It may be small, but dynamite comes in small packs.
The most dangerous fish in the world is the Candiru catfish, AKA toothpick fish. They are around 15 centimeters, but they are more dangerous than any kind of shark or piranha. The Candiru is most commonly found in the Amazon river. They attack by lodging itself in your urethra, vagina, or your anus. It is attracted to urine so bathers in the region are warned to not urinate while bathing. A famous case of a Candiru attacking a human was recorded when a Candiru lodged itself into a fisherman’s penis. Long hours of grueling surgery finally got the Candiru out, but it had already caused a lot of pain. The Candiru’s normal prey are big fish. They hook themselves onto the fish and starts to suck blood from them. Here are a few pictures.
A Normal Candiru
The famous Candiru that got surgically removed from a man’s penis.
Candiru attacking a fish.