Interesting info on fish vision
here...
Oops, that's just deep water...
Here's better info:
"How do fish see ?
The optical system in fish is similar to that of land vertebrates. However, there are some important differences. They have spherical-shaped lens, and they focus by changing the relative distance between the lens and the retina.
Many deep-sea fish have mostly rods for increased low light sensitivity. They even have epithelial layers for protection from bright light.
Fish with cones have 4 types- red, green, blue, and ultraviolet (some have 2 or 3). Fish with all 4 cones live close to water surface...Some fish have upwardly directed eyes- specially those which are preyed upon by birds.
Some fish have tubular eyes, which help to concentrate the limited light that penetrates to great depths.
The south American “four-eyed fish” swims along the surface, with its eyes protruding partly out of the water. Each of its two eyes is split into an upper half for vision in the air and a lower half for underwater vision."
From this