How can hatchet fish see in the dark?

Hatchetfish are small, bioluminescent fish that inhabit the deep ocean. They use their bioluminescent organs to communicate with each other and to attract prey. Hatchetfish also have a unique eye structure that allows them to see in the dark.

Hatchetfish eyes are located on the top of their heads, and they are oriented upwards. This allows them to see objects above them, even in the dark. Hatchetfish eyes are also very large, which gives them a wide field of vision.

In addition to their large eyes, hatchetfish also have a special layer of tissue in their retinas called the tapetum lucidum. The tapetum lucidum is a reflective layer that helps to concentrate light on the photoreceptor cells in the retina. This allows hatchetfish to see in very low light conditions.

Finally, hatchetfish have a special type of photoreceptor cell called the rod cell. Rod cells are very sensitive to light, and they allow hatchetfish to see in very dark conditions.

The combination of large eyes, a tapetum lucidum, and rod cells gives hatchetfish the ability to see in the dark. This is a critical adaptation for these fish, as they live in the deep ocean where there is very little light.