How do trout eyes detect dim light and distinguish colour?

Trout, like other protacanthopterygians, possess well-developed eyes that rely on two primary types of photoreceptor cells in the retina to process visual information.1

• Dim Light Vision: Trout utilize rods, which are highly sensitive to low levels of illumination, to facilitate vision in dim light. When light strikes these cells, it triggers a chemical change in visual pigments—such as rhodopsin—that stimulates the receptor nerves to produce a visual signal.1234
• Colour Vision: Trout distinguish colour through the use of cones. These photoreceptors are associated with colour perception and the ability to perceive fine detail. The process involves a complex system of colour-coding where different types of cones respond to specific regions of the light spectrum. This information is transmitted to horizontal cells in the retina, which organize these signals into opponent responses (such as red-green or blue-yellow), allowing the fish to effectively emphasize and distinguish colour differences in their environment.124