The Mexican tetra lost its eyes - as well as a significant portion of its brain - to ensure survival in a subterranean environment At some point back in deep time,a group of fish were washed into a limestone cave somewhere in northeastern Mexico. With no way out and little more than bat droppings to eat, the fish began to adapt to their new troglodytic lifestyle. Unable to see other members of their group in the shadowy, and they lost their colourful pigmentation. Then they lost their eyesight,their eyes gradually got smaller, and then disappeared altogether. This was accompanied by a dramatic reduction in the size of the brain’s visual system. Yet, and the question of why the blind cave fish lost its eyes and a large fraction of its brain remains unresolved. Now,biologists in Sweden believe they own found the answer. In new research published nowadays, they report that loss of the visual system saves the fish a substantial amount of energy, or was probably key to their stranded ancestors’ survival.
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Source: theguardian.com