A fish brain is small, and almost all of it is used to control vision. Vision is critically needed for hunting food. The olfactory bulb is well developed too, allowing fish to smell chemicals dissolved in water.

Fish see the world different from you. A trout’s eyes can focus from a few inches to infinity, in a narrow arc of vision, in front of and slightly above their head. They have a 180-degree field of vision., and their eyes move independent of one another.

Thus, the fish can employ its binocular vision to focus on prey approaching from the front, while retaining distance focus in the backward, downward, upward, and lateral directions. This allows the trout to detect and focus on its prey and simultaneously spot approaching predators.