Validation of the occurrence of the American eel Anguilla rostrata (Le Sueur, 1817) in free-draining European inland waters

The screening of 2,735 eels from European waters and aquaculture farms was conducted using mitochondrial Cytochrome b and 16S rRNA gene fragments amplified by polymerase chain reaction. Reaction products were either sequenced directly or subjected to analysis using restriction fragment length polymorphism which resulted in species-specific restriction patterns. Beside the expected European eel, Anguilla anguilla (Linnaeus, 1758), the American eel, Anguilla rostrata (Le Sueur, 1817), was also identified in samples from both aquaculture (N = 40 out of 1,025) and from natural waters (N = 44 out of 1,710). The life stages of American eels identified from several German waters draining to either the Baltic Sea and the North Sea ranged from elver to silver eels. This indicates that stocking with glass eels or elvers must have occurred several times most likely in the period from 1998 to 2002. The application of a fast and precise method for species identification and genetic monitoring of eels delivered for stocking is therefore essential for maintaining the autochthonous species composition in future.