Urine as a social signal in the mozambique tilapia (Oreochromis mossambicus).

Despite the high degree of social organization and complex behaviour of many cichlids, little is known about the role of chemical communication in these fish. The Mozambique tilapia is a maternal mouth-brooding cichlid; territorial males congregate in leks and are actively sought by ripe females. When approached by a female, males display a range of well-characterized behaviours such as nestdigging, trembling and circling the female (Baerends and Baerends van Roon, 1950). The female then chooses a mate, spawns and carries the fertilized eggs away in her mouth to incubate them in solitude. The extent to which olfactory cues participate in this process is unknown. Several species of freshwater fish have been shown to release pheromonal messages via the urine (Stacey and Sorensen, 2002); we have previously shown that female tilapia have high olfactory sensitivity to the urine of male conspecifics (Frade et al., 2002). In order to test whether this species is actively signalling to conspecifics or the olfactory sensitivity evolved as a form of chemical spying (Sorensen and Stacey, 1999), the current study assessed changes in urination rates of both sexes in different social contexts.