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Intermediate hosts of Schistosoma haematobium, the causative agent of urinary schistosomiasis, in Lake Malaŵ i include: Bulinus globosus, a member of the B. africanus group and B. nyassanus, a diploid member of the B. truncatus/tropicus species complex. We compared genetic variability between isolates of S. haematobium from the southern part of the lake (Cape Maclear), where both B. globosus and B. nyassanus play a role as intermediate hosts, and isolates from the northern part, where only B. globosus is host. Data show that the S. haematobium isolates from these two areas of Lake Malaŵ i cannot be distinguished using nuclear or mitochondrial sequences and are capable of cross-infections.

We have observed a dramatic decrease in the abundance of snail‐eating fishes and an increase in the prevalence of schistosomiasis among village residents and expatriate tourists at Lake Malawi, Africa, over the past two decades. We hypothesized that these observations were linked by a cause‐and‐effect relationship and that the observed decrease in fish molluscivores permitted an increase in the abundance of snails that are intermediate hosts to schistosomes; we proposed a sampling protocol to determine these relationships. Initially, we thought that intensive study of the interactions among fish, intermediate‐host snails, and human schistosomes in southern Lake Malawi could be applied to other areas throughout the lake. More than two‐thirds of the cichlid species in Lake Malawi are undescribed, the taxonomy of the Bulinus snails is poorly known, and not all strains of Schistosoma hematobium have been identified. Before we can identify the interactions among these components of the system and effectively manage snail‐eating fishes, we must be able to accurately delimit the taxonomic units (e.g., species, populations, and demes) within each of the above groups.

Lake Malaŵi is known for its endemic haplochromine species flock, most notably the rock-dwelling cichlids known as mbuna. One of the larger genera of mbuna is Metriaclima, a group consisting of 31 described species (including the five described herein) and approximately 45 recognized unique populations. Metriaclima is diagnosed by its feeding behavior and several morphological characteristics including the angle of the vomer and the presence of bicuspid teeth in the outer row of both the upper and lower jaws. Metriaclima zebra, the type species for the genus, was described based on a single specimen. While the collection location of this holotype is not known, based on the travel records of its collector, it is likely that the specimen originated from Likoma Island. The holotype was therefore compared to specimens from several localities around this island and was found to be morphologically indistinguishable from some of these. This study includes the morphological analysis of 496 specimens of Metriaclima belonging to 31 collections from Lake Malaŵi. Morphometric differences were analyzed and the relationships among several distinguishable populations of Metriaclima zebra were investigated. Our study further resulted in the description of the following five new species belonging to the M. zebra species com-plex: M. pambazuko, M. lundoense, M. midomo, M. tarakiki, and M. nigrodorsalis. These species were distinguished and described based on color patterns, morphometric, meristic, and ecological differences. These new species were compared with and distinguished from nearby populations of Metriaclima having similar pigmentation patterns and/or similar eco-logical niches. An artificial dichotomous key to the described species of Metriaclima is presented.

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