How are Malawi Cichlids Classified?

ince the earliest scientific descriptions of cichlids from Lake Malawi (see Who Pioneered Malawi Cichlid Taxonomy?), species believed to be related to each other have been classified into the same genus on the basis of intuition, and species seen as isolated or especially distinct have been made the types of new genera.

An early classification of these cichlids was that of C.T. Regan (1922), who divided the 84 species then known from "Lake Nyassa" into 15 genera (Tilapia and 14 haplochromine genera). Soon after, many additional species were discovered by Cuthbert Christy in 1925-26 (Christy was later killed by a Cape buffalo). Ethelwynn Trewavas revised the entire fauna, first treating the genus Lethrinops (Trewavas, 1931) and then, in a brief synopsis, all the other genera (Trewavas, 1935).

Geoffrey Fryer, in conjunction with his pioneering ecological studies (Fryer, 1959a), described several new species in the mbuna flock in 1956 and 1957, and T.D. Iles (1960) revised the utaka group of zooplankton-feeding "haps." Oliver & Loiselle (1972) described the first new mbuna genus since Trewavas's synopsis. Many other persons soon began naming and describing individual species of Malawi cichlids from the '70s to the present. These species descriptions, regrettably, were often published in aquarium magazines by persons not trained in taxonomy, and these often-inadequate descriptions will be very difficult for future taxonomists to find (because these magazines are not deposited in the world's research libraries as scientific journals are).

Several genera in the "hap" flock have been revised during the last quarter-century. In the mbuna flock, the most notable contribution has been the detailed rocky shore survey of Ribbink et al. (1983).

Today, we understand that the best basis for biological classification is cladistic or phylogenetic analysis of the organisms to infer their historical branching pattern of common ancestry. [For more information, you can leave this web site to Journey into the World of Phylogenetic Systematics (Cladistics).] However, cladistics on such a complicated fauna as that of Lake Malawi is daunting — see below. The only attempt at classifying even a large fraction of the Malawi cichlid fauna since Trewavas's synopsis (1935) is the still essentially intuitive classification of Eccles & Trewavas (1989) on the "hap" flock; they did not consider the mbuna flock, by now known to be quite speciose. Eccles & Trewavas added numerous new genera, several of them monotypic (and thus monophyletic!), many others ill-defined and probably not monophyletic.

ventually, Malawi cichlids, and all organisms, may be arranged in a stable cladistic (phylogenetic) classification, perfectly reflecting detailed and well-corroborated hypotheses of the relationships of common ancestry for all of the species. At present, however, we still understand very little of the phylogenetic relationships of these fishes, and so they are still classified more or less intuitively. Much work remains to be done even at the "alpha level" of description of populations and species. By some estimates, only half of all Malawi cichlid species have even been named and described, let alone understood in terms of phylogeny. But there is reason to hope that the phylogeny will be inferrable. A number of distinctive melanic (black) color patterns occur in the "hap" flock, some of which are unique to the cichlids of Malawi, and the latter unique patterns seem to provide information with which to group related species. These characters have not been fully exploited (but see Are There Any Cladistic Analyses of Malawi Cichlids?). A wealth of data from the scales, and their arrangement on the fish, awaits analysis for Malawi cichlids and shows great promise, judging by results on the cichlids of Lakes Victoria, Edward, and Kivu (Lippitsch 1993, 1995).

Analysis of DNA sequences is also an exciting phylogenetic tool, but the results must still be interpreted with caution. The apparently best DNA method for phylogeny reconstruction derived so far makes use of microsatellite flanking regions. Yet, two variants of a method for deriving consensus trees from the data both suggested a quite surprising phylogeny: Among east African cichlids, the Malawi mbuna genus Labidochromis came out as the sister taxon of a group including the riverine, Lakes Victoria-Edward-Kivu, and Lake Tanganyikan genera Serranochromis, Astatotilapia, Astatoreochromis, Pseudocrenilabrus, Tropheus, and Chalinochromis (Zardoya et al., 1996). If this is correct (which I doubt), a lot of morphologically based hypotheses will need to be reworked (not that there's anything wrong with that)!

The Cichlid Fishes of Lake Malawi, Africa: MalawiCichlids.com