Most fish have scales and are cold-blooded.
Most fish propel themselves through water with weaving movements and control direction with fins.
Although some fish, such as sharks, bear live young, most fish eggs are fertilised and hatch in water. Adipose Fin - This fin most often occurs on characins. Alevin - A juvenile eel. They are marine invertebrates under an inch long that have an exoskeleton and jointed legs. They are eaten in huge numbers by filter feeders such as the whale shark, the basking shark, the megamouth shark, and baleen whales.