Catch it in the ocean during summer, from 12:00 PM to 4:00 PM, on sunny days
Catch it in the ocean during summer on Ginger Island, from 12:00 PM to 4:00 PM, on sunny days
Buy it from the Traveling Cart when available
Obtain it from a Fish Pond with pufferfish population
Use Magic Bait to catch it outside the normal season, time, or weather requirements