This item can be fished from a School of Red Snapper, and drops from Angry Murlocs. It is fished with a provided for the quest, not with a fishing pole, and does not require the fishing skill to fish. The net is used while standing or swimming in a School of Red Snapper, and either catches a single Red Snapper or occasionally spawns a hostile Angry Murloc mob, which always drops a Red Snapper when defeated.
As a quest objective
Red Snapper is strictly a quest item, and cannot be eaten nor fed to hunter pets. You can only catch these while on the quest. You can catch an excess above your needs for the quest, but the turn-in will only consume ten of these. The additional ones serve no purpose; they have no vendor value, and they cannot be transferred to another character.
In any case, red snapper is very much a popular real world fish.