Sibling cannibalism among juvenile vundu under controlled conditions. II. Effect of body weight and environmental variables on the periodicity and intensity of type II cannibalism

Cannibalism among starved groups of juvenile (19-48 days old) vundu catfish Heterobranchus longifilis was 66.5% nocturnal, and its impact under modifi ed day length was proportional to the duration of the dark phase. Shallow d epth and high population density decreased the intensity of cannibalism, wh ereas low density and deeper environments had an opposite effect. The prese nce of refuges had no significant effect on cannibalism. The maintenance (R -maint) and maximum (R-max) daily food rations (% day(-1)) of cannibals fee ding 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 i mpact of a cannibal on a population decreased by a 20% margin each time the cannibal doubled its body weight, and suggested that cannibalism among vun du would become insignificant for cannibals heavier than 30 g. The signific ance of these findings is discussed within the contexts of vundu aquacultur e and of general, conceptual models of the dynamics of cannibalism among fi shes. (C) 1999 The Fisheries Society of the British Isles.