Janitor fish threatens Asia’s largest marshland
- Mike Baños () - June 6, 2006 - 12:00am
CAGAYAN DE ORO CITY — The janitor fish infestation that has plagued Marikina River and Laguna de Bay has also spread to Mindanao, and is now threatening to run riot across the delicately balanced ecosystem of Asia’s largest marshland, the Agusan Marsh in Agusan del Sur.

There are currently two species of janitor fish in the country as identified by Edna Agasen, senior fishery biologist of the Department of Agriculture’s National Fisheries Research and Development Institute, with the assistance of Dr. Jonathan Armbruster, catfish expert and curator of fishes at Auburn University in Alabama, USA.

These are Pterygoplichthys pardalis found in the Marikina River and Lake Paitan in Cuyapo, Nueva Ecija; and the Pterygoplichthys disjunctivus found in Laguna de Bay (not Plecostomus hypoglosus as previously reported).

Studies indicate the janitor fish has also become a pest in other countries. Armbruster said the Pterygoplichthys species has become established in tropical and semi-tropical regions of North America, Puerto Rico, Malaysia, Indonesia and possibly other places where they were introduced. In the US, the fish does better in reservoirs and canals than in natural freshwater bodies, he said.

Marianne Hubilla, a volunteer fisheries researcher with the Provincial Environment and Natural Resources Office (Penro) from the University of Philippines in the Visayas (UPV), and Ferenc Kis, a Hungarian consultant on wetland management, accidentally discovered the proliferation of the janitor fish in the Agusan Marsh while preparing a project proposal for a taxonomic survey on freshwater fish, mollusks and crustaceans in La Flora, Talacogon, Agusan del Sur last March 8.

The two were surprised to see a fisherman removing a janitor fish from a gill net, but became alarmed when they saw another fisherman landing 50 janitor fishes in San Marcos, Bunawan, Agusan del Sur last May 22.

Hubilla said Armbruster identified the species through their photographs as Pterygoplichthys disjunctivus, or the same species found in Laguna de Bay. It belongs to the largest catfish family and is native to the Madeira River drainage of the Amazon River in South America.

According to Armbruster: "The fish builds its nests in mud banks and can contribute to water turbidity."

They may compete with other fish feeding on algae and detritus (organic matter) on the bottom. In its natural habitat, it feeds on tadpoles and insects, he added.

In a paper titled "Janitor Fish in Agusan Marsh: A Threat to Freshwater Biodiversity," Hubilla warns that janitor fish "competes for food with the native catfish, carp, mudfish, tarpons, mullets, tilapia and other fish species found in the marsh. They also compete with bivalves and gastropods for food."

Hubilla said this could alter the aquatic and faunal composition of Asia’s largest marshland which freshwater biology researchers have yet to fully explore.

"Since they (janitor fishes) are opportunistic and voracious feeders, they may cause their numbers to increase enough to disrupt the marsh ecosystem by displacing the native fish species, and causing the reduction of native fish catch. What is worrisome is that the janitor fish has no natural enemies in the Agusan Marsh and this means it can rapidly multiply," Hubilla said.

A Haribon Foundation report prepared by Simplicia Alonzo-Pasicolan and Perla Magsalay describes the 89,359-hectare Agusan Marsh as a vast complex of freshwater marshes and water courses with numerous small shallow lakes and ponds in the upper basin of the Agusan River and its tributaries. It is located near Bunawan in the interior of northeastern Mindanao Island, in the Agusan River Basin, Agusan del Sur province.

Some 42,000 hectares of the marshlands have been declared a "World Heritage Conservation Site" of the Agusan Marsh Wildlife Sanctuary by MAB Philippines/Protected Areas and Wildlife Bureau due to its identification as a center of floral and faunal diversity with seven habitat types.

It harbors the most diverse assemblage of reptiles and amphibians and supports the largest remaining population of the Estuarine Crocodile Crocodylus porosus in the Philippines, and is also believed to harbor the endangered Philippine crocodile, or C. mindorensis.

It is also one of the few sites that has combined high ecological value with high viability, in terms of the following ecological criteria: high habitat diversity and distribution; rare wetland plants and wetland vegetation richness; wetland bird species and number; presence of rare, endemic endangered birds; and richness and endemism of fish species.

The wetland supports a small subsistence fishery, and is an important source of water for irrigation. It is sparsely populated because of the annual flooding of the Agusan River. Besides fishing, inhabitants’ sources of livelihood include some aquaculture and agriculture, mainly rice and cash crops.

Parts of the marsh has already been converted into aquaculture ponds and rice paddies, and large-scale drainage is being considered. The crocodiles are heavily persecuted. Clear-cutting of forests in the water catchment area has resulted in severe flooding when the rivers rise from November to March and increased rates of sedimentation in the wetland.

Harmless janitor?

But the Department of Science and Technology’s (DOST) Science and Technology Information Institute S&T Media Service, in a statement by Rodel Offemaria dated Aug. 21, 2002, quoted the Philippine Council for Aquatic and Marine Research and Development (PCAMRD) as declaring the janitor fish to be harmless to man and aquatic life.

PCAMRD said its spine is not poisonous and its flesh is edible. Janitor fish were previously bred in ponds in Laguna but escaped into Laguna de Bay and nearby river systems. The fish digs up holes in pond dikes and river embankments for breeding nests.

When feeding on algae growing on the nets of fish cages in Laguna de Bay, the janitor fish’s rasping mouth can cause jagged cuts in nets, resulting in the release of cultured fish. Although not a food fish, it can be utilized as raw material for fish meal and fish leather because of its unique-looking and textured skin.

But Armbruster says the janitor fish are eaten by South Americans who usually gut and grill them whole or boil them as soup stock. Since it can survive up to 30 hours or more out of water provided it is kept moist, janitor fish are ideal for rural areas where cold storage is not available.

Jose Cariño of the Laguna Lake Development Authority (LLDA) has also declared the fish caught from Laguna de Bay as safe for human consumption since they do not contain toxic levels of heavy metals.

Armbruster believes some practical control measures can be used to prevent the proliferation of janitor fish. Since it breeds and grows quickly, he suggested the best way to cut down its numbers was to catch adults with grill nets or traps at their nesting sites.

The LLDA is implementing a World Bank-funded project to control the janitor fish population in Laguna de Bay by paying fisherfolk P10 per kilogram for the fish. The catch is then converted into fishmeal for pig feed by a cooperative in Siniloan, Laguna.

Commercialization of janitor fish was also suggested by a research project in this year’s field Intel Phil. Science Fair supported by the ChED and the DOST. Raymond Joseph Amurao of Marikina Science High School entitled his project, "Biofuel and Soaps from Janitor Fish (Pterygoplichthys pardalis)," inspired by Marikina’s acute janitor fish infestation problem. Amurao was able to extract fuel oils from janitor fish carcasses, material that could then be used in practical applications such as diesel additives and soap base.

Hubilla and Kis recommend that a long-term study of the reproductive biology and ecology of the janitor fish be undertaken locally.

"As of now, it is too late to ban the entry of janitor fish... The only scientific solution is to conduct a rapid study on the population and distribution of this fish in the marsh... Knowing these facts will generate insight on how to control and eradicate the fish," the paper concludes.

Over and above all these should be stricter controls on the trade and movement of imported tropical fish, the authors said.

"The successful invasion of janitor fish in the Laguna Lakes and nearby rivers, and more recently in the Agusan Marsh, implies that the concerned agency (DA) is not properly enforcing the law." Republic Act 9147, mandates the agriculture department’s bureau "to enforce the registration, permits and clearances of all imported exotic species."
Wake-up call
The janitor fish infestations of the Agusan Marsh, Marikina River and the Laguna Lake and its tributaries should serve as a wake-up call to the bureau to strictly enforce regulations to prevent accidental or intentional release of destructive fish species into Philippine waters.

"The tragedy of the janitor fish invading our inland waters is all too real, and the Department of Environment and Natural Resources (DENR) has been sleeping on the job," echoed Dr. Rene Lacanilao of the Medical City in a recent e-mail to a national broadsheet.

Lacanilao cites how wildlife authorities in Maryland, USA, had to use poison, electrocution and draining after an inland river and a lake were invaded by a snakehead, a voracious fish species not indigenous to the area that had threatened to decimate the local fish population. He also cites how Guam virtually lost all of its endemic bird species after an "alien" brown tree snake was inadvertently imported by immigrants to the island.

"At the first sign of the janitor fish, the DENR should have shut down the entire Marikina River and maybe poisoned its entire length. Now the problem has spread throughout the Manggahan floodway into the Laguna Lake. It may now be too late to contain it and we may soon find some of our local fish species disappearing from our waters," Lacanilao wrote.

Commercialization of unique species endemic to an area could be another incentive to control the entry of exotic fish that could affect an area’s future potential.

For instance, in 1984 Ross suggested that the Agusan Marsh be made into a crocodile sanctuary if the local inhabitants could be convinced to ranch or crop crocodiles on a sustained-yield basis. Taxes and other revenues from this initiative could then be utilized for other related developments to maintain the ecosystem such as declaring parts of the water catchment area as protected areas to reduce soil erosion and sedimentation including an area of 5,363 hectares to be designated as a reserve for the reintroduction of the Eastern Sarus Crane (Grus antigone sharpie).

Other proposed development projects in the water catchment area include the construction of dams and reservoirs for hydroelectric, flood control and irrigation purposes.

The Agusan Marsh is also an important area for a variety of water birds, notably herons and egrets such as Bubulcus ibis (over 500), Ardea purpurea and A. cinerea (over 200). The Eastern Sarus Crane Grus antigone sharpii, now extinct in the Philippines, was last recorded in Agusan Marsh in 1965.

  • Latest
Are you sure you want to log out?

Philstar.com is one of the most vibrant, opinionated, discerning communities of readers on cyberspace. With your meaningful insights, help shape the stories that can shape the country. Sign up now!

or sign in with