Is the perception of their own odour effective in orienting the exploratory activity of cave fishes?

Spatial knowledge of the surrounding environment is extremely important for animals to locate and efficiently exploit available resources (e.g., food, shelters, mates). Fishes usually acquire spatial information about their home range through vision, but vision fails in the dark and other sensory pathways have to be exploited. Fishes possess a remarkable olfactory system and have evolved a refined ability of chemical detection and recognition. Nevertheless, while the role of chemical cues in spatial orientation is well known in long-distance salmonid migrations, it has never been investigated in orientation within local, familiar areas. Here we report the first evidence that fish swimming can be topographically polarized by self-odour perception. When an unfamiliar area was experimentally scented with fish self-odour, the cave cyprinid Phreatichthys andruzzii Vinciguerra, 1924 behaved as if the area was previously explored. The fish preferred an odour-free area to a self-odour-scented one, and when offered the choice between a familiar and an unfamiliar area, they preferred the unexplored environment. Avoidance of self-odour-scented areas would allow effective exploration of the subterranean environment, minimizing the risks of repeatedly exploring the same water volumes. Our results are the first clear evidence that fish can use their own odour to orient their locomotor activity when visual cues are not available. This highlights the possible role of chemical information in fish orientation.