Ageing of fish from their calcified structures is the basis of most of our present-day fisheries management decisions. The problem of ageing is especially difficult in the eel Anguilla anguilla. A large number of ageing techniques and interpretations are in current use, and the results obtained using different methods may vary considerably (Moriarty and Steinmetz, 1979; Moriarty, 1983; Vøllestad, 1985; Vøllestad and Næsje, 1988). At the 1985 meeting of the EIFAC (European Inland Fisheries Advisory Commission) Working Party on Eel in Perpignan it was agreed that a review of ageing studies in the last 10 years should be undertaken, and that the review should include proposals for future work. A circular letter was sent to all attending the 1985 meeting of the Working Party asking for precise information on the applied ageing methodology. This review collates information on the ageing techniques commonly in use today based on these replies as well as on published descriptions of methods. Where appropriate we describe methods used on species other than A. anguilla.
All eel workers use saggital otoliths, and no workers routinely use structures such as scales, fin rays, vertebrae or opercula. Scales have since long been discarded as unsuitable for ageing eels (Smith and Saunders, 1955; Jellyman, 1979), a result recently confirmed by Dekker (1986) using tetracycline labelling. Very little work, if any, seems to have been done on the vertebrae, fin rays and opercula.