SynopsisWe compared ecological and morphological patterns among cichlid faunas from three different biotic regions : the Rfo Tortuguero/Rio Sarapiquf in Costa Rica, the Rfo Apure drainage in Venezuela, and the Upper Zambezi drainage in Zambia . Cichlids comprise 19 percent of the fish fauna in the Tortuguero and Upper Zambezi drainages and 6 .5 percent in the Apure drainage. Cichlid faunas exhibited similar patterns of habitat and food resource utilization, although vegetation-dwelling is more common and detritivory and herbivory are rarer in the Apure fauna . We hypothesize that South American ostariophysan fishes were more preadapted than cichlids to exploit detritivore and herbivore niches . The Zambezi cichlid fauna shows less ecomorphological diversification than the other two faunas, even though the degree of dietary diversification is similar among faunas . Chaetobranchus flavescens from the Venezuelan fauna is the only species that specializes on zooplankton as an adult, and algae grazing (Neetroplus nematopus) and specialized fruit feeding ('Cichlasoma' tuba) were represented only in the Costa Rican fauna. Based on the most recent hypothesized phylogeny for the family Cichlidae, we identified numerous interfaunal ecomorphological and feeding niche convergences . Patterns of ecomorphological divergence in relation to cladogenesis indicate a faster rate of evolutionary niche diversification in Central American cichlids compared with the two other faunas .

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The ecology of sympatric African pike, Hepsetus odoe (Hepsetidae), and tiger fish, Hydrocynus forskahlii (Characidae), were compared during high (May‐August) and falling water (September‐December) conditions in the Upper Zambezi R. drainage of Zambia. Both species were common in the central and southern regions of the river and associated floodplain, and Hydrocynus was common in the northern region in swift flowing tributaries where Hepsetus was rare. Hepsetus inhabited vegetated environments of river backwaters, lagoons, and sluggish tributaries, whereas Hydrocynus occupied the open water of the main river channel almost exclusively. During the period of annual flooding, juveniles of both species coexist in flooded savanna regions. Size distributions of adult Hydrocynus and Hepsetus changed relatively little between high and low water conditions. Stomach contents analysis indicated that adult size classes of both species are almost entirely piscivorous, and both show diet shifts with changes in size. Only very small seasonal diet shifts were noted. Approximately 50% of the diet of Hepsetus consisted of haplochromine cichlid fishes, but also included large numbers of tilapine cichlids and mormyrids, Hydrocynus consumed primarily cichlid fishes, but also consumed large percentages of Hepsetus and small characid fishes. Small size classes of Hepsetus fed heavily on small machokid catfishes (Synadontis spp.) and later shifted to a diet of cichlids and mormyrids, and small Hydrocynus preyed heavily on Barbus spp. (Cyprinidae), small characids, and mormyrids. Ratios of prey length‐predator length averaged approximately 0·26 for Hydrocynus and nearly 0·40 for Hepsetus. The large potential for food resource competition appears not to be realized due to a very high degree of habitat partitioning between larger size classes of the two species. At the interface between river backwaters and channel habitats, Hydrocynus is a significant predator of Hepsetus, a factor that should further restrict the occurrence of the latter in open areas of the main channel.

Habitat use and diets of five tilapiine populations of the Upper Zambezi River Basin in Zambia, south‐central Africa, were examined during the 8 month descending phase of the annual hydrological cycle. All species occurred across a range of habitats, with most individuals captured from lagoons. Tilapia rendalli, a macrophyte feeder, was the only dietary specialist. Ontogenetic diet shifts were not observed over the size range examined (30–320 mm LS). Algae were uncommon in tilapiine diets. Tilapia ruweti, the smallest tilapiine in the region, was the only species that consumed more algae (filamentous algae) than detritus. Oreochromis andersonii, Oreochromis macrochir and Tilapia sparrmanii had high dietary overlap and occurred in the same habitats in similar relative abundances. High overlap in habitat use and diet among tilapiines contrasted with findings from a comparable analysis of predatory haplochromine cichlids of the region that revealed strong ecological segregation and niche complementarity during the annual descending‐water phase.

A new cichlid species, Serranochromis altus, from the Upper Zambezi River is described. It is sympatric with its deep-bodied sister species, S. angusticeps, within the Upper Zambezi and Kafue River drainages. Both immatures and adults of the new species can be distinguished from S. angusticeps on the basis of morphometric characters and color pattern, including the absence of distinct speckles on the face and chest and eye stripes that are diagnostic of the latter. Serranochromis altus has a shorter snout, larger eyes, wider head features, and longer pectoral fins than S. angusticeps of similar size. Both sexes of the new species mature at a larger size and appear to attain larger maximum sizes than S. angusticeps. During the low water period, S. altus inhabits deep regions of the main Zambezi River channel and feeds primarily on nocturnal mormyrid and schilbeid fishes. In contrast, S. angusticeps dwells in densely vegetated regions of quiet backwaters and lagoons of the Barotse floodplain where it ambushes small characids and cyprinids.