Retinal photoreceptor patterning during the larval to juvenile transition in Atlantic halibut (Hippoglossus hippoglossus)

Indirectly developing teleosts, such as flatfishes, have different visual requirements during their larval and juvenile stages. As such, the organization and spectral sensitivity of their retinal photoreceptors differ before and after metamorphosis, yet this transition had not been previously examined. I used Atlantic halibut (Hippoglossus hippoglossus) to characterize the spatiotemporal rearrangement and opsin (photosensitive protein) expression of photoreceptors during metamorphosis. The complex reorganization of the larval photoreceptors shifted the area of greatest visual acuity from the ventrotemporal to the dorsotemporal retina. Genome queries followed by immunohistochemistry experiments respectively examined the opsin repertoire of Atlantic halibut, and the distribution of short- and long-wavelength sensitive opsins during this developmental transition. These experiments confirmed that the opsin repertoire of Atlantic halibut is consistent with that of other flatfishes and suggest opsin switching as a mechanism to create new photoreceptor phenotypes during metamorphosis.