COMPARATIVE ECOLOGY OF CATFISHES OF THE UPPER ZAMBEZI RIVER FLOODPLAIN

An 8-month survey of the Upper Zambezi River, its associated floodplai n and marginal upland habitats yielded 16 catfish (Siluriformes) speci es; among which Schilbe intermedius comprised over half of the 3534 sp ecimens. Generally catfishes were most abundant in floodplain and rive r channel habitats, but three species (Clariallabes platyprosopos, Syn odontis macrostoma, S. nigromaculatus) were most abundant in the river channel, and three species (Amphilius uranoscopus, Chiloglanis neuman ni, Leptoglanis rotundiceps) were most abundant or restricted within s mall tributary streams. Diet analysis revealed low pairwise dietary ov erlaps, but there was no statistically significant pattern of communit y-wide niche segregation based on prey type. The 16 catfishes fell int o four size/trophic guilds: large carnivores (Clarias gariepinus, C. n gamensis), medium-sized carnivores (C. stappersii, C. theodorae, Paruc henoglanis ngamensis, Clariallabes platyprosopos, Schilbe intermedius) , medium-sized omnivores (Synodontis leopardinus, S. nigromaculatus, S . woosnami, S. sp. cf. woosnami), and small omnivores (S. macrostigma. S. macrostoma, Amphilius uranoscopus, Chiloglanis newnanni, Leptoglan is rotundiceps). No evidence of reproductive activity was detected in any of the catfishes during the survey period of falling and low water conditions. Although catfishes are not as highly valued for food as c ichlid fishes, three species are significant components of local comme rcial and subsistence fisheries: the two large Clarias by virtue of th eir size, and Schilbe by virtue of its great abundance. Abundances of the heavily exploited Clarias gariepinus and C. ngamensis stocks appea r to be lower in the Upper Zambezi compared with the Okavango floodpla in system. (C) 1996 The Fisheries Society of the British Isles