I once had some bluegills in a floating cage. I went out to feed them and looked down and saw a largemouth in there! Then I saw another! "What the heck!" I thought. "How did they get in there?" Turns out I had failed to fasten a three foot section of an overlap underneath and the bass were getting in and getting easy meals.
I have since learned that fish will find an opening if there is one and are quite the escape and entry artists.