Fish communities in central Amazonian white- and blackwater floodplains

In Amazonian floodplains, the flood cycle of the river is becoming the domi nant seasonal factor, and fish communities are found to fluctuate greatly o ver the year. During inundation, fish migrate into floodplain forests to fe ed on fruits and seeds, in an area more than 300 000 km(2) in size. To docu ment patterns of species diversity, distribution, abundance and temporal dy namics and in order to describe the ecological importance of the inundated forest, floodplain fish were captured using variously sized gill nets in wh ite and black water areas inside and outside the floodplain forests during low, rising, high and falling water level in 1990 and 1991. Dominance varie s to some extent in white water between floodplain forest (0.06) and open w ater (0.11) while it is unchanged in black water (0.04). Black water fish c ommunities were more diverse. Most abundant among white water fish were Lip osarcus pardalis, Pygocentrus nattereri, and Pellona flavipinnis, for examp le, or Plagioscion squamsissimus, Serrasalmus rhombeus, and Serrasalmus man ueli in black water. Among the most abundant white water fish, Colossoma ma cropomum, Mylossoma duriventre and Osteoglossum bicirrhosum occurred almost exclusively in inundated forests. Of the black water species there were a large number of species which were captured only in inundated forest, such as Geophagus cf. altifrons, Hoplias malabaricus, Osteoglossum bicirrhosum a nd Uaru amphiacanthoides. Catches varied with sample site, water level and direction of water level change. The average CPUE in white and black water was 190 and 41 g fish m(-)2 and day, respectively, with maximum yields at l ow water and minimum yields at high water. Comparing rising and falling wat er levels, a significantly higher quantity of fishes was captured at fallin g water level. In black water, fish catches from the floodplain forest exce eded the open water catch by 183 to 550%, depending on season. Differences in respect of white water are smaller (106-281%). Fish communities in the a rea under investigation seem to be stochastically assembled, with significa nt differences between white and black water only. Many fishes move into th e floodplain forest not only to feed but probably also for other reasons - to seek shelter, for example.