Animals, like humans, communicate in lots of different ways. One of those ways, in animals as in humans, involves urinating on one another.
Well, not right on one another, since the fish are in the water. Scientists at the Institute of Ecology and Evolution of the University of Bern wondered whether cichlids were peeing simply because they had to, or as a means of communicating aggression. It turns out that angry cichlids let out some pee to tell one another they’re pissed. Fish literally have pissing contests.
The first step was to create an experiment to measure when and why the fish were relieving themselves. The researchers built special fish tanks in which two fish are separated by an opaque barrier and a transparent barrier. In some tanks the barriers had holes, and in other tanks they lacked holes. Once the fish were acclimated to the water, the scientists anaesthetised them and injected them with a special dye to help track their pee—this also turned the naturally pink fish blue. Finally, they measured the amount of fish pee and number of pee pulses, removed the opaque barrier, measured the pee, put the barrier back, and measured the pee again.
In all cases, the bigger fish peed more—but more importantly, both fish peed more when they could see each other but couldn’t sense the chemicals in each other’s urine—when the barrier without holes separated them. The scientists thus concluded that pee and its chemicals are important for cichlid communication, and published their incredible results in the journal Behavioural Ecology and Sociobiology last week.
“We show that N. pulcher actively signals aggressive tendencies via altered urination patterns,” the researchers write. “Furthermore, we show that appropriate agonistic responses appear to be dependent on the availability of such chemical information,” meaning the fish had to detect each others’ urine to respond to it.
This isn’t the first time scientists have done a study like this, but they do say that chemical communication between fish is something that needs to continue being studied. I take their word for it.