SCANNING ELECTRON-MICROSCOPIC ANALYSIS OF ANNULUS MICROSTRUCTURE IN OTOLITH OF EUROPEAN EEL, ANGUILLA-ANGUILLA

To validate the yearly periodicity of annulus formation in the otolith of the eel, the structure of annuli in otoliths the European eel, Ang uilla angulla, stocked for 7 and 12 years in Lake Ommen on the east co ast of southern Sweden, was examined. The population was stocked from elvers imported both from France (Bay of Biscay) in April 1979 and Eng land (River Severn) in March-April 1984. The microstructure of an annu lus consisted of single, double and/or composite rings depending on th e location in the otolith. The counts of annuli in otoliths of these e els were approximately consistent with the expected age. However, supe rnumerary false annuli and/or annulus underestimation frequently occur red. The methodology for annulus discrimination with light and scannin g electron microscopes is described.