Head Office Press Office
- 10-Sep-2007 - Environment Agency investigates
health concerns in salmon
The Environment Agency is actively investigating
the widespread occurrence of wild salmon
with swollen and bleeding vents.
There has been an increase in the number
of wild Atlantic salmon showing signs of
nematode infestation. The condition is characterised
by swollen bleeding vents (the waste and
reproductive outlets) in female and male
salmon. There is no evidence at present
to suggest the condition causes mortalities
in salmon, or adversely impacts on spawning,
and any affected fish caught should be treated
as normal and can be released following
capture without additional concern.
In England and Wales the situation is being
monitored closely by the Environment Agency
and scientists at the Centre for the Environment,
Fisheries and Aquaculture Science (Cefas),
Weymouth. Similar monitoring is taking place
in Scotland and Northern Ireland.
"We are uncertain at present as to
the exact cause of the inflamed vents,"
explained Environment Agency Fisheries Manager
Godfrey Williams. "There is some evidence
from fish caught to suggest the cause could
be a reaction to the presence of the Anisakis
simplex nematode parasite. However, as Anisakis
are a common parasite of salmon and many
other fish, it remains unclear as to why
these symptoms are now being seen so widely.
"To date there is no evidence the
condition affects spawning or causes mortalities
in salmon, but the situation is being monitored
closely. There is no evidence of the condition
in other marine species, including wild
trout or farmed species of salmon or trout.
The Anisakis simplex is a common parasite
of marine fish throughout the world. Whilst
the parasite can be carried into the freshwater
by migrating fish, it is unable to complete
its lifecycle in freshwater as it requires
the presence of marine invertebrates or
mammals to complete its life cycle. The
nematode has a complex life cycle, with
the adult form infecting seals, whales and
other marine mammals. Wild salmon ingest
the nematode larvae during feeding at sea.
Low incidences of this condition have been
noted in wild salmon in previous years but
the number of cases increased during 2006
and has been noted at their highest levels
so far during 2007. The condition appears
to be widespread and has been reported in
many salmon rivers in England and Wales,
including the rivers Exe, Dee, Taff, Camel,
Tamar Eden, Tyne, Itchen, Ribble, Esk, Exe,
Wye and Lune, and in a number of Scottish
and Irish rivers.
The symptoms are not unusual in individual
fish. What is unusual now is the number
of fish involved and its widespread distribution.
In 2005 5% of trap-caught fish on the River
Dee had the condition. In 2006 that had
risen to 10% (119 individual fish). The
provisional figure for 2007 is 15% to date.
Reports suggest the frequency of occurrence
may be higher in some other rivers.
Both male and female salmon have been affected.
The majority of affected salmon to date
have been freshly-run grilse. However, two-sea-winter
fish displaying the symptoms have also been
reported from a number of rivers. To date
we have not seen these symptoms in sea trout.
Apart from the specific vent symptoms, the
fish generally appear in good condition.
"We have been keeping a close eye
on developments and keeping records so that
we can determine numbers of fish affected
and where these are located. We will continue
to monitor the situation and will report
our findings in due course," continued
Godfrey Williams.
"We have obtained a small number of
fish from the Rivers Eden (2006) and Tamar
(2007) for analysis and post mortem. It
is our intention to obtain additional samples
from a number of rivers in 2007.
"Any additional threat to already
depleted salmon stocks must be of concern.
However, from our observations it is unlikely
that there will be any additional impact
at the individual stock level. There have
been no reports, either last year or this
year, of mass mortalities of salmon. Any
affected fish should be treated as normal
and can be released following capture without
additional concern.
"A number of affected fish were taken
to our hatcheries last winter and all of
these were successfully stripped of their
eggs (and the eggs developed normally).
In addition, an affected salmon tagged on
the River Dee in 2006 was recaptured this
spring as a kelt. On inspection this fish
appeared to have spawned successfully in
the wild and had recovered condition. It
appears the affected fish will survive to
spawning time and will spawn successfully
in the wild or in hatcheries.
"We will continue to monitor the situation
over the coming months. As well as recording
all incidents we are made aware of we will
obtain additional samples of fish for post-mortem
and analysis. What we want to do now is
to work with colleagues in Cefas to try
and find out what is causing symptoms to
appear in so many fish. In addition, we
will share experiences and knowledge with
our counter-parts in Scotland and Ireland
and report our findings in due course."
The Environment Agency cannot provide advice
on the consumption of fish. The Food Standards
Agency supervises a raft of hygiene legislation
applying to food businesses that protects
consumers from the risk of parasitic infection
from consuming fish. The FSA advices cooking
fish for at least two minutes at a temperature
of 70C will kill any parasites, including
nematodes. Further advice may be obtained
from the FSA website at www.food.gov.uk.
