Assessment of a novel color vision optomotor response assay in zebrafish larvae with red cone ablation

Zebrafish are widely used to investigate visual function, owing to their well-defined retinal organization and optical transparency during early developmental stages. Here, we evaluate the effectiveness of a color vision optomotor response (CV-OMR) assay for assessing zebrafish with red cone ablation. Tg (thrb:gal4;UAS:epNTR-p2a-mCherry) transgenic zebrafish were used to ablate red cones via the addition of metronidazole (MTZ). Transgenic zebrafish larvae were treated with MTZ for 0, 12 and 24 h at 5 days post-fertilization, resulting in Tg(+)MTZ(-), Tg(+)MTZ(+)12 h and Tg(+)MTZ(+)24 h groups, respectively. The areas of mCherry-expressing cells, representing red cones in tissue sections, were compared. The mean mCherry expression area was smallest in the Tg(+)MTZ(+)24 h group (16.5 ± 7.6 μm²), followed by the Tg(+)MTZ(+)12 h (404.1 ± 200.9 μm²) and Tg(+)MTZ(-) groups (1,066.6 ± 252.2 μm²; P < 0.001). At 6 days post-fertilization, zebrafish larvae were evaluated using the CV-OMR assay comprising two colors. Results were reported as the area under the curve of the ratio of larvae at the starting point curve. The ratio of larvae at the starting point decreased most rapidly in the Tg(+)MTZ(-) group and most slowly in the Tg(+)MTZ(+)24 h group. There were significant differences in the area under the curve of the ratio of larvae at the starting point curve among the three groups. In conclusion, the CV-OMR assay demonstrated the ability to differentiate color vision impairment based on the extent of red cone ablation. The CV-OMR assay used in this study may prove valuable for evaluating color vision in zebrafish with various eye diseases.