Vision in fishes layers of other neurons before it reaches them. The retina contains rod cells and cone cells. Within the retina, rod cells provide high visual sensitivity (at the cost of acuity), being used in low light conditions. Cone cells provide higher spatial and temporal resolution than rods can, and allow for the possibility of colour vision by comparing absorbances across different types of cones which are more sensitive to different wavelengths. The ratio of rods to cones depends on the ecology of the fish species concerned, "e.g.", those mainly active during the day in clear waters will have more cones than
Retina the retina, which in its entirety comprises ten distinct layers, including an outer layer of pigmented epithelial cells. The only neural cells that are directly sensitive to light are the photoreceptor cells, which are of two types: rods and cones. Rods function mainly in dim light and provide black-and-white vision while cones are responsible for the perception of colour. A third type of photoreceptor, the photosensitive ganglion cells, is important for entrainment and reflexive responses to the brightness of light. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses that are sent