Yes, pleco fish eat other fish. Plecos are opportunistic omnivores, so they might eat dead or dying fish that sink to the bottom of the tank. However, due to their peaceful and docile nature, plecos won’t attack or eat healthy fish.
With that said, plecos are notorious for sucking on the slime coats of other fish. This behavior can be dangerous for the other fish because the victim will become vulnerable to diseases and could eventually die. Goldfish and guppies are the most common victims, but plecos can also target larger fish.
To prevent your pleco from sucking on the slime coats of other fish, provide the pleco with a varied and high-protein diet. Also, feed it one to three times a week.