A four-year survey of the prawn #Macrobrachium amazonicum$ (Heller, 1862) on the Tocantins river studies the short-term impact of the Tucurui hydroelectric project on downstream fishery and reservoir populations. The furthest downstream site below the dam has been the most affected. Before the closure of the dam, the annual prawn catch in Cameta and the flood intensity were directly linked by a linear relation. The prawn production decreased after the closure of the dam from 121 t in 1985 to 60 t in 1986, increased up to 91 t in 1987, but decreased to 62 t in 1988. But the introduction of post-dam data in the linear flood/catch model did not modify the regression slope. The catch variation is partly explained by a stock decrease, and partly by a change in fishing effort. However the seasonal pattern of prawn captures, population size and reproduction intensity have not been affected. Sampling conducted further upriver showed no significant difference in relative abundance, mean size and reproduction characteristics throughout the study period. (D'après résumé d'auteur
