Pissed-off Fish: Urine Signalling to indicate aggression in the Neolamprologus Pulcher Cichlid
From an anthropocentric point of view, animals most commonly communicate in either aural or visual ways, such as dogs barking or peacocks having elaborate mating displays. However, one mode of communication oft overlooked is chemical, due to its less visible, and by extension observable, nature. One way in which animals can communicate chemically is through urinating, which mice, cats and dogs often do to mark out their territories, which leads to improved male reproductive success.
However, a recent study published in Behavioral Ecology and Sociobiology has shown that cichlids called the Neolamprologus Pulcher utilize urination to communicate with one another. More specifically, it has been found that these cichlids urinate to indicate aggressive behaviour.
So How Did They Find Out?
A number of tanks were set up, each with a partition between a large and small fish (which had a minimum difference in size of 9 mm) to prevent physical interaction. The properties of the partition in each tank were varied, with some having pores that allowed water (and by extension urine) to pass through to the other side. Both fish were then injected with a violet blue dye to allow the volume of urine expelled to be visible in order for urine pulses to be counted.
It was discovered that the frequency of urination for both fish was significantly higher when two fish could see each other as compared to when they could not. When chemical signals were not able to go through the non-porous transparent partitions, both fish emitted more urine in a possible attempt to remedy the problem of their message not getting through.
Furthermore, when chemicals were successfully transmitted through the porous partition, the smaller fish reduced its aggressiveness and surrendered to the larger one. This suggests that the smaller fish would need to detect the chemical signal found in the big fish’s urine before being able to respond to it; size alone is not enough to scare away the small fish.
One of the main takeaways from this study is the importance of “studying multimodal signals” (i.e. signals beyond the sights and sounds) when animals interact if we are to attain a better understanding of animal interaction and communication.