Differential attack by a cichlid fish on resident and non-resident fish of another cichlid species

摘要

An algivorous cichlid, Variabilichromis moorii (Vm), defends permanent territories in Lake Tanganyika, Africa. A zoobenthivorous cichlid, Neolamprologus mustax (Nm), spends 60% of daylight hours foraging in Vm territories, from which other zoobenthivorous fishes are chased out and consequently which are much richer in prey animals than areas outside of Vm territories. We conducted a field experiment to examine whether Nm residents and non-residents received different degrees of attacks from Vm. Nm fish were caught in their territories, released at a point distant from these territories, and followed to observe interactions with Vm fish. The frequency of attacks received by the displaced Not fish was greater than attacks received by Nm residents, indicating that Nm residents had easier access to Vat territories than non-residents did. A possible mechanism for this is reduced aggression of Vm towards Nm residents, as a result of the 'dear enemy' effect that has been reported in territorial contests between rivals. An alternative mechanism is that tolerance towards Nm differs among Vm fish and Nm residents selectively visit more tolerant Vat fish due to previous experience while non-residents randomly approach both tolerant and hostile Vat fish. The ability of Vat to discriminate between Nm residents and non-residents is essential to the former mechanism but not to the latter. To more specifically examine which mechanism works in the Vm Nm commensal system, we will need to follow individually identified Vat fish interacting with Nm residents and non-residents.