S&T Post: Fresh look on the "Janitor Fish"

Fresh look on the “Janitor Fish”

By Dr. Rafael D. Guerrero III
Executive Director, PCAMRD

The “janitor fish,” is considered a nuisance species in Laguna de Bay and the Marikina River . This South American aquarium catfish introduced in the country possibly by hobbyists has escaped into local freshwaters.

The Philippine Council for Aquatic and Marine Research and Development of the Department of Science and Technology recently issued updates on the “janitor fish”.

First, there are two species of the “janitor fish” that have been correctly identified by senior fishery biologist Edna Agasen of the Department of Agriculture’s National Fisheries Research and Development Institute with the assistance of Dr. Jonathan Armbruster, curator of fishes at Auburn University (USA). The species are Pterygoplichthys pardalis found in the Marikina River and Lake Paitan in Cuyapo, Nueva Ecija; and the Pterygoplichthys disjunctivus found in Laguna de Bay.

This new report now corrects the previous identification of the “janitor fish” as Plecostomus hypoglosus in the country.

Studies indicate that the “janitor fish” has also become invasive in other countries. According to Dr. Armbruster, the Pterygoplichthys species have become established in tropical and semi-tropical regions of North America , Puerto Rico , Malaysia , Indonesia and possibly other places where these were introduced.

In spite its unpleasant reputation, the “janitor fish” is edible. It is eaten by South Americans who usually gut and grill them whole or make soup with them, says Dr. Armbruster. The fish can survive up to 30 hours or more out of water as long as they are kept moist. This applies well in rural areas where refrigeration is not available.

The “janitor fish” caught in Laguna de Bay has been declared safe for human consumption by Jose Cariño of the Laguna Lake Development Authority. It does not contain toxic levels of heavy metals.

Dr. Armbruster says, “the fish builds its nests in mud banks and can contribute to water turbidity.” They may compete with other fishes feeding on algae and detritus (organic matter) on the bottom. In its natural habitat, it feeds on tadpoles and insects.

There appears some practical control measure that can be applied for the “janitor fish”. Since the “janitor fish” breeds and grows quickly, Dr. Armbruster suggests that the best way to reduce its population is by catching the adults through grill nets or traps at their nesting sites.

In the United States , the fish does well in reservoirs and canals than in natural freshwater bodies, he said.

The LLDA is implementing a World Bank-funded project to reduce the population of “janitor fish” in Laguna de Bay by paying fisherfolk P10 per kilogram of the fish which is converted into fishmeal for pig feed by a cooperative in Siniloan Laguna.