Light‐induced acceleration of retina development in a mouth‐brooding teleost

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Abstract
Rearing animals in the dark had been shown to be either without effect on the development of the retina or to result in a reduction or a delay of retinal maturation. In the present study, the influence of light on a retina which normally develops under contitions of very dim light has been investigated. When 3‐day‐old embryos of the mouth‐brooding teleost Tilapia leucosticta are placed into a continuously lighted environment, from day 6 on, optic tract diameter and inner plexiform layer thickness increase up to day 10 or 12. In the dark‐reared retina, this increase occurs only after day 10. Similarly, synaptic junctions of the inner plexiform layer appear at about day 6 in the light‐reared retina and increase continuously on following days, whereas in the retina of embryos reared in darkness, they appear at day 7 and do not increase essenially before day 11. These and other data suggest that continuous light induces a precocious growth of retinal structures. The first differences between light‐ and dark‐reared retinae appear synchronously with the beginning of receptor cell development and prior to the first synaptic junctions. A nonneurally mediated effect of light on the retinal ganglion cells in consequently assumed.