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Cannibalism among starved groups of juvenile (19-48 days old) vundu catfish Heterobranchus longifilis was 66·5% nocturnal, and its impact under modified day length was proportional to the duration of the dark phase. Shallow depth and high population density decreased the intensity of cannibalism, whereas low density and deeper environments had an opposite effect. The presence of refuges had no significant effect on cannibalism. The maintenance (R maint ) and maximum (R max ) daily food rations (% day 1 ) of cannibals feeding on live prey were modelled as R maint =3·899 W C 0·327 (r 2 =0·684; d.f.=31), and R max =49.545 W C 0·321 (r 2 =0·999; d.f.=5), where W C was the body weight of the cannibal (g). The latter model indicated that the impact of a cannibal on a population decreased by a 20% margin each time the cannibal doubled its body weight, and suggested that cannibalism among vundu would become insignificant for cannibals heavier than 30 g. The significance of these findings is discussed within the contexts of vundu aquaculture and of general, conceptual models of the dynamics of cannibalism among fishes. 1999 The Fisheries Society of the British Isles

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