Downstream passage through fish ladders and other facilities remains largely uninvestigated in South America. In view of this concern, we monitored ascending and descending fish movements through the fish ladder at Peixe Angical Dam, upper Tocantins River, Brazil, between September 2009 and August 2010. To investigate the extent of downstream passage, the fish fauna was sampled monthly (i) at sites upstream and downstream from the dam and (ii) inside the ladder. To distinguish between ascending and descending movements, the fish ladder remained open (permanent water flow), but a screen blocked the complete passage of fish in both directions. The results of the study indicated that the ladder restricts fish movements in both directions. Few species were found to use the ladder (31 out of 119 species recorded in the area). Moreover, monitoring revealed that downstream passage is even more limited. Only 18 species were recorded moving downstream. In addition, few fish attempted to move downstream during the year; of all fish captured in the ladder (n = 17,335), only 4% were descending. Species performing exclusive downstream movements were numerically rare or infrequent. Most downstream captures involved only four species. We emphasize that several species performed one-way upstream movements or showed a high density of ascending fish. Consequently, the numerical ratio between ascending and descending fish (ind./m 2 ) showed high positive values throughout the year (644:1 on average, considering all species); migratory species showed higher ratios (1069:1). The results of the study show that the facility fails to support the downstream passage of migratory and non-migratory fishes. We conclude that the fish ladder at Peixe Angical Dam does not play a conservation role and may complicate alternative conservation efforts.A passagem descendente de peixes em mecanismos de transposição permanece pouco investigada na América do Sul. Inspirado nessa falha, o presente estudo monitorou a escada de peixes instalada na barragem da UHE Peixe Angical, alto rio Tocantins, entre setembro de 2009 e agosto de 2010. Para investigar a extensão da passagem rio abaixo, a fauna de peixes foi amostrada mensalmente em (i) locais acima e abaixo da barragem, e (ii) dentro da escada. Para identificar corretamente movimentos ascendentes e descendentes dentro da escada, o mecanismo permaneceu aberto (fluxo permanente de água), mas uma tela impediu a passagem completa dos peixes em ambas as direções. Os resultados indicam que a escada é restritiva ao movimento dos peixes em ambos os sentidos, considerando que poucas espécies tiveram acesso ao mecanismo (de um total de 119 espécies na área, apenas 31 ocorreram na escada). O monitoramento revelou, entretanto, que a passagem descendente é consideravelmente mais limitada; apenas 18 espécies foram registradas descendo o mecanismo. Além disso, poucos peixes tentaram descer a escada ao longo do ano; de todos os peixes capturados na escada (n = 17,335), apenas 4% desempenhava movimentos descendentes. ...