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The applicability of an enzyme-linked immunosorbent assay (ELISA) for the detection of anguillicolosis in feral eels was examined using a crude antigen preparation from the body wall of adult Anguillicola crassus. The screening consisted of samples from 100 feral European eels Anguilla anguilla. As a reference the actual status of infection was determined by dissection of the eels' swimbladders. The ELISA results were compared with a background value calculated from the results obtained from 43 non-infected farm eels. The screened samples had a high prevalence of A. crassus (83%); however, the specificity and the negative predictive value of the ELISA were low compared to the high positive predictive value. Nonetheless, the reproducibility (precision) of the test was satisfactory, and for the non-infected reference group specificity was 97.7%. Although the ELISA, as used in the present study, is not applicable for diagnostic purposes, it represents a useful tool for the investigation of the specific humoral immune response of eels against A. crassus under controlled experimental conditions. Immunoblots using crude antigen preparations from different parts of adult A. crassus as well as a crude somatic third-stage (L 3 ) antigen preparation illustrated that only antigens associated with the body wall of adult A. crassus are potentially suitable for diagnostic purposes. Despite the fact that antibodies against Raphidascaris acus cross-reacted with 3 body wall antigens of A. crassus, the most encouraging results were obtained with the antigen preparation from the outer cuticle of adult A. crassus which yielded a conspicuous, broad band at about 100 kDa.

A humoral immune response of the European eel Anguilla anguilla elicited by an experimental infection was demonstrated for the first time against the swimbladder nematode Anguillicola crassus. Eels were experimentally infected once or repeatedly and the antibody response was observed over a period of 325 d. Specific antibodies against A. crassus in the peripheral blood of the eels were measured using an ELISA and the immunoblot technique. Anti -A. crassus antibodies were first observed 8 wk post infection, and appeared to be independent of both the number of infective third stage larvae (L 3 ) administered and the frequency of administration. However, individual eels showed great differences in the course of the antibody response. The late appearance of antibodies in the peripheral blood supports the hypothesis that not the invading L 3 but rather the adult parasites elicit the production of specific antibodies. A stage-specific antibody response against the L 3 was not observed. Main antigens are located in the body wall, especially in the gelatinous outer cuticle, of adult A. crassus. KEY WORDS: Anguilla anguilla · Anguillicola crassus · Humoral immune response · Experimental infectionResale or republication not permitted without written consent of the publisher

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