Fish are some the most interesting and varying types of animals in the animal kingdom.
What makes a fish a fish?
All fish are cold-blooded animals that live in the water. They have backbones, fins, and gills.
Types of Fish
Fish come in more varieties than any other group of vertebrate animals. There are 32,000 different species of fish. There are three major types or classes of fish including jawless, cartilaginous, and bony fish. An example of a jawless fish is the lamprey eel. Sharks are cartilaginous fish and the blue marlin is a bony fish.
Fish vary in all sorts of colors and sizes. Fish can be as large 40 ft long to 1/2 inch long. There are some animals that live in the water and we may think of as fish, but really aren't classified by scientists as fish. These include whales, dolphins, octopus, and jellyfish.
They Breathe Water
All fish have gills that allow them to breathe water. Just like we use our lungs to exchange oxygen for carbon dioxide from the air, the gills of a fish perform a similar function from water. So fish still need oxygen to live, they just get it from the water instead of the air.
Where do they live?
Fish live in nearly every large body of water in the world including streams, rivers, ponds, lakes, and oceans. Some fish live on the surface of the water and some live in the very depths of the ocean. There are fish that live in fresh water and others that live in salt water.
What do they eat?
Some fish eat plant life. They may scrape algae off rocks or eat plants that grow in the ocean or sea. Some fish, called predators, prey on other fish and animals. The shark is a noted predator that hunts for prey. Other predators lay in wait for their prey by hiding in the sand or rocks in order to ambush their prey.
Groups of fish
A group of fish is called a school. Some fish gather in schools so they are harder to catch. A predator will get confused when attacking a school and sometimes can't catch any fish at all. A loose grouping of fish is called a shoal.
Biggest, Smallest, Fastest
The biggest, or heaviest, fish is the ocean sunfish which can weigh as much as 5,000 pounds.
The longest fish is the whale shark which has been known to grow to over 40 feet long.
The fastest fish is a sailfish which can swim as fast as 68 miles per hour.
The smallest fish is the dwarf goby at only 9mm long.
Shark Source: USFWS
Fish as Pets
A lot of people like to have fish as pets. There are special aquariums and food you can get to take care of your fish. They can be fun to have and also beautiful to look at. Although they are fairly easy to take care of as pets, you will need to do some work. You need to keep the aquarium clean and make sure to feed your fish the proper amount each day.
Fun Facts About Fish
Whales can't swim backwards.
A jellyfish isn't really a fish.
A few fish, like the spotted climbing perch, are able to breathe oxygen from the air.
Many fish have an internal air bladder that helps them to float. Those that don't, like sharks, must swim or they will sink.
Baby sharks are called pups.
An electric eel can produce a powerful jolt of electricity of up to 600 volts.