I had a 20 gal tank when I was in the Navy. One time when I came home, I didn't see my Leporinus anywhere in the tank. I always felt he was the boss fish in the tank, so I knew he wasn't eaten. I looked all over and found him stuck to the wall behind and below the tank. I peeled him off the wall and plopped him back in the tank. He was fine. I rigged up the top so he couldn't jump out again. Sometimes he'd hit the side of the tank so hard I thought he'd break the glass. I only had about 5 fish in the tank. Whenever I added any more they were immediately eaten.