505. Why is fish eaten without being slaughtered in the name of the creator?

Verses (5:96, 16:14) of the Quran say fish can be used as food. Prophet Muhammad had said while all other meat animals need to be slaughtered for food, the fish are not required to be done so.

There exists a doubt in the minds of people, while all the other meat animals are required to be slaughtered before being used as food, why is the fish exempted?

There is a difference between aquatic and terrestrial animals. 

Fishes have the simplest circulatory system where its blood would not flow profusely if they are slaughtered, as in the case of other vertebrates. In Islam blood from animals slaughtered is prohibited from being consumed.

When cattle are slaughtered alive, blood oozes out, and when already dead animals are cut for consumption, we are faced with a plight to consume their blood that has clotted within them along with the meat. There may be microorganisms and germs that remain along with the blood that had clotted in the body of the dead cattle, the vectors in the blood start spreading to other parts of its body, and cause harmful effects when consumed. 

Since the fishes have the barest circulatory system, even if cut, we do not witness profuse bleeding, and even after death the blood in fish do not have the capacity to intrude into its muscles. The reason Islam says here is no need to slaughter fish before being used as food.