Various procedures have been adopted to investigate spectral sensitivity of animals, e.g., absorption spectra of visual pigments, electroretinography, optokinetic response, optomotor response (OMR), and phototaxis. These works have led to various conclusions about animal vision. However, visual sensitivity should be evaluated consistently for a reliable comparison. In this study, we retrieved behavioural data of several fish species that used a unified procedure for the OMR test and compared the sensitivities to near-infrared light. Besides cavefish that lack eyes, some species were not appropriate for the OMR test because they either stayed still or changed swimming direction frequently. Eight fish species out of 13 species tested were OMR positive. Detailed analyses using goldfish, zebrafish, guppy, medaka, stickleback, and cichlid revealed that all the fish were sensitive to light at λ ≥ 750 nm, where the threshold wavelengths varied from 750 nm to 880 nm. Fish opsin repertoire enabled the perception of red light. In contrast, the copy number of long-wave-sensitive (LWS) genes did not necessarily improve red-light sensitivity. The duplication of LWS and other cone opsin genes that have occurred extensively during fish evolution might not aid increasing spectral sensitivity, but provide some other ophthalmic function, such as enhanced spectral discrimination.

Fig3 OMR data sets of Nile tilapia under light of 720, 750, 800, 810, 820, 830, 840, 850 and 860nm. OMR data sets of Mexican cavefish under light of 720, 750, 800, 820 and 860 nm. Fig3.zip Fig4 OMR data sets of medaka, goldfish, zebrafish, guppy, three-spined stickleback, mbuna under light of 700, 750, 800, 850, 900, 950 and 1000 nm. Fig4.zip Fig5 OMR data sets of medaka, goldfish, zebrafish, guppy, three-spined stickleback, mbuna under light of 780, 800, 820, 840, 860 and 880 nm. Fig5.zip OMR data sets of goldfish for Steel's test OMR data sets of goldfish under light of 780, 800, 820, 840, 860, 880 and 950 nm. SteelsComparison_Goldfish.zip ND: not determined, NA: data not available (fish did not show positive OMR)