External parasites
Ergasilus: gill copepods
Ergasilus are small crustaceans associated mainly with the gills. Their attachment can damage local tissue.
An examination finding
They may be found attached using modified antennae. Breathing signs alone cannot identify this parasite; a gill examination needs appropriate expertise.
Prepare the history
Note the fish’s origin, recent introductions and whether signs affect one species or the whole pond. Send that information with any images the examiner requests.
Avoid home gill surgery
Do not cut gills or try to extract attached organisms with household tools. Get a fish-health assessment and a plan for the whole system.
Sources & further reading
Original WakeyKoi wording, informed by the references below. Linked clinical resources explain the evidence and their scope; they have not reviewed or endorsed this website.
Related guides
Educational guidance cannot diagnose an individual fish. Breathing distress, severe injury or unexplained losses need prompt professional assessment.