Page 76 - Koi Net - On-Line Koi Magazine - Issue 36

RESISTANT FLUKES

Dr. Fiona Macdonald, BVMS MRCVS
Managing Director, Fish Treatment Ltd

Although, unfortunately, resistance to treatments
is a common situation with all parasites, it can be
very challenging both for Koi keepers trying to
protect their stock and treat infected fish, and for
veterinary pharmaceutical companies who are
always trying to develop new effective treatments,
with a limited range of available anti-parasitics.
Right:
OVER THE Over the last 2 years we have seen a dramatic Gyrodactylus sprostonae.
increase in resistant flukes which so far seem to be
LAST 2 YEARS varying species of live-bearing flukes, although Below:
Gyrodactylus sprostonae
WE HAVE SEEN we cannot rule out the possibility of resistance attached to the host.
appearing in egg-laying flukes either. I tend to group
A DRAMATIC flukes by how they reproduce rather than where you
find them on your fish – hence gill flukes are egg-
INCREASE IN laying, whereas skin flukes are live-bearing with
RESISTANT multiple generations inside some of them. However,
just to make diagnosis a little more challenging,
FLUKES these fluke can migrate between the skin and the
gills – hence my distinction by reproduction method.

Although initial studies at the start of this problem
suggested that only one resistant fluke species,
Gyrodactylus sprostonae, was involved, as the
problem has developed it is clear that there are other
new resistant flukes now appearing on the scene.
Although misuse of treatments such as persistent
underdosing can lead to resistance, there is a strong
likelihood that the majority of these resistant species
will have been imported. Also microscopic
identification of these parasites is not always
straightforward.

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