Examine various animals from this group to determine similarities among them. You might observe guppies, goldfish, and/or various tropical fish in an aquarium.

Most of the animals of this group live in water, have interior skeletons, have scales for body covering, have fins for locomotion, breathe by means of gills, and hatch from
eggs laid in water.

They feel cool to the touch because they are cold-blooded -- their body temperature is nearly the same as the temperature of their environment. Most fish live in salt water. Some live in fresh water, and a few fish can adapt to either salt or fresh water. About twenty thousand species of fish have been identified.

In the project category called "Ecology," numbered C241.01, et seq, are several lengthy entries dealing with fish and setting up both salt-water and fresh-water aquaria.

Put a goldfish in a wide-mouthed jar half-filled with water. Place a thermometer in the jar so that it can be read without disturbing the fish. Record the temperature of the water and the number of times the fish's gills beat in one minute.

Add crushed ice to the water very slowly. If you just dump it in, you will excite the fish. Continue adding ice until the temperature is near freezing (32 degrees F). Again, count the number of gill beats in one minute.

Next, add warm water to the jar, also very slowly, until the temperature is raised by 5 degrees. Record the gill beats per minute. Continue adding warm water by 5 degree intervals until the temperature reaches 86 degrees F.

By studying the gathered data, you will be able to tell what happens to the fish's respiration rate as temperatures increase or decrease.