Janitor fish Pterygoplichthys disjunctivus in the Agusan Marsh: A threat to freshwater biodiversity

Abstract

The aim of this study is to verify reports on the presence of invasive alien catfish, known locally as janitor fish, including their possible impact on freshwater biodiversity in the Agusan Marsh, Northeastern Mindanao in southern Philippines. Morphological analysis, field sampling and questionnaire survey were conducted to determine the exact taxonomic status, habitat, distribution, and the population and size estimates of the fish. The results showed that the South American vermiculated sailfin catfish, Pterygoplichthys disjunctivus, a species earlier reported from Laguna Lake and nearby rivers in Luzon, northern Philippines, has invaded the Agusan Marsh. The exotic fish can be found in lakes, rivers and creeks of the municipalities of Talacogon, La Paz, Loreto, Bunawan, Rosario, San Francisco, Veruela and Sta. Josefa. They may also be present in upstream and downstream areas. Total catches of fishermen ranged from 0 to 146 individuals per fishing trip. Practical control measures to reduce the janitor fish population in the Agusan Marsh were discussed.