24/05/2005 - The Environment
Agency has detected antibodies to tench rhabdovirus
in fish in seven rivers in England, indicating
that the fish have been exposed to tench rhabdovirus
during their lifetimes. While these findings
show that the disease is more widespread than
previously thought, no fish mortalities have
been reported since 1999 and so the virus
may not be a serious risk to fish populations.
This virus was previously believed not to
be widespread in the wild, having only been
detected twice in England and Wales. In 1999,
it caused fish mortalities in five waters
which had all been supplied with bream from
a single source in Northern Ireland and in
2004 it was found at the Agency’s Calverton
Fish Farm. Both Calverton and Leyland Fish
Farm were cleared and disinfected as a precaution.
Restocking of both farms has started. To
prevent re-infection, the Environment Agency
has been testing fish for exposure to tench
rhabdovirus from rivers and stillwaters before
using them as broodstock.
Using non-lethal blood tests, developed by
the Centre for Environment, Fisheries and
Aquaculture Science (CEFAS) as a result of
the investigation at Calverton, Environment
Agency fisheries scientists have been screening
potential broodstock from thirteen rivers
and eight stillwaters across England. They
found evidence that the virus may have been,
or may still be present in, seven of the thirteen
rivers. Those with positive results are;
River Trent in Nottinghamshire
River Teme in Worcestershire
River Nidd in Yorkshire
River Wharfe in Yorkshire
River Witham in Lincolnshire
River Douglas in Lancashire
River Wye in Derbyshire
Not every test undertaken, however, has proved
positive. Samples taken from the Ribble and
the Pennington Flash in Lancashire, the Cam
in Cambridgeshire, the Test in Hampshire,
the Bain in Lincolnshire and eight stillwaters
in northern England have all tested negative.
The Dover Beck, which is immediately downstream
of Calverton Fish Farm, has also tested negative.
Nigel Hewlett, Senior Fish Health Scientist
at the Agency, said “We do not know how serious
these latest findings are. They do suggest
that the virus may be more widespread than
we originally thought, but, as it does not
appear to have caused any fish mortalities
in the wild since 1999, it may not prove to
be a serious risk to fish populations.“
Where tench rhabdovirus outbreaks have been
encountered in the past, they have resulted
in acute and significant fish kills, albeit
these have been in exceptional circumstances
which may have rendered the fish more susceptible
to the disease. No such incidents have been
recorded from any of the rivers recently tested.
Dafydd Evans, Environment Agency Head of
Fisheries, said: ‘All these rivers are extremely
valuable and popular fisheries, and we have
no evidence that the virus has had an impact.
More work on the disease is needed, however,
and we will be working closely with CEFAS
to get a better understanding of its distribution,
what impact it can have on wild fish stocks
and what risk this poses to fisheries.
‘We do not intend to impose any immediate
restrictions on fish movements, but we would
advise fishery owners and anglers to take
the usual precautions – always take care when
buying fish for restocking.’
