Saving ayungin from extinction-A A +A
Sunday, January 27, 2013
ALTHOUGH ayungin is two to three times more expensive than tilapia and bangus, it is still in great demand.
"Despite the decline of ayungin populations and commercial catches within Laguna de Bay in recent years, the demand remains very high," the Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development (PCARRD) has reported.
A small freshwater fish scientifically called "Leipotherapon plumbeus," ayungin is indigenous in Laguna de Bay. As it is well-adapted to lake water, it has been introduced in Taal Lake in Batangas and Naujan Lake in Mindoro. It is dubbed as silver therapon, which is related to Australia's silver perch.
Although it typically grows to a maximum length of about 15 centimeters, ayungin is very popular in Southern Tagalog provinces including Laguna, Rizal, Cavite, Batangas, and Metro Manila because it is touted as the tastiest among all the edible native freshwater fishes.
In proportion to its size, ayungin is one of the most expensive fish in the Philippines. Prices depend per region, but the average price range is P200 to P800 per kilo (dried) and around P300 fresh (or more depending on the weather and season). It is now rarely seen in the market.
"In earlier times, ayungin remains abundantly found in Laguna de Bay waters and in other freshwater systems," the Pcarrd said. "As such, there were no good reasons to mass culture ayungin then."
However, some studies were conducted on ayungin in terms of its distribution, feeding habits, population genetic structure, and pattern catch landing. There were no previous attempts made to artificially produce ayungin in captivity like tilapia, bangus, and lapu-lapu.
"The fish has not been considered as an aquaculture species," the Pcarrd said.
There might have some attempts in the past to culture ayungin but may not be successful. Other related reasons include the lack of cost-effective spawning agents and techniques in the production of live feeds required for larval culture.
Generally, females are larger than males. It is an omnivorous fish feeding on zooplanktons and phytoplanktons, small shrimps, eggs of other fish, and even insects.
Ayungin is a middle water swimmer; it is not bottom dwellers or surface swimmers. They swim in big schools, close to each other as defense against predators like the snakeheads and water snakes.
Unlike other freshwater fish, ayungin has no distinct breeding season. It breeds throughout the year, with high rates of spawning from July to September, although good spawning occurs in December and January. "The high spawning period coincides with the onset of the rainy season," the PCARRD said.
To save ayungin from extinction, researchers at the University of the Philippines at Los Baños (UPLB) have developed a surefire method that calls for induced spawning. Under the process developed by scientists of the university's Limnological Research Station (UPLB-Limno) in Mayondon, Los Ba¤os, chemical hormones are used to induce the spawning of ayungin.
The broodstock are obtained from Laguna de Bay, Naujan Lake and Taal Lake. "Before the hormone treatment, fishes are taken from their maintenance aquarium tanks and temporarily stocked in a basin with two parts per thousand (ppt) salt solution," noted the Pcarrd publication, "Induced Spawning and Larval Rearing of Ayungin." "The fishes are then sedated by soaking in iced water for about 10 seconds or until they are immobilized."
A volume of 0.02 milliliters of the prepared hormone - human chorionic gonadotropin (hCG) - concentration is then introduced into the fish, both male and female. This is done through intramuscular route along the dorsal portion of the body using a 26-30 gauge needle, irrespective of fish size.
The treated fish are then allowed to recover in 2 ppt saline solution for about five minutes or until they have fully recovered.
"Breeders are returned to their well-aerated maintenance aquarium tanks to permit spawning," the PCARRD publication informs. "The breeders are normally kept in their breeding tanks at a female to male ratio of 1:2 per tank."
According to the PCARRD publication, the latent period for spawning ranges from 22 to 40 hours. "They spawn in a conventional aquarium tank kept at room temperature (24-28 degrees Centigrade)," it says. "The same tank is also used as incubation container for fertilized eggs which are found scattered at the bottom of the tank."
Published in the Sun.Star Davao newspaper on January 28, 2013.