Lethrinops

Abstract: The 500–1000 cichlid species endemic to Lake Malawi constitute one of the most rapid and extensive radiations of vertebrates known. There is a growing debate over the role natural and sexual selection have played in creating this remarkable assemblage of species. Phylogenetic analysis of the Lake Malawi species flock has been confounded by the lack of appropriate morphological characters and an exceptional rate of speciation, which has allowed ancestral molecular polymorphisms to persist within species. To overcome this problem we used amplified fragment length polymorphism (AFLP) to reconstruct the evolution of species within three genera of Lake Malawi sand-dwelling cichlids that construct elaborate male display platforms, or bowers. Sister taxa with distinct bower morphologies, and that exist in discrete leks separated by only 1–2 m of depth, are divergent in both sexually selected and ecological traits. Our phylogeny suggests that the forces of sexual and ecological selection are intertwined during the speciation of this group and that specific bower characteristics and trophic morphologies have evolved repeatedly. These results suggest that trophic morphology and bower form may be inappropriate characters for delineating taxonomic lineages. Specifically the morphological characters used to describe the genera Lethrinops and Tramitichromis do not define monophyletic clades. Using a combination of behavioural and genetic characters, we were able to identify several cryptic cichlid species on a single beach, which suggests that sand dweller species richness has been severely underestimated.

Abstract: Exploratory trawl data were used to define demersal fish stocks of Lake Malawi in terms of abundance by depth and area. The mean weight of the catch generally declined with increasing depth. A comparison of initial standing stock estimates and the yield from a commercial fishery over a 7 year period suggests a potential yield of less than half of the initial stock. Over 160 species of fish have been identified in the trawl catch of which over 80% by weight were cichlids. Some of the commonest species of cichlids are listed. The composition of the catch in the heavily exploited southern end of the lake has changed from one dominated by large species of Haplochromis sp. and Lethrinops sp. to one dominated by smaller species.

Abstract: Haplochromis micrentodon Regan is transferred to the genus Lethrinops and redescribed. Two new species of Lethrinops which, like the above, are characterised by the possession of lower pharyngeal bones bearing close pavements of slender blunt-tipped teeth are described. 1 Senior Fisheries Research Officer, Fisheries Research Station, P.O. Box 27, Monkey Bay, Malawi. 2 Fisheries Research Officer, Fisheries Research Station, P.O. Box 27, Monkey Bay, Malawi. RHODES UNIVERSITY PRESS