Red mostly eats only fruit. Frugivore is the scientific term. He certainly doesn’t eat meat, though some of the other characters do. This means he is just fishing for sport.

This fish represent a lot of firsts. It’s the first non-Grumble character, the first character to use more than one color, notably with eyes a different color than the rest of its body, and, perhaps most importantly, it is the first and only character with a nose. The fish will continue to torment Red for some time. I don’t know if this is out of any personal animosity, or if the fish just doesn’t like people and since Red is the only one who spends a lot of time in the water it naturally antagonizes him the most.