Quantitative analysis of the optic nerve of minnows using light- and electron microscopy demonstrated that anatomical characteristics of the visual system are closely related to habitat turbidity. Species in the genera Notropis and Cyprinella inhabiting predominantly clear water had larger eyes and almost twice as many optic nerve fibers compared to minnows of turbid habitats. No differences were detected in the thickness of myelination, the axon diameter profile, or the number of optic nerve fibers per retinal area, indicating that the relative number of fibers, as well as their anatomical characteristics, are similar in all species and independent of habitat turbidity. It is therefore hypothesized that quantitative differences in the number of visual elements available for sampling and processing in the retina, optic nerve, and optic tectum are sufficient to account for presumed differences in visual performance.

Keywords:
Neuroanatomy, Retina, Optic nerve, Vision, Electron microscopy, Functional adaptation, Environmental plasticity, Fishes, Cyprinidae, Teleost
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© 1992 S. Karger AG, Basel
1992
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