Carbon sources of Amazonian fisheries

Variation in the seasonal and spatial isotopic composition of plant C-4 (aq uatic macrophytes) and C-3 (forest, C-3 aquatic macrophytes and algae), and that of fish [Prochilodus nigricans Agassiz, Mylossoma duriventre (Cuvier) , Colossoma macropomum (Cuvier), Semaprochilodus insignis (Schomburgk) and S. taeniurus Steindachner] in the Amazon floodplain were analysed to test w hether the fisheries deliver plant carbon to the population of Manaus in th e same proportion as it is available in the floodplain. The contribution of C-4 plants was significantly lower in C-13 during the season of high water levels and increased toward the west of the basin. Mylossoma duriventre an d C. macropomum changed delta(13)C levels, while the delta(13)C of P. nigri cans and C. macropomum shifted spatially. The contribution of C-4 to the fi sheries yield was small. C-3 plants (excluding phytoplankton) also contribu ted less than expected. This was explained by the importance of detritivore s to the yield of the fisheries and the dependence of these species on alga l carbon.