When I was a teenager and did not have the Internet I once bought a cute catfish in a fishstore with cow like spots (I was not living in the USA at that time). When the guy in the fishstore caught it, it jumped and fell on the floor. The guy told me I would get my money back if the fish died in the next week. Long story short, I had this catfish in a 50 gallons for several years, he ate all my other fish (I had a couple tropical fish) and, a couple years later, when I went to college, I left my parents in care of my tank which at that time only housed said catfish. One day, my mum called me and told me that he had injured himself by jumping and hitting the top of the tank and that he had died a couple days later. When she got the fish out of the tank, she got stung by something. Her hand got red and swollen for several weeks and she did not know what it was. She thought it might be some kind of infection and got pretty scared. Years later I looked up what kind of species the catfish was. It turned out it was an albino walking catfish (clarias batrachus), which is venomous and has stingers behind his fins. I definitely wished I had known that from the start as I could have warned my family to never touch this fish with bare hands.