Yes, a plecostomus will eat other fish. However, plecos will only eat dead or dying fish that sink to the bottom of the tank – they won’t eat other healthy fish.
If you want to stop your pleco from eating dead fish, make sure to feed it a high-quality diet regularly. Your pleco craves protein, and if it’s hungry, it won’t hesitate to eat dead or dying fish.
Additionally, be sure to remove any dead fish from your tank immediately.