Fish Health Advice for Angling Clubs & Fisheries

Aeromonas Infection

Aeromonas bacteria cause ulcers, haemorrhaging and fin erosion, often linked to stress.

Columnaris Disease

Columnaris is a serious bacterial infection causing ulcers, fin rot and rapid fish losses in warm water.

Furunculosis

A serious bacterial disease causing boils, ulcers and internal bleeding.

Ammonia Burn

Chemical burns to gills and skin caused by poor water quality.

Barotrauma

Injury caused by rapid pressure change when deep-water fish are brought to the surface.

Gas Bubble Disease

Caused by excess dissolved gases leading to bubbles in tissue and fins.

Harmful Algal Bloom Exposure

Toxin exposure from red tides causing fish kills and lesions.

Saprolegnia

A cotton-wool-like fungal growth commonly seen on damaged skin or eggs.

Amyloodinium (Velvet Disease)

A deadly parasite causing rapid respiratory failure in marine fish.

Anguillicoloides crassus

Anguillicoloides crassus (we’ll call it A. crassus) is a tiny worm that lives inside the swim bladder of European eels. The swim bladder is like the eel’s built-in buoyancy aid — it helps them float, dive and swim properly. This parasite isn’t originally from Europe. It arrived in the 1980s when eels were moved around for fish farming, and has now spread across many rivers and lakes in the UK. Sadly, it’s now one of the biggest health threats our eels face.

Linked species: Eel

Anisakis spp.

Parasitic roundworms found in marine fish such as cod and whiting.

Argulus mongolianus

Argulus mongolianus is a newly discovered fish louse recently found in the UK. It attaches mainly to the gills, mouth, and head of fish, causing irritation, stress, and sometimes deaths. It has already been confirmed in carp, roach, and bream, and may infect all freshwater species. Because it is new and potentially harmful, reporting any suspicious lice or fish behaviour is very important.

Linked species: Carp ( F1 Hybrid ), Barbel, Bream ( Common ) & more

Blackspot

Blackspot is a common parasite that forms tiny black cysts on the skin and fins of freshwater fish. It looks alarming but is normally harmless and part of a natural cycle involving snails and birds. Only very heavy infections or small fish are affected. In most cases, blackspot is nothing to worry about.

Linked species: Carp ( F1 Hybrid ), Barbel, Bream ( Common ) & more

Caligus spp. (Sea Lice)

Marine sea lice affecting many saltwater fish species.

Chilodonella

Chilodonella is a fast-spreading parasite that attacks the skin and gills of freshwater fish. It can cause heavy mucus, grey patches, breathing problems, and even death if untreated. It thrives in poor water quality, overcrowded waters, and when fish are stressed. Good fishery management is the best way to prevent outbreaks.

Linked species: Carp ( F1 Hybrid ), Sturgeon ( Sterlet / Hybrid ), Sturgeon ( Sterlet / Hybrid ) & more

Cryptocaryon irritans (Marine White Spot)

Highly contagious marine parasite causing white cysts and respiratory distress.

Linked species: Poor Cod, Couchs Sea Bream, Lumpsucker & more

Dactylogyrus

A gill fluke that causes respiratory distress and can lead to mass fish deaths.

Ergasilus briani

Ergasilus briani is a tiny parasitic crustacean that sticks to a fish’s gills, a bit like a microscopic crab. It irritates the gills and makes it harder for fish to breathe. Heavy infections can stress the fish and slow them down.

Linked species: Barbel, Bleak, Bream ( Common ) & more

Ergasilus sieboldi

Ergasilus sieboldi, also known as the gill maggot, is a tiny parasite that attaches to the gills of freshwater fish. The adult females have long white egg sacs that trail behind them, making them easy to spot. They feed on the fish’s gill tissue, blood and mucus, which makes it harder for the fish to breathe and stay healthy. Heavy infections can cause fish to become tired, lose weight, grow slowly, or even die — especially in warm weather. This parasite can spread quickly through a fishery, so good fishery management and strong biosecurity are really important to keep fish safe.

Linked species: Bream ( Common ), Bream ( Silver ), Bream ( White ) & more

Gyrodactylus sprostonae

Gyrodactylus sprostonae is a newly recognised gill fluke causing major carp deaths in the UK. It reproduces extremely quickly, attaches to the gills, and can cause severe breathing problems and mortality. It mainly affects carp and crucians and is considered a serious emerging parasite. Good fishery management and quick reporting are essential.

Linked species: Carp ( F1 Hybrid ), Carp ( Common ), Carp ( Crucian ) & more

ichthyobodo necator

Ichthyobodo necator (Costia) is a rapidly spreading parasite that attacks a fish’s skin and gills. It causes lethargy, breathing problems, weight loss, and can be deadly—especially for young or stressed fish. It thrives in both cold and warm water, so good management and low-stress conditions are essential to prevent outbreaks.

Linked species: Carp ( F1 Hybrid ), Barbel, Bleak & more

Ichthyophthirius multifiliis (White Spot)

White Spot is a highly contagious parasite causing white cysts and rapid mortalities.

Lernaea (Anchor Worm)

A parasitic crustacean that embeds into the fish’s body, causing inflammation.

Piscicola geometra (Fish Leech)

Leeches attach externally and can transmit secondary infections.

Pseudoterranova (Cod Worm)

Large parasitic worms often found in cod and related species.

Schyzocotyle acheilognathi

Schyzocotyle acheilognathi, or the Asian tapeworm, is a long ribbon-like parasite that lives inside the intestines of carp and other freshwater fish. It attaches to the gut wall and steals the fish’s food, which can slow their growth, weaken them, and even block the intestine completely. Young fish are especially at risk, and heavy infections can cause serious health problems or death, so good fishery management and biosecurity are important to stop it spreading.

Linked species: Carp ( F1 Hybrid ), Bream ( Common ), Bream ( Silver ) & more

Sea Lice (Lepeophtheirus salmonis)

Parasitic copepods that damage skin and stress marine fish.

Linked species: Whitefish ( Powan / Gwyniad / Vendace / Schelly ), Brown Trout, Rainbow Trout & more

Trichodina

A disc-shaped parasite that irritates skin and gills, often linked to poor water quality.

Anguillid herpesvirus

Anguillid Herpesvirus (AngHV-1) is a warm-water virus that affects eels only. It attacks the gills and internal organs, making eels weak, tired, and unable to swim properly. Outbreaks usually happen in summer or when eels are stressed. Only a few cases have been found in UK rivers, but it may be more widespread, so reporting sick eels is very important.

Linked species: Eel

Carp Edema Virus

Carp Edema Virus (CEV) is a serious viral disease that affects carp, causing extreme tiredness (“sleepy carp”) and severe gill damage. It has caused sudden carp deaths in the UK and can appear in both warm and very cold temperatures. Only carp species are affected. Any signs of sleepy or dying carp should be reported immediately.

Linked species: Carp ( Common ), Carp ( Mirror )

Carp Pox

Carp pox is a common, mostly harmless virus that causes smooth white waxy patches on carp during winter and early spring. The lumps look worrying but rarely harm the fish and usually fade as the water warms up. Good water quality and low stress levels help keep the disease under control.

Linked species: Carp ( F1 Hybrid ), Carp ( Common ), Carp ( Crucian ) & more

EVEX

EVEX is a dangerous virus that affects only eels. It can cause bleeding, weakness, and sometimes death, and it can stop eels from reaching the Sargasso Sea to spawn. It has recently been found in wild UK eels, and early reporting of sick or dead eels is vital to help protect this endangered species.

Linked species: Eel

Infectious Haematopoietic Necrosis (IHN)

A notifiable viral disease primarily affecting salmonids in marine environments.

Linked species: Whitefish ( Powan / Gwyniad / Vendace / Schelly ), Brown Trout, Rainbow Trout & more

Infectious Pancreatic Necrosis (IPN)

A viral disease affecting young salmonids, causing high mortalities.

Koi Herpes Virus (KHV)

Koi Herpesvirus (KHV) is a serious virus that infects only carp and can cause large-scale deaths, especially in warm water. It leads to severe gill damage, breathing problems and “sleepy”, weak behaviour. The virus spreads easily on fish, nets, and water, and must be confirmed by laboratory testing. KHV is a Notifiable Disease and must be reported immediately.

Linked species: Carp ( Common ), Carp ( Mirror ), Carp ( Grass ) & more

Lymphocystis Disease

A common viral disease causing wart-like growths on fins and skin.

Spring Viraemia of Carp (SVC)

A notifiable viral disease affecting carp and related species.

Viral Haemorrhagic Septicaemia (VHS)

A serious notifiable viral disease affecting marine and freshwater fish.

Linked species: Poor Cod, Couchs Sea Bream, Lumpsucker & more