1. Previous comparative analyses of fish communities in European lakes have mainly focused on the response of community composition to eutrophication. In addition, frequently only one or two lake habitats have been sampled. 2. Here, we present fish community data from 67 lakes in north-east Germany. Fish abundance was estimated in littoral, benthic and pelagic habitats from which a composite parameter indicating lake-wide relative species abundances was derived. This parameter was used in group comparisons and non-metric ordination procedures to explore, among 40 lake habitat descriptors sampled, those most important in structuring community composition. 3. Fish community composition was mainly determined by maximum and mean depth, chlorophyll a content and lake volume. The impact of anthropogenic alterations of shore structure and human-use intensity of lakes were of minor importance. The dominant fish species were vendace Coregonus albula, perch Perca fluviatilis, smelt Osmerus eperlanus and several cyprinids (roach Rutilus rutilus, bream Abramis brama, white bream Abramis bjoerkna and bleak Alburnus alburnus). 4. A response of relative species abundance to lake productivity could be demonstrated for small perch, ruffe and bream. However, when the relationship between lake morphology and productivity was controlled for, differences in species abundances were not longer attributable to differences in productivity, but to maximum lake depth. 5. This suggests that there are two distinct fish community types in Germany, namely the cold-water community with vendace and perch inhabiting deeper lakes, and the warmwater cyprinid community inhabiting more shallow lakes. The previously established conceptual model of a community succession from salmonids through perch to cyprinids with increasing eutrophication is hence not continous, but includes a switch between two lake and fish community types.

Fresh data on the timing and speed of the oceanic spawning migration of European eels suggest a new paradigm for spawning ecology.

Summary 1.With the implementation of the European Water Framework Directive, the need for studies on European lake fish communities has increased to include lake type-specific fish community features. Although several standardized fish sampling methodologies are available, most previous fish community studies lack a simultaneous consideration of the littoral, benthic and pelagic habitats of lakes. 2.To compare habitat-specific fish communities, we sampled 67 lakes in the northeastern German lowlands using Norden multimesh gillnets in the benthic and pelagic habitats, and electrofishing in the littoral zone. 3. Standardized catches and diversity of the fish community differed among the three habitats sampled. Species richness and Shannon diversity were higher in benthic and littoral habitats compared with pelagic habitats. Overall, the benthic habitat had the most homogeneous catches and contained the most diverse fish community. 4. Cluster analysis and subsequent indicator value analyses produced substantially different optimum cluster numbers for the three habitat-specific fish communities. Based on the significant differences in fish community composition among the habitats, a simultaneous consideration of numerical fish catches from all habitats was performed using standardized fish abundances. 5. The cluster analysis of the combined abundances resulted in three groups of lakes that were indicated by three fish species. Morphological descriptors (volume, area, maximum depth, mean depth) and descriptors related to the trophic situation (conductivity, total phosphorus) clearly distinguished the three lake groups. 6. All three habitats showed distinct characteristics with respect to either species diversity or relative species' abundances. Our results do not support a conceptual model for all lakes of a gradual succession of fish communities as a result of eutrophication. 7. Synthesis and applications. Only simultaneous consideration of all lake habitats will fulfil the requirements of the Water Framework Directive for evaluating the ecological integrity of lakes. A pre-separation into at least two community types according to lake morphology is necessary before the deviation of the present fish community relative to a reference state can be determined.

Recruitment of European eels (Anguilla anguilla) has declined to the extent that they have been added to the IUCN Red List of Threatened Species. Therefore, it is critical to ensure that eels complete their outward river migration in order to contribute to the available spawning stock. We conducted a 4-year (2007)(2008)(2009)(2010)(2011) telemetry study to understand the migratory behaviour and potential impact of environmental factors on the eel during this critical life stage.Out of 399 female eels tagged with acoustic transmitters, only 28% demonstrated clear downstream migratory behaviour. Fifty-five percent were detected exhibiting no downstream migration behaviour and 17% were not detected at any monitoring station. Movement patterns of downstream-migrating (silver) eels were characterized by nocturnal activity and seasonal migration, with distinct peaks in autumn and spring. Migration was often discontinuous and exhibited phases of active locomotion and expanded stopovers. The most important determinants of movement activity were water temperature, cumulative precipitation and moonlight, although the significance varied by season and location in the river basin.Our results evidence a discontinuous, stepwise migration over an extended period. Furthermore, our findings indicate that migration success depends on holding duration prior to tagging and environmental predictors with varying importance depending on the season, as well as the locations of capture, tagging and release.

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