The blind cave fish is commonly found in many shops and has been a favourite in the hobby for many years. It exists in various caves in Mexico and has long been known to be the same species as the Mexican tetra, Astyanax mexicanus found above ground. Now a new study by a team of researchers from Portugal, America, and Mexico has shed some light into how they came to be.
It seems that the various underground populations are more closely related to the above ground form than to other populations of blind fish. In other words the blind form has evolved multiple times. A striking example of what is known as convergent evolution. Not only that but a significant amount of cross breeding between the two forms still takes place. The fact that the blind form still persists in spite of a constant influx of genes from the sighted form is evidence for a very strong selection pressure against eyes within the environment of the caves. Blind fish are clearly able to produce more offspring in the caves than are sighted fish.
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