EFFECTS OF EXPERIMENTAL INFECTIONS WITH DIFFERENT DOSES OF ANGUILLICOLA-CRASSUS (NEMATODA, DRACUNCULOIDEA) ON EUROPEAN EEL (ANGUILLA-ANGUILLA)

To study the effects of various doses of Anguillicola crassus in prima ry infections, parasite-free European eels were orally infected with d oses of 0, 1, 5, 10, 20 or 40 third-stage (L3) larvae. The eels were e ither killed and examined for parasites and lesions after 56 days, or reinfected with 20 L3 larvae to study the effect of primary infection on resistance. Reinfected eels were killed and examined on Day 112. Bl ood samples were collected weekly and examined in an enzyme-linked imm unosorbent assay (ELISA) to detect antibodies against adult parasite c uticula antigen. The mean percentage of A. crassus recovered from eel swimbladders ranged from 14 to 20% on Day 56 and from 9 to 26% on Day 112. There was no significant relation between the proportion of recov ered parasites and the primary and/or secondary infection dose. Furthe rmore, the higher the dose, the more severe were the haemorrhages and pigment spots seen in the swimbladder. Reinfected eels had significant ly more severely thickened swimbladders, haemorrhages in the swimbladd ers and congestion of blood vessels in the swimbladders. Results of th e ELISA showed that the eels developed no detectable antibody response against A. crassus. We concluded that under the given stressful exper imental conditions, although eels develop pathological signs after pri mary and secondary infection with A. crassus, they do not develop an a ntibody response or resistance.