No abstract

Knowledge of the movements and diel behaviour of the European catfish (Silurus glanis), the largest European freshwater fish, is limited to anecdotal information. In a preliminary telemetry study of European catfish, the spring diel movement patterns of five adult catfish were examined. After intraperitoneal insertion of the acoustic tags, the positions of the fish were recorded automatically in the Flix Reservoir (River Ebro, NE Spain). A marked nocturnal mobility pattern was observed throughout the study. During daytime, the catfish were consistently located in the littoral zone and spent extended periods of the day hidden in concealed habitats. Catfish movements were in a radial pattern, with upstream and downstream excursions followed by returns to a previously occupied location. Significant individual variations in movement pattern were observed among the tagged fish and within the 24 h cycle for each fish. Mean instantaneous swimming speed was 0.17 body lengths per second (BLÆs)1) at night but 0.09 BLÆs)1 during the daytimeThis study was financed by the Spanish Ministry of Science and Technology (REN2003-00477

–  The relationship of water quality and fish assemblages has been poorly documented in European reservoirs, despite being important for water management and ecological monitoring. We sampled the fish assemblages of 14 Spanish reservoirs by boat electrofishing in the littoral and multi‐mesh gillnets in the limnetic zone. Simultaneously, we assembled eight physical descriptors and we measured 20 water quality features of the reservoirs. Multivariate analysis (ordination methods and generalised additive models) showed that altitude and trophic state (indicated by chlorophyll or nutrient concentrations) independently explained most of the variation of fish assemblages in these reservoirs. The most eutrophic reservoirs were dominated by common carp (Cyprinus carpio) whereas oligotrophic reservoirs presented other fish species intolerant to pollution rather native (such as brown trout, Salmo trutta). The absolute and relative abundance of common carp was strongly related to the trophic state of the reservoir and 40% of its variation was explained by total phosphorous concentration. Despite clear changes in species composition, there was no significant effect of water quality on overall fish richness or Shannon's diversity, suggesting that for such low richness assemblages species composition is a better indicator of cultural eutrophication of reservoirs than fish diversity.

The European catfish, Silurus glanis, is native to eastern Europe and western Asia and is among the largest freshwater fish in the world. Despite its increasing economic importance and its frequent introductions, the ecology and life-history of this species is poorly known due to the difficulty of sampling such a large species in large rivers and standing waters. Our study provides the first data on age and growth of this species in Turkish waters, where it is native. We report the length-weight relationships and age and size structure of this population, which were significantly different between females and males. A marginal increment analysis indicated that annulus formation occurred between May and June. The estimates of three growth functions (von Bertalanffy, logistic and Gompertz) are reported, with the von Bertalanffy growth providing a better fit and more realistic parameter estimates. Growth rates were significantly higher in males than in females and were overall higher compared to other native populations but similar to introduced populations of similar latitudeEGB was supported by the Spanish Ministry of Science (projects CGL2009-12877-C02-01 and Consolider-Ingenio 2010 CSD2009-00065)

Knowledge of the size-selectivity of fishing gear types is crucial to fisheries management and ecology. The gillnet selectivity of most freshwater fish is poorly known. We caught 694 individuals of eight widely-distributed freshwater fish species (seven cyprinids and the pikeperch, Sander lucioperca) with multi-mesh gillnets in Spanish reservoirs. The SELECT method was applied to fit four different gillnet selectivity models (normal location, normal scale, lognormal, and gamma). The normal scale model (spread proportional to mesh size) had the best fit in four of the eight fish species. Predicted modal lengths for the best fit models are given to describe gillnet selectivity for the eight fish species. Significant variation in the selectivity parameters was explained by simple shape descriptors such as percent girth or percent depth, suggesting that these shape descriptors might be used as a preliminary tool to describe gillnet selectivity for other fish speciesThis study was financed by the Catalan Water Agency (ACA), Government of Catalonia (CT02003134) and the Spanish Ministry of Science and Technology (REN2003–00477