Fish exchange by "booing"

Image credit: Dario Bayani

Some of the communication signals used by animals are well known, such as birds singing and lions roaring. But there are also some animals that take them by surprise and use a variety of "strange" codes. Researchers recently discovered that a species of cichlid uses urine to deliver chemical signals to opponents during competition.

The researchers used transparent separators to separate large and small fish. Half of the divider contains small holes that allow water to flow back and forth. The scientists then injected the fish with purple pigment to dye their urine blue. When these fish see each other, they raise their fins and swim hurriedly toward the separator. They also change the way they urinate. Fish separated by solid obstacles cannot detect their opponent's urine.

In order to get the message out, the fish began to "boo" more often. Researchers recently reported in Behavioral Ecology and Biosocials that smaller fish are trying to attack larger adversaries because they don't get chemical cues in their urine.

The researchers speculate that humans may also be missing out on some other natural signals. In addition to chemical signals, animals use seismic vibrations, electric currents, and ultraviolet light for communication. While visual signals may be more pronounced, the study also highlights the importance of looking for less obvious forms of communication used by organisms.