RATIONALE: Dorsal white muscle is the standard tissue analysed in fish trophic studies using stable isotope analyses. However, sampling white muscle often implies the sacrifice of fish. Thus, we examined whether the non-lethal sampling of fin tissue can substitute muscle sampling in food web studies. METHODS: Analysing muscle and fin d15N and d13C values of 466 European freshwater fish (14 species) with an elemental analyser coupled with an isotope ratio mass spectrometer, we compared the isotope values of the two tissues. Correlations between fin and muscle isotope ratios were examined for all fish together and specifically for 12 species. We further proposed four methods of assessing muscle from fin isotope ratios and estimated the errors made using these muscle surrogates. RESULTS: Despite significant differences between isotope values of the two tissues, fin and muscle isotopic signals are strongly correlated. Muscle values, estimated with raw fin isotope ratios (1st method), induce an error of ca. 1% for both isotopes. In comparison, specific (2nd method) or general (3rd method) correlations provide meaningful corrections of fin isotope ratios (errors <0.6%). On the other hand, relationships, established for Australian tropical fish, only give poor muscle estimates (errors >0.8%). CONCLUSIONS: There is little chance that a global model can be created. However, the 2nd and 3rd methods of estimating muscle values from fin isotope ratios should provide an acceptable level of error for the studies of European freshwater food web. We thus recommend that future studies use fin tissue as a non-lethal surrogate for muscle

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Morphological adjustment mechanisms and controls of small urban rivers are rarely studied especially in France. We propose an original hydrogeomorphological approach based on a detailed study of a whole catchment using field data acquired systematically all along the river: (i) channel cross‐sections; (ii) riffle‐pool sequences and (iii) obstacles to flow and rainwater drainage pipes. The entire length of the river was surveyed and the channel geometry (depth and width at bankfull) was measured on a cross‐section every 180 m or at each riffle (depending on which of the two intervals happened to be the shortest). The 357 transects thus established constitute as many elementary units of measurement (EUM) of the hydrographic network. Nine hydromorphological variables were used as a basis to classify the profiles (principal component analysis/hierarchical clustering analysis). The types were compared with 12 anthropogenic constraining variables to explain longitudinal morphological variability and to link morphology to pressures on this scale. The results showed an average incision of 0.50 m (locally over 1 m), an average widening of nearly 1 m (locally over 3 m), and heterogeneous distribution of the riffle‐pool sequences (although not complete disappearance). Systematic analysis of within‐channel forms revealed high morphological diversity, the absence of a linear relationship between the rate of urbanization and incision/erosion, and the absence of longitudinal changes in response to urbanization. The constraints identified are commonly observed in urbanized basins, but the variety of responses to the constraints makes it difficult to understand the system as a whole and prevents uniform ecological restoration along the entire river.