Male cichlids pee to communicate, according to a study by Karen Maruska and Russell Fernald published in a recent issue of the Journal of Experimental Biology.
Studying dominant male Astatotilapia burtoni, the authors tested the hypothesis that the males were using chemical signals in urine during interactions with females and other males.
The authors injected 40 male cichlids with a blue dye to make the urine pulses visible, and then subjected each male cichlid to one of four different treatments, each repeated ten times.
The four treatments were the introductions into the same tank of: (1) another dominant male; (2) two mouthbrooding females; (3) a gravid female or (4) no fish (as a control).
The authors found that the male cichlids urinated more frequently in the presence of the gravid female compared to exposures to mouthbrooding females or no fish.
They also found that the male cichlids also urinated more frequently in the presence of another dominant male, suggesting that chemical signals in the urine may convey information on dominance status.
They repeated the experiment, this time exposing the test fish to only visual cues (ie. the fish were only able to see the treatment fish through a transparent barrier), and obtained similar results, although they found the urination frequency to be significantly lower when the test fish were only allowed to use visual cues compared to the situation where they were allowed to use all sensory information.
For more information, see the paper: Maruska, KP and RD Fernald (2012) Contextual chemosensory urine signaling in an African cichlid fish. Journal of Experimental Biology 215, pp. 68–74.
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