Münderle, M.; Sures, Bernd; Taraschewski, H.:

Influence of Anguillicola crassus (Nematoda) and Ichthyophthirius multifiliis (Ciliophora) on swimming activity of European eel Anguilla anguilla.

In: Diseases of aquatic organisms : international journal., Jg. 60 (2004), S. 133-139
ISSN: 0177-5103
Zeitschriftenaufsatz / Fach: Biologie
We investigated the swimming activity of 70 European eels Anguilla anguilla in relation
to natural infection with 2 parasite species: the eel-specific swimbladder nematode Anguillicola
crassus and the non-specific skin and gill protozoan Ichthyophthirius multifiliis. We measured how
long individual eels exposed to a water current in a swimming channel with a steady-stream profile
could withstand the water current. The parasites affected the swimming behaviour of eels in different
ways. The maximum period of time the fish were able to swim against the current was not correlated
with infection by A. crassus. In contrast, infection with I. multifiliis reduced the swimming time.
The protozoan has a higher pathogenicity than the swimbladder nematode, at least in closed systems,
where I. multifiliis is able to spread within a few days. Reduction in swimming capacity after infection
with the ciliate averaged 47 % compared to capacity prior to infection. Thus, our results do not
support the previously suggested strong negative relation between swimming activity of eels and
intensity of A. crassus infection, at least in the short-term. However, there are indications in the
literature that the pathological effects of A. crassus on the eel swimmbladder may involve a higher
energy demand, possibly manifested in a prolonged spawning migration. As a result, eels heavily
infected with this parasite may arrive too late at the spawning site to participate in mating. This could
ensure a selection of ‘good genes’.

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