Image: Wikimedia Commons/Tino Strauss 
 
 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. 
 
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 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 anesthetized 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 Behavioral 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. 
 
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 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. 
 
 I don’t have any concluding thoughts here. Scientists observed fish have pissing contests. Incredible. 
 
 [Behavioral Ecology and Sociobiology via Science] 

 Some of the signals animals use to communicate are obvious. Birds sing. Lions roar. But there’s a whole category of signals in the natural world that humans rarely notice. Researchers have found that one species of cichlid uses urine to send chemical signals to rivals during aggressive displays. The team separated large fish from small fish with a transparent divider. Half the dividers contained holes to allow water to flow back and forth. The scientists then injected the fish with a violet dye (pictured), turning their urine bright blue. When the animals saw each other, they raised their fins and rushed toward the divider. They also changed the way they peed. Fish separated by a solid barrier couldn’t detect their opponent’s urine. In an attempt to get their message across, they urinated even more. Without the chemical cues provided by the urine, smaller fish often tried to attack their larger opponents, the team reports this month in Behavioral Ecology and Sociobiology . Humans could be missing other signals as well, the researchers contend. In addition to chemical signals, animals use seismic vibrations, electricity, and ultraviolet light to communicate. Visual signals might be more obvious, but this research stresses the importance of looking for less noticeable forms of communication, the authors say.
– Perhaps you know someone who's written his name in snow, you know, with urine. That's essentially what some fish do every day. In a study titled, "To pee or not to pee: urine signals mediate aggressive interactions in the cooperatively breeding cichlid," researchers explain that urination for the cichlid fish is not only a bodily function but also a form of communication, per Science. To figure that out, they injected the fish with a dye that turned urine blue, then measured a fish's urine while it was kept separate from other fish. Researchers then placed a larger cichlid and a smaller cichlid in the same tank, separated by a transparent barrier. When the fish spotted each other, they swam toward the barrier in an aggressive manner with fins raised and peed. Researchers say the fish clearly used their fins to communicate visually. But the fish also gave off a chemical signal with urine. In cases where the barrier had tiny holes allowing water to flow through, for example, the smaller fish appeared to get a signal from the larger fish to stop their attack since they were more likely to show aggression when the barrier was solid. Both the smaller and larger fish also peed more when presented with another fish than they did when alone, especially when the barrier between them kept them from receiving the other fish's signals. Researchers are only beginning to understand this form of communication, but Gizmodo sums it up thusly: "Fish literally have pissing contests." (Big and small mammals take the same amount of time to pee.)