The story
From janitor + fish, coined by the Filipino locals and as well as the aquarium fish enthusiasts for its ability to clean aquaria by eating algae and fish excrements.
Etymology from Wiktionary, CC BY-SA 4.0.
janitor fish
Today it means: A pleco, pleco fish or plec: Any of several South and Central American fish, of the family Loricariidae. Full definition →