Subterranean Fishes of the World

943

1957

Experientia

394

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As previously reported, the Characinid Astyanax, a normal eyed and dark pigmented fish which lives in overground waters, can be crossed with the pigmentless or feebly pigmented blind cave fish Anoptichthys which is accepted to be its descendant or close relative. The F 1 hybrids are fertile. Anoptichthys is found in different populations which were described as different species and which are genotypically different from one another. In the F 2 generations of both Sabinos and Chica cave fish with normal river fish, recombination of the genes which are responsible for pigmentation and those for eye structure, is observed on a polygenic basis. The number of degenerative genes found in the Sabinos population which lives in the inner part of the cave system, are greater in number than those observed in the Chica population which is located nearer the overground river, Rio Tampaon. The Pachon population found at the innermost cave has even more degenerative genes than the Sabinos fish. The Pachon cave fish used as a grandparent to produce a F2 generation was captured in nature some years ago. It carried, besides many other genes for pigment reduction, agene which in homozygous condition p r e v e n t s pigment formation even in the eyes. The F2 generation, which results from the cross between Pachon and the overground river fish resulted in 26% (278) albinotic individuals having unpigmented, red eyes of the most different degrees of development from practically none to ± normal. The body of these albino fish is completely pigmentless. The remaining 74% (787) of the F, individuals have dark eye pigment even when their eyes are of the most rudimentary type. The body colour of these non-albinotic individuals shows a series of gradations between the body colour of normally pigmented i n d i v i d u a l s and that typical for cave fish, the pigmentation of which has been much reduced. Thus, in these 74%, the number of polymeric genes present in each of the F, fishes controls the degree of melanophore formation. On the other hand, in the albinotic individuals the formation of pigment does not take place, because of the presence of an epistatic inhibitory gone pair. It is very interesting to note that such a great mutational step causing the extinction of all the melanine which up to now is known only in domesticated fish (Salmo irideus, Xiphophorus helleri, Mollienisia 'sphenops', Derrnogenys pusillus et al.), could be found in cave fishes under absolutely natural conditions.

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