Comparative ecology of catfishes of the Upper Zambezi River floodplain
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An 8-month survey of the Upper Zambezi River, its associated floodplain and marginal upland habitats yielded 16 catfish (Siluriformes) species, among which Schilbe intermedius comprised over half of the 3534 specimens. Generally catfishes were most abundant in floodplain and river channel habitats, but three species (Clariallabes platyprosopos, Synodontis macrostoma, S. nigromaculatus) were most abundant in the river channel, and three species (Amphilius uranoscopus, Chiloglanis neumanni, Leptoglanis rotundiceps) were most abundant or restricted within small tributary streams. Diet analysis revealed low pairwise dietary overlaps, but there was so statistically significant pattern of community-wide niche segregation based on prey type. The 16 catfishes fell into four size/trophic guilds: large carnivores (Clarias gariepinus, C. ngamensis), medium-sized carnivores (C. stappersii, C. theodarae, Parauchenoglanis ngamensis, Clariallabes platyprosopos, S. nigromaculatus, S. woosnami, S. sp. ef. woosnami), and small omnivores (S. macrostigma, S. macrostoma, Amphilius uranoscopus, Chiloglanis neumanni, Leptoglanis rotundiceps). No evidence of reproductive activity was detected in any of the catfishes during the survey period of failing and low water conditions. Although catfishes are not as highly valued for food as cichlid fishes, three species are significant components of local commercial and subsistence fisheries: the two large Clarias by virtue of their size, and Schilbe by virtue of its great abundance. Abundances of the heavily exploited Clarias gariepinus and C. ngamensis stocks appear to be lower in the Upper Zambezi compared with the Okavango floodplain system.