Anguillid Herpesvirus (AngHV-1, formerly known as Herpesvirus anguillae or HVA) was first detected in the summer of 2009 following investigations into an eel specific mortality by staff at our National Fisheries Laboratory. This was the first confirmed outbreak of AngHV-1 in wild eels in the UK. The virus has since been confirmed at other river and still water fisheries in England following large scale losses of eels. Efforts are underway to improve understanding of this virus, as well as other important viral diseases of European eels.

What does AngHV-1 do?

Eels infected with AngHV1 can develop a range of disease signs and symptoms. Diseased eels may appear lethargic and swim near the surface or the water's edge. They may have reddened fins and a mottled appearance to the skin.

The main damage caused by this virus is to the gills, with severe necrosis (cell death) and loss of normal gill structure.

These changes are often seen in combination with bacterial and fungal infection. The internal organs can also be affected with inflammation and further necrosis, leading to organ failure, debilitation and death.

A newly discovered viral disease affecting carp fisheries

Between April and October 2012, National Fisheries Laboratory (NFL), were notified of four unusual carp mortalities in the south east of England. All four waters were within a 5 mile radius and shared similar characteristics of lethargic fish and significant losses. In November 2012, a similar case in the midlands was reported. Laboratory investigations resulted in the detection of Carp Edema Virus (CEV). These represent the first records of this virus in UK carp fisheries. Work is underway with virologists at Cefas to progress our understanding of this virus and the risk it poses to our fisheries.

Effective management of serious fish diseases relies on prompt responses to the detection of new pathogens. To minimise the risk of disease transfer to other fisheries, we have placed fish movement controls on all infected waters. These will remain in place until we have the necessary information to fully assess the distribution and importance of the virus. This decision is supported by the fisheries involved, Cefas and Defra.

What do we know about this virus?

The virus detected from the mortalities in England is very similar to the one responsible for diseases of koi carp in Japan. These were known as Carp Edema, Viral Edema of Carp and Koi Sleepy Disease, but are now believed to be caused by the same virus. It is not clear whether the UK virus shares the same characteristics and causes the same disease problems as those reported in Japan. Detailed laboratory examinations conducted by NFL, Brampton have revealed a range of other pathogens in the fish infected with CEV and also, notable environmental stressors at some of these fisheries, making it difficult to assess the importance of the virus alone.

What fish are susceptible to CEV?

To date, CEV has only been reported in common carp and its ornamental variants like koi carp and ghost carp. No other fish species have been associated with this virus in our fisheries, and in the waters sampled by our field-based fisheries teams, no other species have been visually affected.

How widespread is CEV

Viruses can be very hard to detect, especially if fish appear healthy. Our knowledge of viruses is also limited by the tools available to detect them. It is feasible that CEV is widespread in freshwater fisheries and work is underway to establish whether there are any factors linking affected waters. Until the distribution of CEV is established, caution must be taken to prevent further spread.

What are the main signs of CEV?

Carp infected with CEV usually display two main characteristics. The first is lethargy, or 'sleepy' behaviour, with carp congregating around the margins and becoming increasingly unresponsive. The second is severe gill pathology, with clubbing of the gill filaments, hyperplasia, inflammation and cell death. Other organ changes have been associated with CEV, although these are not always seen.

It is important to realise that lethargy and gill damage can be caused by a wide range of infections and environmental factors. As such, serious fish mortalities require detailed investigations combining laboratory examinations and comprehensive assessments of fishery conditions, water quality and management practices. This information is vital to identify possible causes and rectify any fish disease problem.

What is carp pox?

Fish infected with carp pox have distinctive white, waxy lesions that appear during the low temperatures of winter and early spring. The lesions tend to reduce as temperatures rise in the summer.

It is caused by a virus known as Cyprinid Herpesvirus-1. It is a common disease of common carp, but can affect all varieties of carp. It may affect other cyprinids such as barbel, bream, crucian carp and rudd. It is a long-lasting, but normally non-fatal skin disease which leads to the abnormal multiplication of skin cells. Fish infected with carp pox are thought to be infected for life, but the disease only occurs at certain times of the year when conditions are right.

What does carp pox do?

Carp pox is usually more unsightly than it is harmful to the fish. The lesions can develop all over the external surface of the fish, though are commonly on the fins. At first the lesions are flat, firm, smooth and translucent, but they can grow thicker on the body. They are milky to greyish-white in colour and may cause scarring. In extreme cases individual lesions can grow and join, covering a large proportion of the body surface, but rarely the whole fish.

The disease will not normally kill the fish. If the infection only attacks small areas of the body, then the fish will not be distressed. However, lesions covering the mouth or gills may impede feeding or respiration, causing greater distress. There is evidence to suggest that the number of mucus producing cells of the fish become reduced. In severe cases, normal growth of the fish is affected and they may become thin and the skeleton damaged.

Minimising the problems with carp pox- what can I do?

Carp pox is one of the easiest conditions to spot on fish, but unless it is present in high numbers or large lesions are present, it should not be of immediate concern.

There is no treatment for carp pox. Good fishery management is the best way to avoid disease outbreaks. Water temperature is a key factor to carp pox infections occurring, although fish are more likely to experience problems when they are stressed or debilitated. The following measures will also be beneficial to a fishery: 

Reducing stress within the fish population

Carp pox is more likely to infect fish when they are stressed. Stressors include high stock densities, poor habitat and poor water quality.

Careful management of stock levels

Keeping your stock densities low is important to avoid carp pox infections. High fish stocks cause stress to the fish making them more susceptible to infection.

Regular monitoring of water quality

Decreasing water temperatures are often a cause of carp pox. The temperature of the water cannot be controlled, but regular monitoring of water quality (dissolved oxygen content, pH and ammonia) that can be managed is essential to prevent problems within a fishery.

In 2018, Eel Virus European X (EVEX) was detected during an eel specific mortality investigated by staff at our National Fisheries Laboratory. This was the first detection of this virus during a mortality event of wild eels in England. Efforts are underway to improve understanding of this virus and its distribution. In the meantime, fish movement restrictions are in place to help limit the spread of this important eel pathogen.

Eel Virus European X (EVEX)

Eel Virus European X is a rhabdovirus that infects all species of eel in freshwater. It was first detected in 1977 from European eels imported into Japan from France. Since then the virus has been detected throughout Europe, as well as parts of Asia, Africa and Oceania. EVEX is regarded as one of the most important viruses of the European eel that has the potential to cause mortality and migration failure.

What EVEX does

Whilst EVEX has been detected in outwardly healthy eels, it has also been associated with significant mortalities. Diseased eels can appear lethargic and show signs of emaciation, skin lesions and haemorrhaging. Infected eels can die from severe haemorrhagic changes that appear across the skin, fins and throughout the internal organs.

Importance of EVEX

The European eel population has declined in recent years. Whilst the cause for this is unclear, there is growing awareness of the importance of diseases, both in the decline of the eel stock and its recovery. Eels have a long and complicated life cycle that involves a lengthy spawning migration to the Sargasso Sea. This is a stressful period during which immune responses are suppressed and susceptibility to diseases is increased. Experimental studies have shown that eels infected with EVEX suffer reduced swimming ability and are likely to die before reaching the Sargasso Sea. 

Status of EVEX and other eel viruses in England

Very little is known about EVEX in wild eels in England. The recent detection of the virus during mortalities of eels in river catchments in East Anglia represents the first record of the virus in the wild. At present the most frequently detected virus of wild eels in England is Anguillid herpesvirus (AngHV-1), which was first detected 2009 following mortality investigations conducted by staff at our National Fisheries Laboratory. AngHV-1 has since been associated with eel mortalities at a number of other sites in England, with further outbreaks confirmed in both still waters and rivers. High temperatures and barriers to migration are thought to be important triggers for this disease. A low-level infection of an Aquabirnavirus, suspected to be Eel Virus European (EVE) was also detected in an eel specific mortality during 2018. Further work is needed to understand the role of these viruses in determining the health of UK eels.

What the IFM are doing

We continue to monitor the status of eel viruses nationally through our incident response. We are also working with fishermen and partner organisations to raise the profile of eel health and promote reporting of any fish health issues immediately to the Environment Agency. Following the recent detection of EVEX, we have issued biosecurity guidance to eel fishermen, to help reduce the risk of disease transfer between catchments.

We are currently working with colleagues at the Centre for Environment, Fisheries and Aquaculture Science (Cefas) to develop new diagnostic tools so we can test for EVEX from blood samples. This will allow us to assess the distribution of this virus during our routine monitoring activities, or prior to stocking, without the need to sacrifice eels. This information will help to determine the distribution and impact of these viruses in our wild eels and will provide context to the recent mortalities we have investigated

What you can do

Please report any signs of dead or dying eels to us immediately. If you see any fish dying or in distress please contact our incident hotline - 0800 80 70 60. Prompt reporting of problems can allow us to respond quickly and effectively to disease outbreaks in fisheries

What is KHV?

Koi herpesvirus (KHV) is a virus that infects common carp (Cyprinus carpio) and its ornamental varieties, such as koi and ghost carp. Since being first reported from Israel and the USA in 1998, KHV has spread rapidly through the international fish trade, and it is now one of the most important viral diseases of carp worldwide. 

KHV disease was confirmed in English carp fisheries in 2002, following mortality investigations at a still water. The virus has since spread throughout England. To date, National Fisheries Services (NFS, Brampton) have investigated over 100 cases of KHV, providing support and advice to avoid future losses and get fisheries back on track. The virus is now widespread in England and often triggered by intensive fishery management practices.

What does KHV do?

KHV is an important pathogen of carp, capable of causing large scale mortality. Fish with KHV disease typically show signs of lethargy, respiratory distress and erratic behaviour. Fish may linger at the water surface, congregate in the margins or collect around water inlet points. Clinical signs of KHV can vary but include severe gill pathology, such as patches of necrosis (cell death) and erosion. These are frequently accompanied by fungal, bacterial and parasitic infections. Other signs of KHV disease include sunken eyes and changes to the internal organs.

What triggers KHV in your fishery?

KHV is usually triggered by two main factors, temperature and stress. Viruses often have temperature ranges in which they become more active and pathogenic. Outbreaks of KHV generally occur in late spring and summer when water temperatures are between 16°C and 28°C. Outside of these temperatures, the virus may lie dormant without causing problems.

Stress is also a key factor that triggers KHV. There are many factors that can increase stress within the fish population including poor environmental conditions, overcrowding and excessive handling. When temperatures are favourable any increase in stress can trigger a disease outbreak. KHV outbreaks most commonly occur in intensively managed carp fisheries with very high stock densities. Recent stocking can also increase disease risks, although the virus can be present in a fishery for some time before causing problems.

How is KHV spread?

KHV has spread rapidly following the import of infected fish and is now widespread in England. Fish stocking poses the greatest risk of introducing the disease to your fishery. The difficulty is detecting the virus in healthy fish, as carp may carry the virus without showing signs of disease. It is also possible to transfer the virus on wet fishing tackle, nets and boots, or by the transfer of infected water. Good fishery management and biosecurity are critical in minimising the risk of transferring KHV.

How is KHV confirmed?

KHV disease can only be confirmed through specific laboratory tests. It is not possible to confirm KHV from the bank side or by external examinations alone. Lethargy and gill necrosis can be caused by many different factors including poor water quality, toxins, algae and diatom blooms, parasites, bacteria and fungi. It is not uncommon to find a range of different infections and problems during KHV outbreaks. Confirming the cause of any disease outbreak requires detailed post mortem examinations combined with assessments of environmental conditions and fishery management practices.

Is KHV a controlled disease?

Since the detection of KHV in carp fisheries in 2002, control measures have been in place to limit the spread of the virus in England. These were initially placed by the Environment Agency under Section 30 of the Salmon and Freshwater Fisheries Act, 1975. This involved movement restrictions on all waters where the virus was confirmed.

In 2007 KHV became a Notifiable disease under the Aquatic Animal Health (England and Wales) Regulations. This made it a legal obligation to report suspicion of the disease in any farmed or wild fish to the Fish Health Inspectorate (FHI). We support the FHI in controlling notifiable diseases and ensure that all carp mortalities investigated at NFS, Brampton are tested for KHV.

What about other viruses?

There are many different viruses that can cause disease in fisheries. Examples include the notifiable disease Spring Viraemia of Carp (SVC) and the recently detected Carp Edema Virus (CEV). CEV is a non-notifiable disease that poses additional risks to our carp fisheries. For more information on CEV and our controls to protect fisheries please see our factsheet 'Carp Edema Virus and other viral diseases of carp'.

What happens if KHV is found at your fishery?

If KHV is confirmed at your fishery a member of the FHI will contact you and may place movement controls on your water and enforce specific biosecurity measures. You will be fully informed of any actions or restrictions and we will work with you to ensure the best outcome for your fishery. As most KHV outbreaks are triggered by environmental conditions and intensive fishery management, there are things that can be done to limit losses and prevent a re-occurrence of disease.

A common parasite in still waters, Argulus can cause significant irritation and damage to fish. They feed on the fish's skin and mucus, leading to inflammation and secondary infections

Is a disease in fish is caused by digenean trematode parasites, specifically the larval stages (metacercariae) encysted in the skin, fins, or muscle tissue. These cysts, which contain the parasite, are surrounded by a black pigment produced by the fish, hence the name "black spot". While not generally harmful to the fish's health, they can make the fish appear less appealing for consumption

• Cause: The disease is caused by a complex life cycle involving snails, fish, and fish-eating birds. 
• Appearance: The black spots are actually tiny, encysted larval trematodes (flukes). 
• Impact on fish: The parasite does not cause significant harm to the fish's health, and they can continue to grow and thrive despite the infection. 
• Impact on humans: While the parasites are harmless to humans, they can make the fish appear unappetising to eat. 
• Control: There's no specific method to eliminate black spot disease, but skinning infected fish will remove the cyst
• Preventative Measures: Maintaining good water quality, proper husbandry practices, and biosecurity measures can help prevent outbreaks of parasites in both wild and captive fish. 

Reporting:

Any suspected outbreaks of fish disease, including parasite infestations, should be reported to Highbridge angling association

Chilodonella species are single-celled, microscopic organisms. They are ciliates, meaning that their bodies possess small hair-like structures called cilia. Most are free-living and are not parasites. However, Chilodonella hexasticha and Chilodonella piscicola are external parasites (ectoparasites) that infect a wide range of freshwater fish species.  They are found on the skin and gills of fish, and can multiply rapidly in both cold (5-10°C) and warm water. Both can be very damaging to fish and cause serious disease. 

Causes and Prevention:

• Stress and Poor Water Quality: Chilodonella thrives in poor water conditions, including high ammonia, nitrite, and nitrate levels. 
• Overstocking: Overcrowding in ponds and aquariums increases the risk of infection. 
• Inadequate Filtration: Proper filtration, including the use of activated carbon, is crucial for maintaining good water quality and preventing Chilodonella outbreaks. 
• Stressful Events: New fish introductions, temperature changes, and aggressive fish can weaken the immune system and make fish more susceptible to infection

Gyrodactylus sprostonae is a gill monogenean ectoparasite that is causing significant mortality in adult carp within UK fisheries. It is an emerging pathogen, particularly in recreational carp fisheries. The parasite is also known to infect juvenile carp, though the infection tends to clear up within about 40 days without causing clinical signs or death

• Target Host: Primarily affects adult common carp (Cyprinus carpio). 
•  Infection Location: Primarily infects the gills of fish. 
• Spread: Can be transmitted through direct contact with infected fish or by parasites surviving in damp environments for a few days, according to GOV.UK. 
• Mortality: Can be a major cause of mortality in adult carp, according to the Institute of Fisheries Management. 
• Impact on Juvenile Carp: While juveniles can be infected, they tend to clear the infection within about 40 days without causing clinical signs or death,

Ichthyobodo necator causes damage to the gills and skin of fish. Infected fish can lose condition, become emaciated and be very lethargic. These symptoms can be seen in fish with only a light infection. The attachment and feeding of Ichthyobodo necator causes severe damage to skin and gill cells

specifically Piscicola geometra, are common parasitic worms that attach to fish and suck their blood. Ichthyobodo necator, a common freshwater parasite, is a single-celled organism that can cause damage to fish gills and skin, leading to lethargy and loss of condition

 Leeches:

• Species: Piscicola geometra is the most frequent fish leech species in the UK. 
• Feeding: They attach to fish and suck their blood, potentially transmitting blood parasites and viruses. 
• Prevention: Reducing stress in fish populations, careful management of stock levels, and regular water quality monitoring can help prevent leech outbreaks. 
• Treatment: While some chemical treatments were previously used, they are now banned in the UK. Leeches can be removed with tweezers, and wounds should be treated with antiseptic to prevent secondary infections. 

also known as "Ich" or "Ick", is a common parasitic disease in freshwater fish caused by the protozoan parasite Ichthyophthirius multifiliis, appearing as small white spots on the skin and fins 

Cause: The disease is caused by the protozoan parasite Ichthyophthirius multifiliis. 

• Appearance: The parasite appears as small white spots, resembling grains of salt, on the fish's skin, fins, and gills. 
• Life Cycle: The parasite has a complex life cycle, including a free-swimming stage (theront) that infects fish, a stage where it feeds and grows on the fish (trophont), and a stage where it encysts and reproduces (tomont). 
• How it spreads: The parasite spreads rapidly from one fish to another, particularly when fish are stressed or crowded, or when water temperatures are changing rapidly. 
• Susceptibility: All species of freshwater fish are susceptible to the disease. 

Symptoms:

• White spots: The most obvious symptom is the presence of small, white spots. 

Other signs: Affected fish may also exhibit:

• Flashing (rubbing against objects) 
• Difficulty breathing 
• Lethargy 
• Loss of appetite 
• Excessive mucus production 

Treatment:

• Increased water temperature: Raising the aquarium temperature can help shorten the parasite's life cycle and speed up the treatment process. 
• Medications: Certain medications, such as those containing copper or malachite green, can be used to kill the parasite. 
• Quarantine: Isolate infected fish to prevent the spread of the disease. 
• Good water quality: Maintaining good water quality is crucial for preventing and treating the disease.