Dominance and individual recognition in Potamon fluviatile (Decapoda, Brachyura): possible role of visual cues.

Interchangeable tags were attached onto the carapace of river crabs that were analyzed in trios. After a first fight to determine dominance, the tag of the dominant was attached to the subordinate and vice versa. In the second fight, the beta crab behaved towards the real gamma as an alpha and towards the real alpha as a gamma, which demonstrates the ability of crabs to associate the morphology of the opponents to their rank and to behave accordingly.