Regulation of eye growth in the African cichlid fish Haplochromis burtoni.

Fish were reared in 6 conditions: broad spectrum white light, total darkness, scotopic illumination, and 3 monochromatic colors matched to the absorption spectra of the three cone types to study the influence of the light regime on the regulation of eye growth in the African cichlid fish Haplochromis burtoni. Fish reared in total darkness showed high variability in naso-temporal diameter and axial length of the eye. Animals reared in darkness and in scotopic illumination had significantly larger eyes relative to lens size in comparison to fish reared in white light. Eye size and shape was nearly identical in fish reared in monochromatic and in white light. Because of overlap in the absorption spectra of the three cone types of H. burtoni it could not be resolved whether the regulatory mechanism receives input from all three cone types or only from the green (523 nm) sensitive cones. It is clear from our results, however, that neither the blue (455 nm) nor the yellow sensitive (562 nm) cones alone are responsible for eye size regulation. It seems equally unlikely that all three cone types have to act in concert for normal growth of the eye.