Stable isotope analyses provide new insights into ecological plasticity in a mixohaline population of European eel.

Recent studies have shown that anguillid eel populations in habitats spanning the marine-freshwater ecotone can display extreme plasticity in the range of catadromy expressed by individual fishes. Carbon and nitrogen stable isotope analysis was used to differentiate between European eels (Anguilla anguilla) collected along a short (2 km) salinity gradient ranging from <1 per thousand to approximately 30 per thousand in Lough Ahalia, a tidal Atlantic lake system. Significant differences were recorded in mean delta13C, delta15N and C:N values from eels collected from fresh, brackish and marine-dominated basins.