In this review, the development of species concepts is discussed, both in practice and in principle, applied to the cichlid fishes of Lake Malawi. From 1864 to 1935, museum-based taxonomists with no information on the natural biology of the fishes had no alternative but to apply morphological species definitions. Since then, most descriptions have been carried out by field workers, generally employed on applied fisheries projects, again mostly using morphological criteria. The work of Fryer exemplifies the uncertainty over species concepts during this period, simultaneously demonstrating a profound knowledge of evolutionary theory and biological species concepts, and the difficulties of applying them in practice.
Following the pioneering SCUBA-assisted study of Holzberg in 1978, Ribbink and his
co-workers developed a practical species definition for the rocky shore mbuna, based on
male breeding colours in addition to behavioural, ecological and morphological features.
Such practical species definitions are now used by almost all Malawi cichlid researchers,
as well as those working on Lakes Victoria and Tanganyika. Many current workers, including
the present author, believe that the most appropriate theoretical basis for this practice
lies in the proposition that reproductive isolation between species is often the result of
sexual selection by female choice. Rather surprisingly, one implication of this view is that
appropriately designed laboratory studies can be used to test the specific status of
allopatric populations. In a highly speculative discussion, it is suggested here that
speciation mechanisms and species concepts appropriate for African lake cichlids probably
have little relevance for other lacustrine endemic taxa.