In young zebrafish the proportion of myelinated axons and myelin thickness is fully restored after demyelination. (A) In lesioned optic nerve, electron microscopic analysis shows many demyelinated axons at 8 dpl (asterisks) and complete remyelination at 28 dpl compared to unlesioned controls. (B) At 8 dpl the number of myelinated axons in the lesion area is significantly reduced compared to unlesioned controls (p < 0.05, n = 3 fish, Kruskal Wallis test, Dunn’s post-test), while there is no difference between remyelinated and control optic nerves. (C) Graphs of G-ratio versus axon diameter show similar patterns at 28 dpl and in unlesioned controls, while most axons at 8 dpl have a higher G-ratio (less myelin). (D) Average G-ratio between unlesioned and remyelinated optic nerve is not different, indicating remyelination with normal thickness myelin (p > 0.05, n = 3-6 fish, Mann Whitney U-test). Mean ± SEM. Scale bar: A = 1 μm.