Environmental Biology of Fishes 59: 21–28, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. Ontogeny of spectral transmission in the eye of the tropical damselfish, Dascyllus albisella (Pomacentridae), and possible effects on UV vision George S. Losey a , Peter A. Nelson & Jill P. Zamzow Hawai’i Institute of Marine Biology and Department of Zoology, University of Hawai’i, P.O. Box 1346, Coconut Island, Kane’ohe, HI 96744-1346, U.S.A. (e-mail: losey@hawaii.edu) a Senior author Received 26 November 1999 Accepted 21 March 2000 Key words: ultraviolet, UV-blocker, fish, MAA, lens, cornea Synopsis The visual ecology of fishes places changing demands on their visual system during development. Study of changes in the eye can suggest possible changes in behavioral ecology. The spectral transmission of the pre-retinal ocular media controls the wavelength of light that reaches the retina and is a simply measured indication of their potential visual capabilities. Dascyllus albisella is a coral reef planktivore known to have UV-sensitive retinal cone cells. UV vision probably aids in detection of zooplankton. As a juvenile it is very closely associated with branching coral heads or, more rarely, sea anemones. As it matures, it ventures farther from its coral, above the reef, and eventually assumes a more vagile life style, moving farther and more frequently afield. Their eyes contain short-wavelength blocking compounds in the lens, cornea and humors. As they age, both the lens and the cornea accumulate blocking compounds that increase the 50% transmission cutoff of the whole eye from ca. 330 nm in 2–3 cm juveniles to ca. 360 nm in the largest adults. The cornea increases its cutoff wavelength faster than the lens and becomes the primary filter in large adults. The cutoff of the aqueous and vitreous humors combined does not change with size. The slope of the transmission cutoff curve increases with the size of the fish. The increased blocking of UV radiation is likely not an adaptation to protect the eye from short-wavelength induced damage. Instead it probably reduces the image degradation effects of short-wavelength light in the largest eyes and still allows sufficient penetration of UV radiation to permit functional UV vision. Introduction The vertebrate eye changes markedly with age (Douglas & Marshall 1999). These changes include passive filtration of light before it reaches the retina and changes in the neurosensory cells. Description of changes in neurosensory function involves demanding physiological studies that are beyond the capabilities of most behavioral laboratories. Much, however, can be learned from study of the passive transmission of the eye that can be accomplished with minimal instrumen- tation. If most of the radiation of a certain wavelength is blocked prior to reaching the retina, visual stimuli of corresponding wavelength are likely of little use to the animal. In addition, changes in filtration with age or environment can serve as clues to changes in selection pressure. Most attention has been devoted to lenticular fil- tration of short-wavelength light. Fishes, in particular, demonstrate a variety of changes in the filtration prop- erties of the lens with aging. Increase in the diameter of the lens alone will block a larger proportion of the lower UVA radiation without the addition of any special UV blockers (Douglas 1989, Thorpe & Douglas 1993). As a fish grows, however, it is very common to accumulate short-wavelength-blocking compounds in its lens. This may result in a visibly yellow lens with a 50% transmis- sion cutoff lower than 425–450nm or, if the blockers