The standing crop and distribution of fish within the floating meadow habitat of Lago Mamirauá, an upper Amazonian floodplain lake, were studied during December 1993 when the water was rising and had just begun to enter the forest. The ichthyofauna was dominated by six groups, the Anostomidae, Gymnotiformes, Erythrinidae, Serrasalmidae, Synbranchidae and Cichlidae. For anchored meadow, total wet weight was estimated as 312 kg ha ‐1 and total number as 90 400 individuals ha‐1. This biomass estimate was probably below the annual maximum because some fish had already dispersed into the forest, but, the number of individuals was close to the annual maximum because of the recent arrival of juvenile Serrasalmidae and Cichlidae. For drifting islands of meadow fish biomass and density were estimated as 192kg ha‐1 and 12 700 individuals ha‐1 respectively. The Synbranchidae, Gymnotiformes and Erythrinidae avoided drifting meadow. In comparison, the Cichlidae and Anostomidae, while favouring marginal, anchored meadow, were frequently dispersed by drifting islands. The Siluriformes were unique in favouring drifting over anchored meadow. For this group the observed down‐stream drift may be a seasonal migration to the main river channels. Juvenile fish avoided drifting islands, presumably to avoid being flushed from the lakes. Their abundance was lowest at the mouth of the lake. The generally abundant Serrasalmus spp. juveniles were absent from meadow at the mouth of the lake.

Freshwater mussels are often relocated from existing beds for both conservation and management reasons. In this study, we empirically tested whether the habitat type at the destination site was important in predicting the success of mussel relocation. In 1993, four species of freshwater mussels were relocated in the Apalachicola River in Florida, into three distinct habitat types: stable sand, limestone/sand and cobble. The conditional probability of survival of relocated mussels varied by species and habitat. Two species were considered habitat specialists, one species was considered a habitat generalist and recovery rates for the fourth species were too low to assess habitat preferences. We show empirically that microhabitat is important in the survival of relocated mussels and that the habitat‐specific criteria for relocation is species specific. These results suggest that survival of relocated mussels can be enhanced if species‐specific site selection criteria are developed using quantitative information. © 1997 John Wiley & Sons, Ltd.