ECHO and Infectious Disease
There are many different causes of disease in carp,
including nutrition, water quality and a multitude of infectious
agents such as bacteria, viruses and parasites. ECHO are particularly
concerned with infectious diseases and the impact caused by newly
stocked fish to resident populations in the British Isles.
Infectious diseases, depending on their cause can
have either severe, acute impacts on the carp population or more
long term and chronic effects. Those known to fit the first category
include viruses, which under the right conditions can multiply very
rapidly and bring about severe disease symptoms or death in a matter
of weeks, possibly even days.
Spring Viraemia of Carp (SVC)
The best known carp virus and one which been responsible for many
major carp kills in the British Isles. It is related to fish imported
from mainland Europe where it is classed as endemic. It is a rhabdovirus
and can also affect, and be carried by, many other fish species
including; crucian carp, goldfish, grass carp, silver carp, bream,
roach, tench, barbel and wels catfish.
It usually occurs in the spring/early summer with rising water temperatures,
usually up to ~15 degrees C and may kill the majority of carp, although
Clinical signs vary greatly from one case to another but may include:
lethargy, pop-eye, darkening of skin, thickening of swimbladder,
haemorrhaging in internal organs and general swollen appearance.
Koi Herpes Virus (KHV)
A recently discovered carp virus which originally was associated
with big kills of koi carp in the ornamental industry. It is a very
virulent and extremely contagious herpes virus which is capable
of causing mortalities of 90% of the affected carp. It is said to
be most pathogenic at water temperatures between ~ 23-27 degrees
C although it has so far been reported to be capable of multiplying
at temperatures of 17 degrees C. It is possibly due to this temperature
range that it is koi carp that have been most affected by this disease
KHV is most characteristic by causing massive damage
to the gills of the affected carp. It hasn't yet been reported in
wild carp populations in the British Isles, however it's contact
with our fisheries is inevitable due to introductions of domestic
koi and carp…!
Spring Carp Mortality Syndrome (SCMS)
This is a disease which has been studied by the Environment Agency
for several years. It is has long been associated with an infectious
agent and is strongly related to new introductions of fish to resident
carp stocks. However the causative agent is yet to be confirmed.
It is considered likely to be a virus, the type of damage it causes
to affected carp having many similarities with KHV (severe gill
damage), the major difference being the temperature range at which
it kills fish at, generally up to ~15 degrees C.
SCMS causes kills of ~15-90% of the carp population.
Fish kills caused by SCMS are most likely to occur after a fish
introduction and are commonly linked with carp supplied by people
who deal in fish.
The previous listed three infectious agents are likely to directly
cause major kills of British carp.
Infectious agents and biggest threats are:
SVC: illegally imported fish.
KHV: ornamental/ aquatic trade fish introductions.
SCMS: fish supplied by fish dealers.
The above also applies to fish which have been
exposed to such listed fish. This is the reason as to why people
that deal with fish who do not maintain good disinfection procedures
between handling fish or who mix fish represent potentially dangerous
stocks. Fish populations carrying infectious diseases may contaminate
others fish stocks handled by such persons and continue the spread
of the disease.
The biggest fish kill risk is through fish introductions. Always
consider these risks before you introduce new fish to your water.
If you must stock, follow the guidelines the Environment Agency
produce called "Buyer Beware," this gives ten points to
consider before you go ahead with your fish introduction. This leaflet
is available by contacting your local EA area office.
The safest and most sustainable solution is to
try and get your fish to spawn naturally to provide natural recruitment
of carp into the population.