They live in an environment where keen vision would give them less advantage than a good sense of smell, hearing and maybe even taste. A fish's sense of sight seems almost an evolutionary afterthought, as evidenced by the creatures who live so deep in the sea that no light penetrates there. The design of their eyes forfeits visual clarity and precision for strong neural impressions in low-light conditions.
Fish see colors and can distinguish shapes.
Research has shown that fish are responsive to the color spectrum, and can see many shades of color. Higher-evolved fish such as trout and salmon can see reds and blues better than humans. Scientists have proven that salmonidae can see colors in the infrared and ultraviolet wavelengths that are beyond human perception. Like the human eye, the eye of a trout or salmon essentially works like a camera. Light impulses are modified and focused in the lens, and then transferred to the extremely-sensitive cells of the retina.