What are hatchet fishes?

It seems a strange name but some of these fishes really look like a hatchet or chopper. They are very thin fishes, flattened from side to side. The front half of their body is very deep and shaped like a blade. There are two groups of hatchet fishes, one that lives in the sea and one that lives in fresh water.

The marine hatchet fishes are small, ugly deep sea fishes. They have enormous eyes and flashing light organs along their sides. They hang motionless in the water and do not do much normal swimming. Instead they migrate to and from the surface each night to feed on plankton.

The freshwater hatchet fishes come from South America. They are said to be the only fishes that can truly fly. They leap from the water and propel themselves through the air for short distances by beating their enlarged pectoral fins.