Axons from the eye normally project to the opposite side of the fish brain. In the belladonna mutant, retinal axons project to the ipsilateral tectal lobe and no optic chiasm forms. The response to visual cues (motion) in these fish is reversed.
The fluorescent lipophilic dyes DiI and DiO were regionally injected into the left eye of a fixed 5 day zebrafish larvae. Dye taken up by retinal ganglion cells in the eye diffused throughout the cellular membrane, labeling the axons that contribute to the optic nerve and tract and terminating in the visual center in the brain, the optic tectum. Retinal axons project topographically in this target region: anterior retinal cells (green) project to the posterior region of the tectum while posterior retinal cells (red) project to the anterior region.