In Tanay, Rizal, predator knife fish ends up as fertilizer

LOS BAÑOS, Laguna—The town of Tanay in Rizal province is turning knife fish caught from Laguna de Bay into organic compost to address the growing population of the predator species that continues to threaten local aquaculture.

The knife fish (Chitala ornata) is an ornamental species that the Laguna Lake Development Authority (LLDA) had earlier said found its way into the lake by having escaped from an aquarium at the height of the 2009 Tropical Storm “Ondoy.”

With a body shaped like a knife and razor-sharp teeth, the carnivorous species feed on the fingerlings of other native species in the lake such as bangus (milkfish), tilapia, “ayungin” and “biya.”

“Actually, the fishermen are not trying to catch them (knife fish) but they’re just too many and they happen to be among the regular catch, sometimes even more (knife fish) than the bangus or tilapia being caught,” said Tanay environment officer Carlos Inofre Jr.

Based on their studies with the Bureau of Aquatic Resources (BFAR), Inofre said the knife fish spreads so fast that each could lay about 20,000 to 60,000 eggs in one cycle. A knife fish that weighs one kilogram is also equivalent to about seven kilos of other fish species that it has consumed.

Fish swap

“A knife fish could grow to as long as one meter and weigh as much as 10 to 15 kilos,” added Inofre, in a phone interview on Monday.

The local government of Tanay led by Mayor Rafael Tanjuatco launched on Jan. 17 a program wherein fishermen could swap the knife fish for organic compost.

For every kilo of the fish, a fisherman receives 2-kilogram packs of organic compost from the municipal government.

The municipal government has designated a spot, locally referred to as the “parola” (lighthouse) in Barangay San Isidro, where fishermen could in turn sell the compost to local plant growers for P5 per kilo.

But what happens then to the dead fish? “They now become the organic compost,” he said.

Since 2007, Tanay has been using its own bioreactor, a one-ton heavy machine at its material recovery facility, to convert the community’s biodegradable wastes into soil fertilizer in a three-week process.

The LLDA and BFAR also have different programs to address the knife fish invasion. One of them is to process the knife fish into fish balls, a popular Filipino street food. But although safe for human consumption, the knife fish remains an unpopular choice for human food in the markets.

“They also have not been implemented fully yet down the local communities, so we want something that fishermen can benefit from on the spot,” Inofre said.

Tanay, he said, has four out of 19 villages, situated along Laguna de Bay, with communities relying heavily on the aquaculture industry.