Fish are aquatic dwelling animals that breathe through gills. Most fish are cold blooded, meaning that instead of creating their own heat their body temperature is determined by their environment. There are about 34,300 described species of fish, making them the most diverse out of any type of vertebrate. Fish come in a wide variety of sizes from the 0.3 inch (8mm) stout infantfish to the 52ft (16 m) whale shark.