Scientists and aquarists alike have long questioned the taxonomic status of the cichlid until recently classified as Melanochromis labrosus.
Was it a Melanochromis? Some morphological details said yes, but colour pattern said no, as it lacks the longitudinal banding that currently forms part of the definition of the genus. Was it even an mbuna, or should it be regarded as a “hap”? No other mbuna has hypertrophied (over-developed and “rubbery”) lips, no other mbuna is such a dull colour.
These questions have now been answered, at least in part, in a new paper by ichthyologists Michael Oliver and Matthew Arnegard. They re-examined the species and confirmed that it does not belong in Melanochromis or any other cichlid genus. Hence they have erected a new genus, Abactochromis, containing just this one species, now Abactochromis labrosus. The name of the new genus is derived from the Latin abactus meaning “banished” and relates to the solitary, non-territorial behaviour of A. labrosus and to its removal from Melanochromis, where it had been incorrectly classified for 75 years!
The scientists also compared their new genus with the characteristics generally used to define the mbuna, and found that it seems to be closer to that group than to the “haps”, although its inclusion in the mbuna is still in question. Because of this doubt and a number of features unique among the mbuna (including the lips), they regard A. labrosus as being extremely important for future genetic research into the relationships between Malawi cichlids in general.
The question of whether or not the A. labrosus is an mbuna caused the authors to also review the physical characteristics and other (DNA) evidence that currently define the mbuna as a distinct group, and to draw up a detailed key to the now 13 genera.
Here too, there are a number of questions that remain unanswered, but indications are that the mbuna belong to a distinct clade (= lineage, branch in the family tree) among Malawi cichlids; however, DNA study suggests that some cichlids not generally regarded as mbuna (including some Aulonocara species) may also belong to this clade. Much further research is required before these and other questions about the evolutionary history and relationships of Malawi cichlids can be resolved.
The paper also looks at what is known of the distribution and ecology of this unusual and interesting cichlid, which, unfortunately, isn’t often seen in the hobby because of its lack of bright colours.
For further information see: Oliver, M. K. & M. E. Arnegard, 2010, A new genus for Melanochromis labrosus, a problematic Lake Malawi cichlid with hypertrophied lips (Teleostei: Cichlidae). Ichthyological Exploration of Freshwaters, 21 (3): 209-232.