Eel junior fishing guide

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.

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.

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.

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.

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.

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.