Fishery Management

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 generally 20-50%.
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 so far….

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.