Pilot fish usually gather around sharks (as well as rays and sea turtles). They eat parasites (very small creatures which feed off other animals) on their host, as well as small pieces of food that their host does not eat (leftovers). When pilot fish are young, they gather around jellyfish and drifting seaweeds.
Pilot fish follow sharks because other animals which might eat the pilot fish will not come near a shark. In return, sharks do not eat pilot fish because pilot fish eat the parasites which feed off sharks. This is called a "mutualist" relationship. Small pilot fish are often seen swimming into the mouth of a sharks to eat small pieces of food from the shark's teeth. Sailors even said that sharks and pilot fish act like close friends. When a ship would capture the shark the pilot fish followed, some people reported that the pilot fish would appear upset and follow the ship for up to six weeks.
The pilot fish is of a dark blue to blackish-silver colour, and are slightly lighter in colour underneath. They have between 5 and 7 dark stripes going from top to bottom. When the fish is excited, these stripes disappear, and three large blue patches appear on its back. The pilot fish is usually about 30 cm long, but sometimes they can be as big as 70cm.
The pilot fish will not hurt people, and they are said to be good to eat. They are very difficult to catch, though.
There are many explanations for the name "pilot fish". It could be because sailors people believed that pilot fish were leading (piloting) them back to port, or even leading swimmers and whales to safety. It could also be because people used to think pilot fish would lead sharks to food (but they do not really do this).
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- NOAA Library Image: http://www.photolib.noaa.gov/historic/nmfs/figb0368.htm