Fish | Definition, Species, Classification, & Facts

What makes a fish a Fish?

All fish are cold-blooded aquatic animals. They have a backbone, fins, and gills. Fish are one of the most interesting and diverse animals in the animal kingdom.

Highlights of Fish:

Kingdom Animalia
Phylum Chordata
unranked Craniata
Subphylum Vertebrata

Types of Fish

Fish are more diverse than any other group of vertebrates. There are 32,000 different species of fish. There are three main types or classes of fish including jawless fish, cartilaginous fish and bony fish. An example of a jawless fish is the lamprey. Sharks are cartilaginous fish and marlins are bony fish.

The fish vary in all sorts of colors and sizes. The fish can grow up to 40 feet long and 1/2 inch long. There are aquatic animals that we might think of as fish, but are not actually classified as fish by scientists. These include whales, dolphins, octopuses, and jellyfish.

Fish Breathe Water

All fish have gills that allow them to breathe underwater. Just as we use our lungs to exchange oxygen for carbon dioxide from the air, the gills of fish perform the same function from water. So fish always need oxygen to live, they only get oxygen from water instead of air.

Where do Fish live?

Fish live in most of the world’s major bodies of water, including streams, rivers, ponds, lakes, and oceans. Some fish live on the surface of the water and some live in the depths of the ocean. There are fish that live in freshwater and others that live in salt water.

What do Fish eat?

Some fish species eat plants. They can scrape algae from rocks or eat plants that grow in the ocean or sea. Some fish, called carnivores, eat other fish and animals. Sharks are famous predators that hunt their prey. Other predators stalk their prey by hiding in sand or rocks to ambush their prey.

Groups of Fish

A group of fish is called a school. Some species of fish congregate in schools and are therefore more difficult to catch. A predator becomes confused when attacking a shoal and sometimes fails to catch any fish. A loose group of fish is called a school.

Biggest, Smallest, Fastest Fish

The largest or heaviest fish is the bass that can weigh up to 5,000 pounds.

The longest fish is the whale shark, which is known to be over 40 feet in length.

The fastest fish is the sailfish that can swim up to 68 miles per hour.

The smallest fish is the orcas with a length of only 9 mm.

Fish as Pets

Many people like to keep fish as pets. There are special tanks and food you can get to take care of your fish. They can be very interesting and also very beautiful to look at. While it is fairly easy to care for as a pet, you will need to do a bit of work. You must keep the aquarium clean and make sure that you feed the fish the right amount each day.

Interesting Facts About Fish

Whales cannot swim backwards. A jellyfish is not really a fish.

Some fish, such as the spotted rock perch, can breathe oxygen from the air.

Many fish have internal air sacs that help them float. Those that do not, like sharks, must swim or they will sink.

Baby sharks are called baby sharks.

An electric eel can deliver a powerful electric shock of up to 600 volts.