ABSTRACT
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. Results showed that the visual system of holocentrids is well adapted to their nocturnal lifestyle with a rod-dominated retina. Surprisingly, rods in all species were arranged into 6–17 well-defined banks, a feature most commonly found in deep-sea fishes, that may increase the light sensitivity of the eye and/or allow colour discrimination in dim light. Holocentrids also have the potential for dichromatic colour vision during the day with the presence of at least two spectrally different cone types: single cones expressing the blue-sensitive SWS2A gene, and double cones expressing one or two green-sensitive RH2 genes. Some differences were observed between the two subfamilies, with Holocentrinae (squirrelfish) having a slightly more developed photopic visual system than Myripristinae (soldierfish). Moreover, retinal topography of both ganglion cells and cone photoreceptors showed specific patterns for each cell type, likely highlighting different visual demands at different times of the day, such as feeding. Overall, their well-developed scotopic visual systems and the ease of catching and maintaining holocentrids in aquaria, make them ideal models to investigate teleost dim-light vision and more particularly shed light on the function of the multibank retina and its potential for dim-light colour vision.
Footnotes
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: F.d.B., F.C., S.M.S., N.J.M.; Methodology: F.d.B., F.C., S.M.S., M.L.; Validation: F.d.B., F.C., S.M.S.; Formal analysis: F.d.B., F.C., S.M.S., L.F., M.L.; Investigation: F.d.B., F.C., L.F., S.M.S.; M.L., Resources: F.d.B., F.C., S.M.S., N.J.M.; Writing - original draft: F.d.B.; Writing - review & editing: F.d.B., F.C., L.F., S.M.S., M.L., N.J.M.; Visualization: F.d.B., F.C., L.F., S.M.S.; Supervision: F.d.B., N.J.M.; Project administration: F.d.B.; Funding acquisition: F.d.B., N.J.M.
Funding
This research was supported by several Australian Research Council (ARC) grants, an ARC Laureate Fellowship (FL140100197) awarded to N.J.M. and ARC DECRA awarded to F.d.B. (DE180100949) and F.C. (DE200100620). In addition, F.C. was also supported by a University of Queensland Development Fellowship and a Swiss National Science Foundation Early Postdoc Mobility Fellowship and S.M.S. was supported by the German Research Foundation (DFG).
Data availability
Raw-read transcriptomes (PRJNA674704, SAMN16670685–SAMN16670689) and single gene sequences (MW219662-MW219691) are available through GenBank (https://www.ncbi.nlm.nih.gov/genbank/). Gene alignments, phylogenies, transcriptome assemblies, sensitivity prediction alignments and additional tables and figures are available from the Dryad digital repository (de Busserolles et al., 2021): nvx0k6dr3.
Supplementary information
Supplementary information available online at https://jeb.biologists.org/lookup/doi/10.1242/jeb.233098.supplemental
- Received July 23, 2020.
- Accepted November 16, 2020.
- © 2021. Published by The Company of Biologists Ltd
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