title: Functional changes of the visual system of the damselfish Dascyllus marginatus along its bathymetric range.
abstract: Shallow-water zooplanktivorous fish rely on their vision for foraging. In shallow water, feeding efficiency decreases in dim light and thus the fish cease foraging at crepuscular hours. Creatures living in the lower parts of their depth ranges are expected to be exposed to limited light levels for longer hours. However, observations of the zooplanktivore Dascyllus marginatus showed little change in foraging duration down to 40m deep. We asked whether the visual system's functionality changes with depth along the depth range of this damselfish; we examined eye and retina anatomy for changes in visual acuity and light sensitivity and used the optomotor response to test for spatial and temporal light summation. We found only minor changes in the anatomy of the eye that are not expected to affect visual sensitivity or acuity. However, behavioural experiments showed that the deeper water fish's test performance exceeded those of fish in shallow water under lower light levels. We found that deeper water fish responded to the optomotor test at lower light levels and also had more discriminating visual acuity in low light, which can increase their potential reactive distance. The plastic adaptive ability of the visual system to low light levels may explain the fish's ability to inhabit deeper reef habitats and thus expand their depth range limits.
authors.affiliation: The Interuniversity Institute for Marine Sciences at Eilat (IUI), P.O. Box 469, Eilat 88103, Israel. eran.brokovich@mail.huji.ac.il
authors.forename: Eran
authors.initials: E
authors.lastname: Brokovich
authors.forename: Tomer
authors.initials: T
authors.lastname: Ben-Ari
authors.forename: Salit
authors.initials: S
authors.lastname: Kark
authors.forename: Moshe
authors.initials: M
authors.lastname: Kiflawi
authors.forename: Gal
authors.initials: G
authors.lastname: Dishon
authors.forename: David
authors.initials: D
authors.lastname: Iluz
authors.forename: Nadav
authors.initials: N
authors.lastname: Shashar
mesh_terms: D000221:Adaptation, Ocular / Q000502:physiology*; D000222:Adaptation, Physiological; D000818:Animals; D023681:Cichlids / Q000033:anatomy & histology* / Q000502:physiology; D004192:Discrimination, Psychological / Q000502:physiology; D004777:Environment; D005123:Eye / Q000033:anatomy & histology*; D005247:Feeding Behavior / Q000502:physiology*; D011235:Predatory Behavior / Q000502:physiology; D012160:Retina / Q000166:cytology* / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology