You race against the Hatchetfish Ax in the game.

Here is a shortened version of  seasky.org ‘s article on the Hatchetfish:

The deep sea Hatchetfish gets its name from the shape of its body. They are most well known for their extremely thin bodies which really do resemble the blade of a hatchet. Most of the smaller hatchetfish species are covered in delicate silvery scales. Hatchetfishes have large, tubular eyes that pointing upward. This enables them to search for food falling from the above. Because there is very little light at the great depths at which they are found, their eyes have become extremely sensitive to light and are good at distinguishing shadows against the extremely faint illumination from above.

Hatchetfishes are one of the many deep sea creatures that have the ability to create their own light through a process known as bioluminescence. These fish have special light-producing organs known as photophores that run along the length of their body. These photophores produce light by means of a chemical reaction similar to that of the land-based firefly. Since these light organs point downward, it is believed they are used to hide the fish from predators through the process of counterillumination. This means that they can adjust the intensity of their underside lights to make them nearly invisible against the faint light above.

Not much is known about the life cycle of hatchetfishes. Most researchers agree that they have a short life span of no longer than a year. It is believed that they migrate to shallower waters at night to feed mainly on plankton and tiny fish. They hunt by looking for the silhouettes of their prey moving overhead. At day break, they return to the blackness of the deep ocean. Most of their reproductive habits are a mystery, although it is known that the juveniles look much different that the adults.  (Source: http://www.seasky.org/deep-sea/hatchetfish.html)

Other websites about Hatchetfish:

http://en.wikipedia.org/wiki/Marine_hatchetfish