| Summary: | The carrier status and possible elevated tolerance of the signal crayfish
(Pacifastacus leniusculus) against the crayfish plague disease agent
(Aphanomyces astaci) has been speculated for several decades. We
studied experimentally the responses of the signal crayfish from two Finnish populations
against the crayfish plague infection by using two crayfish plague isolates with differing
virulences; the highly virulent PsI-isolate and the mid virulent As-isolate. The studied
signal crayfish came from two origins: the wild Leppävirta population and the Raukola
farmed population of mixed genetic background. Both test groups were infected with
A. astaci isolates using the challenge of 10 000 spores
mL-1. The
isolates were PsI-Puujärvi (UEF8866-2) from Lake Puujärvi signal crayfish (year 2003) and
As-Kivesjärvi (Evira6462/06) from Lake Kivesjärvi noble crayfish (year 2005 epidemic) in
Finland. The crayfish were sampled prior to the experimental challenge with A.
astaci to evaluate their A. astaci carrier status. The
mortality, molting, feeding activity and other behavior of the crayfish were followed
during the experiment. We observed increased mortality of the infected groups, related to
the molting in some cases, and delayed molting. The impacts of the intense crayfish plague
infection on the signal crayfish were clear and the studied populations showed differences
in their reactions that are potentially explained by differing physiological conditions
and different molt cycle phase. The results show that infection of both tested crayfish
plague genotypes affects signal crayfish and is likely one of the main reasons behind
losses among signal crayfish populations.
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