Microscopic observation of the retinal photoreceptor layer of the common barbel (Teleostei: Cyprinidae)

Light and electron microscopic observations show that cones-belonging to four types are present in the retina of the common barbel Barbus barbus (L.): short single cones, long single cones, twin cones, and unequal double cones. They do not exhibit any particular arrangement. Estimates of cone density suggest that the common barbel has multichromatic vision but of low acuity and that no difference exists between the lower and the upper parts of the retina. Both cone density (approximately 3000 units/mm(2)) and the proportion of double cones to single cones (approximately 1:3) are low. The view that the barbel has an inferior colour vision is in good agreement with the fact that this species is active mainly at twilight, but with diurnal activity during spawning.