Fish live in water. They are also vertebrates, meaning that they have a backbone. In addition, they use gills to absorb oxygen to breathe. They also lay eggs. Most fish are cold-blooded, and some fish have scales.
There are about 30,000 known species of fish.

One example of a fish is the common seahorse, or
Seahorses are the only fish

that swim upright.

Another example is the striped eel catfish, or


This catfish has venom stored in its spine that may be fatal to humans.
http://biology.clc.uc.edu/courses/bio106/chordate.htm

http://www.nhc.ed.ac.uk/index.php?page=493.450