From WoWWiki

Most of the creatures you catch with the Fishing profession are fish.

Overview

In World of Warcraft, fish can mean a few things:

1. (noun) One of six types of food in WoW. Hunter pets will each only eat certain types of food (a few will eat any).
2. (noun) The aquatic creatures you catch with the Fishing profession for eating, use in Cooking, as an ingredient for other recipes, or other uses. Not necessarily fish biologically.
3. (noun) Non-edible inventory items with a fish graphic, from some other source. These sometimes appear as quests items.
4. (noun) Aquatic mobs that are fish, such as the frenzy and shark mobs.
5. (noun) A graphic critter sometimes seen in water, representing the presence of fish.
6. (verb) The act of Fishing to catch fish or other objects.

See also: Fish, Fishing, Things caught by fishing