Fish are vertebrates (vertebrates have backbones) that live in water. They breathe using special organs called gills.

A shadowy shape is visible in the distance, just under the surface of the ocean. The shadow swims closer, revealing itself to be a shark—an incredibly massive shark. Weighing as much …

A whale shark the size of a school bus swims slowly near the surface of the ocean. Its wide mouth is open, like an enormous net scooping up whatever happens to be around—mostly small fish, …

Meet the real "Nemo," the colorful clownfish. Find out how these fish can reproduce even though all their young are born male.

Get your arms around the largest fish in the sea—whale sharks weigh in at up to 60 tons. Find out what tiny creatures keep these gentle giants alive.

How to be a smart fish eater.Many kids turn up their noses at the thought of eating fish because, well, it can smell “fishy.” While it is usually a healthful source of protein in the diet, there may …

A betta fish (Betta splendens) photographed in Lincoln, Nebraska. Also known as Siamese fighting fish, they originally hailed from Southeast Asia but are now popular pets found in …

Sharks can rouse fear and awe like no other creature in the sea. Find out about the world's biggest and fastest sharks, how sharks reproduce, and how some species are at risk of …

Meet the incredible parrotfish, whose coral-crunching bite can be heard on tropical reefs worldwide. Find out how they change genders to promote a harem lifestyle.

There are many breeds of goldfish (Carassius auratus). This is a celestial eye goldfish, which has large eyes turned upward.