Blind but alive - congenital loss of atoh7 disrupts the visual system of adult zebrafish

Purpose Vision is the predominant sense in most animal species. Loss of vision can be caused by a multitude of factors resulting in anatomical as well as behavioral changes. In mice and zebrafish, atoh7 mutants are completely blind as they fail to generate retinal ganglion cells during development. In contrast to mice, raising blind zebrafish to adulthood is challenging and this important model is currently missing in the field. Here, we report the phenotype of homozygous mutant adult zebrafish atoh7 mutants that have been raised using adjusted feeding and holding conditions. Methods The phenotype of adult mutants was characterized using classical histology and immunohistochemistry as well as optical coherence tomography. In addition, the optokinetic response was characterized. Results Adult atoh7 mutants display dark body pigmentation and significantly reduced body length. They fail to form retinal ganglion cells, the resulting nerve fiber layer as well as the optic nerve, and consequently behave completely blindly. In contrast, increased amounts of other retinal neurons and Müller glia are formed. In addition, the optic tectum is anatomically reduced in size, presumably due to the missing retinal input. Conlusions Taken together, we provide a comprehensive characterization of a completely blind adult zebrafish mutant with focus on retinal and tectal morphology, as a useful model for glaucoma and optic nerve aplasia. ### Competing Interest Statement The authors have declared no competing interest.