Vision and photoentrainment in fishes: the effects of natural and anthropogenic perturbation.

Vision and photoentrainment in fishes are vital for feeding, avoiding predation, spatial orientation, navigation, social communication and the synchronization of many homeostatic functions such as activity patterns and sleep. The camera-like (image-forming) eyes of fishes are optimized to provide a clear view of their preferred ecological niche, while non-visual photoreceptors provide irradiance detection that mediates circadian photoentrainment, an endogenous time-keeping mechanism (biological clock) to respond to predictable changes in environmental conditions. Fish and fisheries are under pressure from both natural and anthropogenic perturbation, which in many cases alters the intensity and spectral composition of the light environment on which they depend for their survival. This review examines the effects of a changing light environment and turbidity on the health of fishes within a developmental and ecological context. Understanding the sensory environment of fishes is vital to predicting their responses and, ultimately, their resilience to environmental change and the potential for maintaining sustainable levels of biodiversity.