Can tilapia in a pond be all-male?
Yes, it’s possible, according to Dr. Rafael D. Guerrero III, an academician at the National Academy of Science and Technology and former executive director of the Philippine Council for Aquatic and Marine Research and Development.
And it could be done through the so-called “sex reversal technique” or SRT. Dr. Guerrero explains: “SRT is the process by which genetic female tilapia fry are converted into functional males through hormone manipulation.”
Although it is not an endemic fish in the country, the Philippines is now one the world’s largest producers of tilapia. In the past, tilapia was considered a nuisance fish because it reproduces so quickly and doesn’t grow to size consumers like.
“Tilapias are early-maturing and prolific breeders,” said Roy C. Alimoane, the director of Mindanao Baptist Rural Life Center, a non-government organization based in Kinuskusan, Davao del Sur. “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, Alimoane claims, 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 only solution being used. But doing so takes times.
That’s why Dr. Guerrero developed SRT. “With mix-sex (male and female) stocks, the fish matures early and breeds frequently resulting in stunted growth due to overpopulation in ponds,” he 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.”
In his study, he used a tilapia sex reversal feed – called SR Premix – which he himself formulated. For his effort, Dr. Guerrero 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.
Today, more than 20 countries around the world are applying the technology commercially.
But instead of using the commercial methyltestosterone (a man-made form of testosterone), pollen from pine trees may do the same trick, according to a study of the Central Luzon State University (CLSU).
“The use of pine pollen in its unprocessed condition enables the change of sex of young fishes used for breeding, turning in 84.59-90.46% males,” said Dr. Ravelina R. Velasca, of CLSU’s Freshwater Aquaculture Center, who headed the study.
Unprocessed condition means the pollen still has a protective cover.
“The use of pine pollen technology in tilapia sex change eliminates health hazards associated with all-male tilapia production,” she added. “It is an environment-friendly approach and could be an alternative to the use of high-priced standard hormone in sex change.”
One good thing about pine pollen technology is that it does not cause deposit of harmful chemicals onto the soil of the pond, which is common in using the standard sex hormone.
“Using the natural product contributes to improving management and standard practices of tilapia culture,” Dr. Velasca wrote in a report published by Bridge, a compilation of success stories collected by the Department of Science and Technology (DOST).
Pine pollen are the male part of the pine tree. A raw pine pollen, it has been discovered, contains the richest seedbed of male hormone, the testosterone derived from plants. “The male and the female reproductive organs are found in the same tree,” Dr. Velasca said.
Pine pollen is easily absorbed by tilapia when taken in powder or in liquid form dissolved in alcohol.
In the CLSU study, the young tilapia fingerlings with no identified sex is fed with different concentrations of pine pollen dissolved in alcohol for 28 days. “For example, 40 milligrams of pine pollen are added and soaked with 62.5 millimeters of alcohol. After seven days of soaking, the filtered liquid is added to 125 grams of commercial feed, fry mash,” Dr. Velasca said.
The feed with the pine pollen solution is air dried and fed to the young fish for 28 days. The feed with pine pollen solution is give 6-8 times per day. After the 28th day, the fish fed with pine pollen solution is transferred to a bigger area and allowed to grow bigger.
“We check the number of males by visually looking at the hole in the belly,” Dr. Velasca said. “In cases it is hard to identify the sex by just looking at the belly, we cut the belly and check the reproductive organ under the microscope.”
But are these tilapia given pine pollen solution safe to eat?
Dr. Guerrero said 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 assured, “there are no residuals left in the system of the fish after 92 hours. Since the fry are grown for at least 3-4 months for market and human consumption, it is very safe. There can, therefore, be no side effects if there is no synthetic hormone left in the systems of the fish.”
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,” Dr. Guerrero said.
If synthetic sex hormone is safe to eat after 3-4 months, how much more for the natural pine tree pollen?
