The impacts of grazing by tilapias (Oreochromis niloticus L.) on periphyton communities growing on artificial substrate in cages

This study describes the development of periphytic communities established on artificial substrates in tilapia (Oreochromis niloticus) cages during a 10-week experiment conducted in the Meghna River, Bangladesh. Qualitative a nd quantitative characteristics of the periphyton were recorded, including diatom community composition and primary productivity. Fish grazed actively on the periphyton and there was a rapid fall in periphyton biomass followi ng their introduction to the cages. Grazing significantly(P < 0.05) affecte d the horizontal and Vertical periphyton biomass distribution over time. Ti lapia showed only limited feeding selectivity, both animal and plant materi al being removed to an equal extent, although there was less ingestion of s maller particles. Fish grazing significantly (P<0.05) reduced diatom divers ity, mean diatom biovolume, the variability in standing periphyton biomass and the proportion of ash. Grazed periphyton communities were younger, heal thier and more productive. The significance of these findings for caged pro duction of fish are discussed. (C) 2000 Elsevier Science B.V. All rights re served.