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Vision During Growth of a Generalized Haplochromis Species: H. Elegans Trewavas 1933 (Pisces, Cichlidae)

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image of Netherlands Journal of Zoology
For more content, see Archives Néerlandaises de Zoologie (Vol 1-17) and Animal Biology (Vol 53 and onwards).

This study of vision during growth of Haplochromis elegans1 is a functional morphological analysis of the eye as a changing functional component (DULLEMEIJER, 1974). Retinal development is described. Retinal parameters, like densities and distributions of visual cells are determined throughout the span of life of H. elegans. Optical properties of the eye-lens have been measured. A physical model, using ray-tracings, composition of the eye-lens and optical properties of the eye-protein, calculates correctly the chromatic aberration of the eye-lens as a function of lens-radius. Defect of focus of the eye during buccal development is determined. Its influence on resolving power of the eye as an optical instrument is calculated, using diffraction theory. The same theory is used to calculate the influence of chromatic aberration on resolving power as a function of lens-radius. Scotopic vision is analysed numerically, by calculating scotopic retinal visual acuity and convergence during growth. In photopic conditions, the retina appears to be a limiting factor in resolving power from the moment the retina becomes functional (determined by electron-micrographic studies) till the maximum eye-size is reached. The eye-size for which retinal visual acuity is the same as optical visual acuity predicts correctly the maximum eye-size found in H. elegans. The development of the adductor-muscles of the lower jaw is studied and described in relation with the development of vision, which sheds a new light on a kinematical construction and its emergence. A comparison between three haplochromine species of different trophic types demonstrated a variation in photopic and scotopic visual acuity as well as in convergence. The fish feeder has a high convergence and a high scotopic visual acuity. The insect feeder has a high photopic visual acuity. The mollusc feeder has a moderate degree of convergence. A comparison between the eyes of Perca fluviatilis and H. elegans demonstrates that the existence of a yellow cornea in the perch is necessarily connected to the dispersive power of its eye-lens protein.

Affiliations: 1: Department of Morphology, Zoological Laboratory, University of Leiden, The Netherlands


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