Ultraviolet photosensitivity in goldfish: an independent u.v. retinal mechanism.

Heart rate conditioned goldfish were sensitive to u.v. stimuli at wavelengths down to 340 nm. A u.v. peak had maximum sensitivity at about 380 nm and was depressed selectively by a u.v. adapting background. An opaque cone restricted light to the eye, reducing the probability of a dermal or pineal gland source of the response. Three experiments demonstrated a retinal origin for the u.v. peak. The conditioned response to u.v. stimuli was abolished following injection of Lidocaine into the eye. U.V. sensitivity remained when the cornea, iris and lens were extirpated. Finally, the u.v. peak showed an orderly change in sensitivity with alteration in adapting u.v. illumination.