Fish come in all shapes and sizes, from pretty standard-looking minnows to ocean sunfish, or electric eels. Still, every so often I stumble across a fish that is so strange looking I have to do a double-take. Today’s animal, the common hatchetfish, is one of those fish.

Look how strange he looks! Image by Oregon State University, CC BY-SA 2.0, via Wikimedia Commons

Common hatchetfish are freshwater fish found in the Amazon River and its tributaries. They prefer to stay near the surface of the river, and generally hide in vegetation by the rivers’ banks. Hatchetfish will school, and only when they have the protection of their friends will they venture into open river waters.

Hatchetfish don’t get to be very big, reaching maximum lengths of 6.5 cm. They have extremely strangely shaped bodies, that are laterally compressed with a huge abdomen. This area houses the hatchetfish’s pectoral muscles, which can make up 25% of the fish’s body weight.

These muscles are used to power the hatchetfish’s wing-like pectoral fins. When hatchetfish are in danger, they will use these fins to jump out of the water, and ‘fly’ for a few meters before dropping back into the water. Hatchetfish will also spring from the water to catch flying insects, though they will eat insects that fall into the river as well. Hatchetfish are unique in that they actually use their fins to aid in flight, flapping them like birds’ wings.

Likely due to their funny shape, hatchetfish are popular aquarium fish. They do fairly well in captivity, but care must be taken to have a well-secured lid on the tank, as the fish will jump out of the water when startled. I know fish leaping out of a tank would scare the hell out of me, so I definitely wouldn’t want to keep any hatchetfish around.

Cover image by Neale Monks at the English language Wikipedia, CC BY-SA 3.0, via Wikimedia Commons