Management of interspecific food competition in fish-crayfish communal culture: the effects of the spatial and temporal separation of feed

Interspecific competition for food in polyculture is enhanced in intensive systems because the cultured species mostly depend on artificial feed. This study evaluated the effectiveness of spatially and temporally separating t he feed for red hybrid tilapia and redclaw crayfish (Cherax quadricarinatir s) as a means of decreasing interspecific competition and increasing the pe rformance of each species in communal culture. The effects of the spatial a nd temporal separation of feed (i.e., feeding with sinking and floating pel lets vs. sinking pellets only, and by day and night vs. day only, respectiv ely) were tested in a 2 x 2 factorial design. Two 6-week experiments were c onducted involving inverse fish-crayfish size relationships. Monocultures o f each species were included as controls. No effects of the spatial and tem poral separation of feed on the survival and growth of tilapia were found. However, tilapia grew better in duoculture than in monoculture. The perform ance of redclaw was generally better in monoculture than in duoculture with tilapia. The magnitude of the deleterious effect of tilapia on redclaw was size-dependent, as reflected in reduced survival, growth and foraging of s mall redclaw in the presence of relatively larger tilapia. There was a sign ificant effect of the temporal separation of feed on the growth of small cr ayfish; feeding them at night increased their growth by 32%. The temporal s eparation of feed, in which redclaw were fed at night and tilapia during th e day, proved to be an appropriate feeding strategy in their communal cultu re. (C) 2001 Elsevier Science B.V. All rights reserved.