A Fish’s Eye View of Habitat Change

Abstract

In aquatic ecosystems, visually mediated predator-prey interactions are highly dependent on the environmental light regime; however, the wavelengths of ambient light and thresholds of light intensity vary as a function of water depth and dissolved organic matter. Light is also scattered by water molecules creating polarized light and by silts and clays creating turbid conditions. As a result of these changes in the visual environment, the visual systems of fishes have developed many adaptations, and are finely tuned to the spectrum and intensity of light in the microhabitat. In addition to these physical constraints, natural selection favors prey that are harder to detect by the predator. To improve the probability of detecting these cryptic prey, many planktivorous fish utilize “saltatory search”, a behavior which is intermediate between ambush and cruise search strategies. Foragers using a saltatory search strategy only search during stationary pauses between repositioning movements. To further improve their foraging success, these fish systematically change the components of search in response to changes in the prey assemblage and light environment. Variation in environmental light is a selective pressure for changes in foraging behavior, but also leads to changes in the fish eye. The structure of the eye, retinal organization and visual pigments of fish all vary as a function of ambient light conditions. These visual system variations can be classed as 1 ) reversible, where the fish respond to changes on a daily, seasonal or migratory cycle; or 2) irreversible, where the fish undergo a transformation or metamorphosis in preparation for life in a new habitat. The life history strategy and the light environment of the visual habitat can explain variable timetables of retinal development. The visual habitat of fish is a complex niche varying in the quality and intensity of light. The corresponding diversity revealed in the structure of the visual system in fish is dynamic and intriguing. The visual ecology of fish is directly affected by the environmental light conditions. Vision is very important to foraging success and predator avoidance in fish, which are important selective pressures in the adaptation of the retina/fish eye to visual habitat. Understanding retinal structure and function in the context of behavioral ecology is an area rich for further research.