Small dams for aquaculture negatively impact fish diversity in Amazonian streams

Abstract

Much has been written about the negative impacts of large hydroelectric dams on fish species diversity in the Amazon River Basin; however, less is known about the impacts of small dams in streams that are created for fish aquaculture. Our study of fish assemblages upstream and downstream of fish farm dams in Rondônia State, Brazil, revealed that the dams act as physical barriers to fish movement and that upstream assemblages showed lower measures of diversity and abundance compared to downstream. The greatest impact was the obstruction of upstream movement of a number of fish groups, coupled with isolation and disappearance of relatively rare fish species living upstream. The fish species most affected were from frugivore, herbivore and detritivore trophic levels that are associated with migration and the forming of schools (potamodromous species), although the impact was also evident in piscivorous fish commonly found in lentic habitats. Although stream dams may cause small negative effects relative to huge hydroelectric barriers, the cumulative impact of hundreds of fish farms in stream channels could be considerable. Amelioration of the damage caused by fish farm impoundments will require (1) design of effective fish passage systems around dams to reduce impact on fish diversity and (2) prohibition of the complete stream blocking to build these fish farms, which will require derivative channels to their water supply.