UNLESS you are raising them, you may have already eaten transsexual tilapia. Those that you buy from the commercial market are grown using the sex reversal technology, which the Philippines has pioneered.
As much as 90% of the tilapia cultured in the country is sex-reversed, according to Dr. Rafael D. Guerrero III. “At least 50% of the tilapia produced in the United States, Canada, Israel, the Caribbean and Asia is sex-reversed,” he points out.
Dr. Guerrero is an Academician of the National Academy of Science and Technology. He has over 40 years of experience in aquaculture with emphasis on tilapia culture as researcher, professor and consultant. He served as the executive director of the Philippine Council for Aquatic and Marine Research and Development.
As the “Father of Tilapia Sex Reversal,” he has received several citations from different award giving bodies. In 2004, he was conferred the Mgr. Jan D.F. Heine Memorial Award by the International Tilapia Foundation.
“Tilapias are early-maturing and prolific breeders,” he says. “The fishes become sexually mature at two to three months and females are capable of spawning a hundred to a few hundred eggs, depending on size.”
Sexes are differentiated externally by examining the structure behind the anus. The male has only one opening in the structure while the female has two openings. Male tilapias grow faster than females.
Tilapia’s high production rate oftentimes results in overcrowded ponds and stunted fish. In the past, hand sexing — separating males from females — was the solution being used. But doing so takes times. That’s why the sex reversal technology was developed by Dr. Guerrero.
The sex reversal technology was 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.
Most economical method
According to Dr. Guerrero, 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% to 50% because of the faster-growing males compared to females and the control of reproduction.”
Although anyone with the proper know-how and equipment can prepare the hormone-feed and apply it, there is atilapia 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,” 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.
Safe for consumption
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.”
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?
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.”
Low in cholesterol and fat
Most of the tilapia raised in the Philippines are consumed locally. Filipinos relish tis cotton-like meat and fairly good taste. Both Americans and Europeans are also fond of tilapia since they consider it as “white meat,” a health food low in cholesterol and fat. Also, chefs have a preference for tilapia’s firm meat.
Unfortunately, a study done in the United States has shown that eating tilapia is not good for those with heart problems. “Cardiologists are telling their patients to go home and eat fish, and if the patients are poor, they’re eatingtilapia. And that could translate into a dangerous situation,” said the researchers from the Wake Forest University School of Medicine.
The university study showed that farm-raised tilapia, one of the most highly consumed fish in America, has very low levels of beneficial Omega-3 fatty acid and, perhaps worse, very high levels of Omega-6 fatty acids, researchers claimed.
They said the combination could be a potentially dangerous food source for some patients with heart disease, arthritis, asthma and other allergic and auto-immune diseases that are particularly vulnerable to an “exaggerated inflammatory response.” Inflammation is known to cause damage to blood vessels, the heart, lung and joint tissues, skin, and the digestive tract.
In an article which appeared in the Journal of the American Dietetic Association, the researchers claimed that tilapiahas higher levels of potentially detrimental long-chain Omega-6 fatty acids than 80-percent-lean hamburger, doughnuts and even pork bacon.
So eating tilapia is worse than bacon? That was Dr. Floyd Chilton, a professor of physiology and pharmacology and the director of the Wake Forest Center for Botanical Lipids, told the American media.
“For individuals who are eating fish as a method to control inflammatory diseases such as heart disease, it is clear from these numbers that tilapia is not a good choice,” Dr. Chilton was quoted as saying. “All other nutritional content aside, the inflammatory potential of hamburger and pork bacon is lower than the average serving of farmed tilapia.”
Tilapia vs. bacon
Let’s take a closer look at the comparison. Tilapia has 26 grams of protein while bacon has a measly 0.07 gram. Tilapia’s fat content is three grams compared to 100.76 grams for bacon. In addition, tilapia is an excellent source of phosphorus, niacin, selenium, vitamin B12, and a good source of potassium. Bacon, on the other hand, contains 1,000 milligrams of sodium, 166 milligrams of cholesterol, and enough possible carcinogenic nitrites to make pregnant women think twice.
“Tilapia is not necessarily worse just because it contains less Omega-3 than salmon and more Omega-6 than bacon,” wrote Dr. Eliza Mei Perez Francisco, a nutrition support physician at St. Luke’s Medical Center, in an article. “It still has many nutritional benefits, and cannot be judged solely on its potential to cause inflammation.”
If you take note, the American researchers are focusing on farmed tilapia. “In a fish-farming situation, the fish that you get depends on what they are fed,” explained Dr. Chilton, who headed the study. “We must feed animals the correct foods. Animals become what we feed them, and we become what we eat as well. The food chain is fairly consistent.”
Dr. Guerrero seems to agree. “It is true that farmed tilapia has lower Omega-3 fatty acids than marine fish that feed on natural food (algae) in the ocean compared to tilapia fed in ponds and cages using feeds containing corn,” he explains. “But this applies more in the United States. In the Philippines, we feed our tilapia with rice bran and soybean meal that contain less Omega-6 fatty acids.”
On the controversy which tilapia has created a stir among health buffs, Dr. Guerrero has this answer: “There is still a controversy or disagreement among nutritionists with regard to the right balance of Omega-6 and Omega-3 which we both need in our diet. More studies are needed.”
Meanwhile, Dr. Francisco urged Filipinos not to give up tilapia, particularly those raised in ponds, completely. “Continue to eat fish regularly, at least twice a week, and combine tilapia with Omega-3-rich fish (like tuna, salmon, and mackerel) for a more balanced mix of fats.”
Instead of frying tilapia, she recommended that you grill, boil or steam the tilapia. “This will help you cut down on total fat in the diet.” But if you want to fry or sauté it, use canola or olive oil. Or cook in coconut milk (as in ginataang tilapia).
By the way, unlike other fish, tilapia has very low levels of mercury because it is fast growing- and short-lived fish that mostly eats a vegetarian diet.
