Population biology of Anguillicola crassus in the final host Anguilla anguilla

Abstract

Eels were sampled twice a month (March 1990 through March 1991) at the Kolenhaven (Albertcanal, Genk, Belgium) and examined for Anguilljcola crassus nematodes in the swimbladder. Averaged over all samples, 90.2 % of the 345 eels were infected with a mean intensity (averaged for all stages) of 17 nematodes. Thirty-one percent of all nematodes, which were adult worms or their remnants, were present in the swimbladder lumen, while the other 69 % which consisted of the third or fourth larval stage and preadults were found in the swimbladder wall No clear seasonal fluctuations in parasite prevalence or mean intensity were observed Both L3-larvae and mature adult worms were present throughout the year. Eggs or L2-larvae were observed in 41 % of the infected eels. This presence showed no seasonal pattern, though it was positively correlated with eel length. masslve concentrations of L2-larvae were only found in eels bigger than 40 cm. A positive but weak correlation between eel length and number of adult nematodes in the swmbladder was significant, while no correlation was found between eel length and total parasite burden.