Journal of Fish Biology (2016) doi:10.1111/jfb.12896, available online at wileyonlinelibrary.com Environmental disturbances and fshes in the Amazon A. L. Val*†, P. M. Fearnside‡ and V. M. F. Almeida-Val* *Laboratory of Ecophysiology and Molecular Evolution, Brazilian National Institute for Research of the Amazon, Manaus, AM, Brazil and ‡Laboratory of Agroecosystems, Brazilian National Institute for Research of the Amazon, Manaus, AM, Brazil Key words: Amazon; environmental conservation; environmental disturbance; fsh; hydroelectric dams. The Amazon is a multi-faceted biome extending across all of the countries in north- ern South America. Aquatic habitats include watercourses of all sizes, beaches, lakes, fooded forests and foodplain areas. White, black and clear water types differ in the amount and nature of their sediments and in their levels of dissolved organic carbon, ion content, pH, water density and temperature. This environmental diversity is added to the regular cycle of changes driven by region’s annual food pulses. Over millions of years, the region has experienced challenges requiring continuous biological adjust- ments of all organisms. These natural constraints are claimed to be the cause of the unparalleled diversity of fsh species in the region. The fshes have developed myriad adjustments at all biological levels to face the never-ending environmental challenges that naturally occur in their habitats (Almeida-Val et al., 1999). These challenges are now joined by recent human distur- bances that are pushing fshes to their biological limits. The scientifc community must therefore focus efforts on developing reliable strategies for biological conservation, and local, regional, national and transnational authorities must promptly adopt these strategies. River damming is one of the most controversial environmental challenges. Hydro- electric dams have both costs and benefts, but the costs (both monetary and non-monetary) are consistently understated and the benefts exaggerated (Fearn- side, 2014). Blocking fsh migration is a critical effect of dams. Many Amazonian fshes have an annual piracema, or mass stock migration ascending Amazon tributaries to breed in the headwaters. The most dramatic case is the blockage of migration of the ‘giant catfsh’ of the Madeira River [including Brachyplatystoma rousseauxii (Castle- nau 1855) and Brachyplatystoma vaillantii (Valenciennes 1840)]. These magnifcent fshes were a major economic and nutritional resource for riverside populations in Brazil, Peru and Bolivia. The large catfshes did not succeed in locating and entering the fsh passages installed at the two dams (Fearnside, 2014). Blocking fsh migration also causes fragmentation of populations and loss of gene fow, which also affects fsh yields. †Author to whom correspondence should be addressed. Tel.: +55 92 36833189; email: dalval@inpa.gov.br 1 © 2016 The Fisheries Society of the British Isles