The visual ecology of Holocentridae, a nocturnal coral reef fish family with a deep-sea-like multibank retina.

The visual systems of teleost fishes usually match their habitats and lifestyles. Since coral reefs are bright and colourful environments, the visual systems of their diurnal inhabitants have been more extensively studied than those of nocturnal species. In order to fill this knowledge gap, we conducted a detailed investigation of the visual system of the nocturnal reef fish family Holocentridae.

Cardinalfishes (Apogonidae) show visual system adaptations typical of nocturnally and diurnally active fish.

Animal visual systems adapt to environmental light on various timescales. In scotopic conditions, evolutionary time-scale adaptations include spectral tuning to a narrower light spectrum, loss (or inactivation) of visual genes, and pure-rod or rod-dominated retinas. Some fishes inhabiting shallow coral reefs may show activity during the day and at night.

Short-term colour vision plasticity on the reef: changes in opsin expression under varying light conditions differ between ecologically distinct fish species.

Vision mediates important behavioural tasks such as mate choice, escape from predators and foraging. In fish, photoreceptors are generally tuned to specific visual tasks and/or to their light environment, according to depth or water colour to ensure optimal performance. Evolutionary mechanisms acting on genes encoding opsin, the protein component of the photopigment, can influence the spectral sensitivity of photoreceptors.