In Scribblenauts, Fish can be fed to cats, big cats, and other carnivores. Living fish can be put on a heat-giving device to cook it.
In Super Scribblenauts, carnivores and omnivores will usually accept it. A dead fish must be placed on a stove or something like it to turn it into food. Using a dead blowfish to make food will result in Poison Seafood, and shouldn't be eaten.