Male mbuna display more aggression towards similarly coloured fish, according to a study published in the most recent issue of the journal Biology Letters.
Michael Pauers, Joshua Kapfer, Christopher Fendos and Craig Berg examined aggression by male red top cobalt zebra (RTCZ; Metriaclima mbenjii) towards conspecific opponents, similarly coloured heterospecific opponents and differently coloured heterospecifics.
The authors videotaped the interactions of focal male RTCZ for 10 minutes in aquarium setups that also had a single male of one of three species: another RTCZ, Labeotropheus fuellerboni (a species having a similar colour pattern as RTCZ), and Metraclimia zebra Chilumba (a congener with a different colour pattern).
They then repeated the experiments, this time with different combinations of two opponents of different species (RTCZ-Metraclimia zebra Chilumba; RTCZ-L. fuelleborni; L. fuelleborni-Metraclima zebra Chilumba).
The researchers found that in trials where focal males were offered a single opponent, the total number of aggressive behaviours did not vary among opponent species, but the types of behaviours did; focal males directed more lateral displays towards conspecifics than towards the other opponent species.
When focal males were offered two opponents simultaneously, the RTCZ males directed significantly more aggressive behaviours and more lateral displays towards similarly coloured opponents, regardless of species.
The authors conclude ur findings suggest a novel role for male nuptial coloration in the mbuna of Lake Malawi: the identification of opponents and the modulation of aggressive behaviour towards them.
Although this has been demonstrated in Lake Victoria cichlids, our results are among the first, to the best of our knowledge, suggesting that aggression among the mbuna is modulated via male coloration.
This implies that male"male aggression plays a role in the distribution of mbuna species throughout Lake Malawi, and explains why similarly coloured congeners are rarely found in sympatry.
For more information, see the paper: Pauers, MJ, JM Kapfer, CE Fendos and CS Berg (2008) Aggressive biases towards similarly coloured males in Lake Malawi cichlid fishes. Biology Letters 4, pp. 156"159.