Health guide, not a diagnosis · Serious if left

Fish lice

Also called argulus, fish louse

Signs

A flat, see-through round parasite moving on the skin
Rubbing and red spots

Cause

Argulus, a crustacean parasite, mostly on goldfish and koi.

What to do

Remove lice with tweezers and treat the whole system with an anti-parasite medicine; repeat to catch new hatchlings.

If a fish is badly ill, talk to an aquatic vet.

Prevention

Quarantine; don’t add wild pond water or plants.

Medicines used for it

Always read the label first

DewormersParasite treatments

Species often affected

20 species

White cloud mountain minnowTanichthys albonubes

Easy4 cm14–22 °C

Comet goldfishCarassius auratus

Easy30 cm10–24 °C

KoiCyprinus rubrofuscus

Moderate70 cm4–25 °C

MedakaOryzias latipes

Easy4 cm16–22 °C

ShubunkinCarassius auratus

Easy30 cm4–26 °C

Golden orfeLeuciscus idus

Moderate50 cm4–22 °C

Rosy red minnowPimephales promelas

Easy10 cm4–26 °C

European bitterlingRhodeus amarus

Moderate8 cm5–22 °C

Pumpkinseed sunfishLepomis gibbosus

Moderate20 cm4–25 °C

Bluegill sunfishLepomis macrochirus

Moderate25 cm4–26 °C

Blue-spotted sunfishEnneacanthus gloriosus

Moderate9 cm8–24 °C

Banded sunfishEnneacanthus obesus

Moderate9 cm8–24 °C

Everglades pygmy sunfishElassoma evergladei

Moderate3 cm10–26 °C

Three-spined sticklebackGasterosteus aculeatus

Moderate8 cm4–22 °C

Nine-spined sticklebackPungitius pungitius

Moderate6 cm4–20 °C

Sterlet sturgeonAcipenser ruthenus

Hard100 cm4–20 °C

TenchTinca tinca

Easy50 cm4–25 °C

Golden ruddScardinius erythrophthalmus

Easy40 cm4–25 °C

SunbleakLeucaspius delineatus

Easy9 cm4–22 °C

Vietnamese white cloudTanichthys micagemmae

Easy4 cm16–24 °C