If you’re trying to catch a Piranha for your Sim’s Fish collection, you’ll need a fairly high Fishing skill and the right bait.
Your Sim needs to reach level 8 Fishing before Piranha can be caught.
Using bait is also a good idea. Catfish, Koi, and Rainbowfish are useful bait options, but if you don’t have any of those, a medium-sized fish will work too.
One of the better places to catch Piranha is the fishing spot at the back of Oasis Springs Park. Head toward the rear of the lot, near the mine entrance, and look for the fishing spot.
Koi is a good bait choice here and can help with your chances of getting a Piranha.
You can also catch Piranha in Willow Creek and in Sylvan Glade.
If you’re fishing in Sylvan Glade, try using Treefish as bait. Piranha seem to be easier to catch there when using Treefish.
If you’re having trouble finding one, I’d start with the fishing spot in Oasis Springs before trying the other locations.
If you’re completing the Fish collection, keep your first Piranha somewhere safe. You can mount it on a wall as a trophy or put it in an aquarium if you want to keep it around.
Just don’t leave it sitting in your Sim’s inventory for too long. Fish spoil quickly, even when they’re stored in the fridge.
You can also use caught fish as fertilizer for gardening or stock them in a home pond if you want to keep them from spoiling.