The Samuel dam is located 50Km from Porto Velho, Rondônia, on the Jamari river, the first right margintributary of Madeira river, in Brazil. Construction began in April, 1982 and the turbines went on line seven years later. A comparative study of the ichthyofauna was undertaken in the water bodies influenced by the dam, during both pre and pos impoundment phases. The study shows that ichthyofauna was seriously affected by the dam: there was an overall decrease in fish diversity, while a few species increased their numbers, including: Cichlasp. (tucunare), Schizodon fasciatus(aracu comum), Hypophthalmus marginatus(mapará) and Serrasalmus rhombeus(piranha preta). Just below the dam, the population of a small Pimeloclusspecies (mandi) increased. Reduction on dctrilivorous and frugivorous fishes and increase in piscivorous was also observed, The fish communities in the main chanci appear to have been more affected by the dam than the communities of the river marginal lakes. Fishing activity, previously restricted to the Jamari's mouth, now occors intensively in the reservoir, as well, where it constitutesa serious problem for fishery management. These aspects are briefly commented and some options are proposed to guarantee the fish sustainability harvests in the area.", 'en
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