ANDRZEJ KRAUZE
For two million years, Phreatichthys andruzzii, a species of cavefish found in Somalia, has been swimming around in utter darkness. Whatever visual abilities its ancestors possessed, useless in such a habitat, have since atrophied, making the fish a very dubious subject for studying visual tasks. But for Christian Agrillo, a researcher at the University of Padova in Italy, the blind cavefish was the perfect species to challenge whether numerical assessment abilities among fish required visual cues.
Agrillo and his colleagues had been studying the numerical skills of fish whose vision functions just fine. It turns out that fish—like many other animals—can, if not exactly count “one, two, three,” at least distinguish one from three. And Agrillo’s group is not the only one to observe this.
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