I have several Plecos, the first and biggest got too big for my indoor 55 gallon and I moved him outdoors to my pond. While he was inside he once ate a bullfrog tadpole that I temporarily had inside to view its development. I don't think he is that aggressive of a carnivore, but he probably swallowed it without even noticing it until after it was done. This particular Pleco is very playful and grew up with a Texas Cooter turtle since both were babies. The two were very playful with each other, the Pleco would attach itself to the turtles shell and ride on his back around the tank. Also the Pleco would swim beside and cut off the turtle making it detour and change direction. When the Pleco was attached to the side of the aquarium the turtle would approach within an inch or two and imitate the Pleco's mouth movement.
Once the turtle got too big for the tank and went to the pond, I put a baby Red-Earred Slider turtle in the aquarium and the Pleco was just as playful with the smaller Slider turtle, attaching itself to it's back and sometimes not releasing it for several minutes. A couple of times I was concerned that the Slider turtle might drown for lack of air. So I don't think a well feed Pleco is a vicious carnivore, I just think other smaller species get in it's way and down into his stomach they go, whether out of curiosity or playfulness sometimes they get swallowed. lol
