Fishron is a pinkish fish that can be caught Underground in a Snow Biome. Not to be confused with Duke Fishron.
There's a legend of a mighty being known as the Fishron! It's part pig, part dragon, and part FISH! I hear it hangs around in the frozen subterranean lakes of the coldest part of the world! I'm not going there, so YOU go catch it and makes sure it lands in my hands! I'm so excited!