The Amazon basin hosts the Earth's highest diversity of freshwater fish. Fish species have adapted to the basin's size and seasonal dynamics by displaying a broad range of migratory behaviour, but they are under increasing threats; however, no study to date has assessed threats and conservation of Amazonian migratory fishes. Here, the available knowledge on the diversity of migratory behaviour in Amazonian fishes is synthesized, including the geographical scales at which they occur, their drivers and timing, and life stage at which they are performed. Migratory fishes are integral components of Amazonian society. They contribute about 93% (range 77–99%) of the fisheries landings in the basin, amounting to ~US$436 million annually. These valuable fish populations are mainly threatened by growing trends of overexploitation, deforestation, climate change, and hydroelectric dam development. Most Amazonian migratory fish have key ecological roles as apex predators, ecological engineers, or seed‐dispersal species. Reducing their population sizes could induce cascading effects with implications for ecosystem stability and associated services. Conserving Amazonian migratory fishes requires a broad portfolio of research, management, and conservation actions, within an ecosystem‐based management framework at the basin scale. This would require trans‐frontier coordination and recognition of the crucial importance of freshwater ecosystems and their connectivity. Existing areas where fishing is allowed could be coupled with a chain of freshwater protected areas. Management of commercial and subsistence species also needs fisheries activities to be monitored in the Amazonian cities and in the floodplain communities to allow assessments of the status of target species, and the identification of management units or stocks. Ensuring that existing and future fisheries management rules are effective implies the voluntary participation of fishers, which can be achieved by increasing the effectiveness and coverage of adaptive community‐based management schemes.

Questionnaires were used to collect data from the low‐Solimões/high‐Amazon region, Brazil, between December 1992 and February 1994. Gillnets, fishing rods and castnets were the preferred gear used. Gillnets were used throughout the year whilst other gears were used only in certain periods of the year. The fish caught tended to supply family needs but a high proportion were sold in regional markets. Curimatã (Prochilodus nigricans), pacu (various Myleinae) and ruelo (young Colossoma macropomum) were the most frequent species caught. Around 50% of the fish caught in these fisheries was consumed fresh, and the remainder was stored under ice or salted. Fish is the most important source of animal protein for this region, with an annual mean consumption rate of 550 g capita−1 day−1. The fishery has changed from a subsistence to a commercial scale, which was associated with increasing cattle ranching activities. This may have serious social and economic implications.

The fish community of the Solimões floodplain lakes was studied by bimonthly samples taken from May 2001 to April 2002. These were carried out at lakes Maracá (03º51'33"S, 62º35'08,6"W), Samaúma (03º50'42,1"S, 61º39'49,3"W), and Sumaúma and Sacambú (03º17 '11,6"S and 60º04'31,4"W), located between the town of Coari and the confluence of the Solimões and Negro rivers. Collections were done with 15 gillnets of standardized dimensions with several mesh sizes. We collected 1,313 animals distributed in 77 species, belonging to 55 genera of 20 families and 5 orders. Characiformes was the most abundant Order, with a larger number of representatives in the Serrasalmidae and Curimatidae. The most abundant species in the samplings were Psectrogaster rutiloides (132 individuals), Pigocentrus nattereri (115 individuals), and Serrasalmus elongatus (109 individuals). Lakes Samaúma, Sacambú, and Sumaúma were adjusted to logarithmic and lognormal series. The diversity exhibited an inverse gradient to the river flow, showing the highest diversity at Lake Sumaúma, followed by Samaúma, Sacambú, and Maracá. Species richness estimated through the jackknife technique ranged from 78 to 107 species.

RESUMOO uso de bioindicadores pode constituir uma importante ferramenta para monitoramento ambiental, e para ecossistemas aquáticos o uso de espécies de peixes é bastante eficiente, pois são componentes comuns e de fácil amostragem, bem como podem apresentar diferentes estilos de vida e habitats durante seu ciclo de vida. Neste artigo utilizamos como critérios para a seleção das espécies indicadoras, as seguintes características: ser taxonomicamente bem definido e facilmente reconhecível por não-especialistas, apresentar distribuição geográfica ampla, ser abundante ou de fácil coleta, preferencialmente possuir tamanho médio/grande, apresentar baixa mobilidade e longo ciclo de vida, dispor de características ecológicas conhecidas e ter possibilidade de uso em estudos em laboratório. Desta forma, indicamos oito espécies de peixes típicos das várzeas amazônicas: Pellona castelneana, Potamorhina altamazonica, Prochilodus nigricans, Mylossoma duriventre, Pygocentrus nattereri, Serrasalmus rhombeus, Triportheus angulatus e liposarcus pardalis, para uso como bioindicadores em programas de monitoramento ou de avaliação de alterações ambientais. INTRODUÇÃOO termo "bioindicadores" pode ser definido como a escolha de espécies dada sua sensibilidade ou tolerância a diversos tipos de alterações ambientais, geralmente causadas por ações antropogênicas, como poluição orgânica, assoreamento, construção de barragens, pesca predatória entre outros (Washington, 1984, Agostinho et al., 2005. Os indicadores biológicos são muito úteis por sua especificidade em relação a certos tipos de impacto, já que inúmeras espécies são comprovadamente sensíveis a um tipo de poluente e mais tolerantes a outros (Washington, 1984). Assim índices podem ser criados especificamente, conforme o tipo de impacto ambinetal, para se detectar derramamento de óleo, poluição orgânica, alteração de pH e oxigênio na água, lançamento de pesticidas, entre outros fatores (Buss et al., 2003).De forma geral, quanto mais rápido for a identificação de fatores que propiciem condições adversas ao ambiente, maior será as chances de mitigação deste impacto aos níveis superiores da organização biológica como comunidades e ecossistemas (Arias et al., 2007) (Figura 01) Figura 01 -Representação esquemática da organização biológica durante um tipo de impacto negativo no ambiente (adaptado de Arias et al., 2007).