Question

Hi, this is bugging me currently , how far can a fish see in water , given perfectly clear water .

Answer 1

Most fish can see distances based on that distant objects color. As in people, the retina of a fish's eye contains two types of cells, rods and cones. Cones are used for day vision and are the cells used to see colors. Rods are used for night vision and cannot distinguish colors, although they can judge light intensity. The eyes of most freshwater fish contain both rods and cones, though day feeders tend to have more cones, and night feeders more rods.

In theory, rainbow trout and Pacific salmon have color vision similar to that of humans. All other fishes can clearly see different colors and the shape associated with it at different distances.

But light behaves differently in water than it does in air. The various colors of light travel at different wavelengths. The longest wavelengths are the reds, followed by oranges, yellows, greens, blues, indigos, and violets. When light travels through water, some of its energy is absorped, and the longest wavelengths are the ones absorbed first. Thus, the warmer colors fade out and gradually appear black as light penetrates the water column. Red light is almost completely absorbed within the first 15-20 feet. Orange penetrates to 30-40 feet, and yellow to 60-70 feet, while green and blue remain visible for as deep as the light penetrates.

Thats how the fishes eyesight can distinguish also.
There you go:)