I believe the question relates to the group of animals within the animal kingdom which is labeled as fish.
Fish are back boned animals that live in water. The various kinds of fish differ so much in their shape, colour, and size that they do not seem to have much in common to be classified in a common group of animals.
However, all fish have two main features in common. First hey have a backbone, and so they are vertebrates. Second, they breathe mainly by means of gills. Nearly all fish being cold-blooded animals, cannot regulate their body temperature, which changes with the temperature of their surroundings. Also, almost all fish have fins, which are used for swimming.
Not all animals living in water are classified as fish. They differ from fish in at least one of these ways. For example, Dolphins, look like fish and have a backbone and fins, but they are breathe with lungs rather than gills, and they are warm-blooded. Some water animals such as jellyfish and starfish are called fish, but they do not have a backbone and so are not fish.
To identify an animal as a fish , it should have these characteristics:
- Fish live in water.
- Fish have a backbone . They are vertebrates.
- Fish breathe using gills. They absorb oxygen through the gills.
- Almost all fish are cold - blooded. ...
- Some fish have scales .
Characteristics of fish are as follows:-
- Fishes are cold blooded mammals. There body's internal temperature is not constant and adjusts according to the environment.
- Fishes contain scales that protect them from being injured or infected
- Gils make them inhale oxygen in water
- Fins help fishes to swim
- Fishes can see whatever's happening around them
- Fishes have no ears but still they can sense things and activities taking place in and above the water.
- Fishes have unique cells that help them move around water
- Fishes can sense the dangers approaching them
- Some fishes blend in the environment by changing their color.
- By releasing male and female sperms at the same time reproduction takes place
- Normally the shape of fishes is cylindrical as to make swimming easy in water
- Some fishes have light on their heads as to see through dark and attract their prey