Mean thickness of the different retinal layers in Clarias gariepinus. Each column represents the mean value ± SD (n = 7); * significant at p < 0.05. (NL) Normal light, (BL) bright light, (DL) dim light, (GCL) ganglion cell layer, (IPL) inner plexiform layer, (INL) inner nuclear layer, (OPL) outer plexiform layer, (ONL) outer nuclear layer, (PR) photoreceptors, (PE) pigmented epithelium.