilapia as a food fish is not exclusive in the country. “In the United States, tilapia has shown the biggest gains in popularity among seafood, and this trend is expected to continue as consumption is projected to increase,” the Journal of the American Dietetic Association reported.
Like Americans, Europeans are also fond of tilapia since they consider it as “white meat,” a health food low in cholesterol and fat. Also, European chefs have a preference for tilapia’s firm meat.
But there’s more to tilapia than just providing food. In the United States, tilapias are stocked in the canals that serve as the drinking water sources for the cities of Phoenix, Mesa, and others. The fish reportedly help purify the water by consuming vegetation and detritus, thus greatly reducing purification costs.
Tilapia also serves as a natural, biological control for most aquatic plant problems. Tilapia consumes floating aquatic plants, such as duckweed watermeal, the most “undesirable” submerged plants, and most forms of algae.
In Thailand, tilapia is becoming the plant control method of choice in reducing, if not eliminating, the use of toxic chemicals and heavy metal-based algaecides. In Kenya, tilapia helps control malaria-causing mosquitoes. Tilapia consumes mosquito larvae, which reduces the numbers of adult females, the disease’s vector.
