The breeding behaviour and distribution of tucunaré Cichla aff. monoculus were studied for 2 months during the breeding season in the Paraguá River, Bolivia. Tucunaré were more abundant in the old remnant channels and isolated lakes than in the main river channel. The breeding period was delayed for c. 1 month in the river compared to the old remnant channels and lakes. The batch fecundity ranged between 3712 and 10 355 for females weighing 460 and 1380 g, respectively. Gonad analysis of egg-guarding or juvenile-guarding females showed that a female was able to spawn more than once during the breeding season. Nests were significantly larger and deeper in the isolated lakes than in the old remnant channels and in the main river. The maximum depth of the nests also differed significantly, being deeper in the isolated lakes than in the river channel and in the old remnant channels. © 2006 The Authors.