At least one species of fish communicates aggression using chemicals found in its urine, scientists in Switzerland have discovered in an experiment to uncover behavioral habits.
Researchers at the University of Bern conducted experiments on the cichlid fish of various sizes and studied how they interpreted urine signals to convey aggressive or submissive behavior.
Scientists already believed that fish urinated in moments of aggression, but up to this point it had not been known that urine is used as a behavioral signal.
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The study, published in the Behavioural Ecology and Sociobiology journal, involved tanks being set up with a partition between the fish to prevent physical interactions and then adjusted for the experiments.
It was discovered that the frequency of urination was significantly higher when two fish could see each other but were separated within a tank, apparently aware that their message was not being received.
Fish displayed aggressive actions but, when chemicals were successfully transmitted, the smaller fish reduced its aggressiveness, surrendering to the larger one.
Fish were injected with a violet blue dye to allow the volume of urine expelled to be seen and measured, and then pairs were subject to a series of scenarios of varying visual and chemical contact.
Other animals use chemical cues to communicate for various reasons, from bonding and mating to territorial and social ranking markings.