“No fish – with the probable exception of the common carp – is more widely cultured than tilapia,” wrote John E. Bardach, John H. Ryther, and William O. McLarney, authors of Aquaculture: The Farming and Husbandry of Freshwater and Marine Organisms.
It was Deogracias Villadolid, of the then Bureau of Fisheries (now known as Bureau of Fisheries and Aquatic Resources), who brought some breeding stocks of tilapia from Thailand into the Philippines in the 1950s. Calling it a “miracle fish,” the bureau wanted it to be raised in backyard ponds nationwide.
But tilapia’s high reproduction rate resulted in overcrowded ponds and stunted fish, and many Filipinos became disappointed over its performance.
The cause of overcrowding was simple. Pond-reared tilapia, with a natural ratio of 50% male and 50% female, mature in 60 days. They breed frequently, often every 30 days. “Female tilapias may spawn from 100 to thousands of eggs, depending on its size,” the Iloilo-based Southeast Asian Fisheries Development Center (SEAFDEC) reports.
At such a growth rate, there was more fish in the pond and competition for food escalated. With reduced nutrition, the best attainable market size for tilapia at that time after four month was only 150 grams.
“Tilapias are prolific,” says Dr. Rafael D. Guerrero III, a fishery expert and an academician with the National Academy of Science and Technology (NAST). Generally, tilapias spawn in shallow portions of lakes, rivers or ponds. In breeding, the male builds nests on the bottom to attract females. The nests are round and shallow, about 20-25 centimeters wide.
“The male waits for the female partner in the nests,” SEAFDEC reveals. “After a brief courtship (to last a few hours), eggs are spawned by the female and fertilized by milt from the male. The female then gathers the fertilized eggs in its mouth to incubate them. The egg hatches after three days. Spawning can occur as often as twice a month during the year if conditions warrant.”
Studies have shown that the male tilapia grows faster and bigger than the female tilapia. The logical choice was to grow all male tilapias. But the challenge is: 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 (NAST). And it could be accomplished through the so-called “sex reversal technique” or SRT. “SRT is the process by which genetic female tilapia fry are converted into functional males through hormone manipulation,” Dr. Guerrero explains.
A sex-reversed tilapia (SRT) is very virile, has a high sperm count, capable of fertilizing five to ten females, according to Dr. Guerrero. Female tilapias are separated from the rest, with a few males added to do the fertilization of eggs.
How does sex reversal occur? When the fry in the breeding ponds or units are about 7 to 10 days old, and about 9 to 11 millimeters long, they are stocked in treatment units. The density of stocking is 250 to 1,000 per square meter. On the first week, they are fed a sex reversal diet containing synthetic male hormones at the rate of two grams per day in four feedings at regular intervals from 8:00 in the morning to 4:00 in the afternoon per 1,000 fries.
For the second week, the feed is increased to 7.5 grams per day. In the third week, the feed rate is 12 grams per day. After the 21-day treatment, the male population ranges from 95-99 percent. The fingerlings are then transferred to regular nursery units or stocked directly in predator-free culture ponds.
Using pollen from pine trees
But farmers can still convert female tilapias into male tilapias without using a commercial sex hormone. 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 explained. “It is an environment-friendly approach and could be an alternative to the use of high-priced standard hormone in sex change.”
The pine pollen came from the three-needed Benguet pine (scientific name: Pinus kesiya). It is the dominant species of the Luzon tropical pine forests. Baguio has earned the nickname, “The City of Pines,” because of the large stands of this tree.
The good thing about CLSU’s pine pollen technology is that it does not cause the deposit of harmful chemicals onto the soil of the pond, which is common in using the standard synthetic 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.
When taken in powder or in liquid form dissolved in alcohol, pine pollen is easily absorbed by tilapia
In the CLSU study, the young tilapia fingerlings with no identified sex were fed with different concentrations of pine pollen dissolved in alcohol for 28 days. About 40 milligrams of pine pollen were added and soaked with 62.5 millimeters of alcohol. After seven days of soaking, the filtered liquid was added to 125 grams of commercial feed, fry mash.
The feed with the pine pollen solution was air dried and fed to the young fish for 28 days. The feed with pine pollen solution was given 6-8 times per day. After the 28th day, the fish fed with pine pollen solution was 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 reported. “In cases it was hard to identify the sex by just looking at the belly, we cut the belly and check the reproductive organ under the microscope.”
On-farm trials to test the feasibility of 100% Benguet pine pollen raw powder was conducted at the Bicol University Tabaco Campus in Tabaco City. The result of the study demonstrated the effectiveness of the pine pollen as an alternative source for synthetic hormone used in sex reversal of tilapias.
“Even as raw powder, pine pollen had a relative advantage in terms of cost, effectiveness and locally available alternative source hormone,” said Dr. Plutomeo M. Nieves, of the university’s fisheries department, who conducted the study.
Breeding male tilapias naturally
Currently, commercially available all-male tilapia fingerlings are produced through the use of steroid hormones. The University of the Philippines Visayas, however, has come up with a new idea: why not develop an efficient protocol to naturally produce male tilapias, or those that bear YY chromosomes.
The project, “Molecular Marker Assisted YY Male Tilapia Production,” is being funded by the Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development (PCAARRD), a line agency of the Department of Science and Technology (DOST).
“Through this project, YY males (or super males) are being developed and will eventually be rolled out to tilapia farmers, allowing them to produce all-male (XY) tilapia progenies through natural breeding,” wrote Rizza B. Ramoran in a press release disseminated by Science and Technology Media Services.
In genetics, pairing females (XX) with males (XY) produces a mix of XX and XY offspring. In this project, the XY males undergo a “feminization process” through oral hormonal ingestion to develop sex-reversed (SR) females with XY chromosomes. These SR females (XY) will then be used to mate with a natural male (XY) to produce male offspring with YY chromosome. With the availability of sex-linked DNA markers, the generation/selection and identification of YY males could be done more efficiently.
The identified YY males will then be mated with SR XY females. Their offspring will undergo another sex-reversion through hormonal ingestion, this time, to generate a female tilapia with YY chromosome. Once these SR YY female tilapias are identified, they will be mated with the YY male to generate all YY male offspring.
These YY male will be mass-produced to serve as broodfish and will be distributed to tilapia hatchery operators. YY male being parent stock are expected to mate with natural females (XX) to generate all-male (XY) tilapia offspring without the use of steroid hormones.
Ramoran said the project aims to develop a YY male technology for the production of all-natural XY male tilapia offspring using the saline-tolerant strain, specifically the UPV-Saline-tolerant Population of Improved Nilotica (SPIN). This strain was developed through funding support from PCAARRD as well.
In addition, the project strives to significantly mitigate the effects of using steroid hormones. Through the use of YY males as parent stock, all-male tilapia production can be achieved through natural breeding without hormone ingestion.
“Through the project, hormone use is only limited during the initial development of sex-reversed broodstock,” Ramoran said.
According to the project, there needs to be more studies in developing YY male technology for saline-tolerant tilapia, especially in the Philippines. With this, the project aims to develop the said technology to boost a more efficient saline-tolerant tilapia aquaculture.
“By limiting saline-tolerant tilapia strains to all-male populations for grow-out culture, possible impacts on its proliferation and invasiveness in marine environments can be mitigated,” Ramoran said.