Tamable using fish baskets from aberration. They attack the baskets once placed. It is a good strategy to pen then in with fence foundations and walls, or kite them to a pen. Place your basket on the other side of the wall and catch.
Be very carful while crossing the smallest rivers, they might seem weak but usually around 3 of them comes. They also have a pretty big range.Spear can take one of them but for multiple you are going to need a decent armor and a pike.
A piranha is tameable in Abberation using the fish trap. It has to swim into it. Once you release it from the fish trap, it will be tamed. Great tame in packs, they can kill a good amount of low to mid level groups of players.
These things will spawn in your water pen and kill your tames if they're on passive. Make sure you have Dino's to kill them or foundations all around your pen, they've killed so many of my Icthyosaurus' it's not even funny.