Care library / Health

Health guide, not a diagnosis · Serious if left

Gill & skin flukes

Also called gill flukes, body flukes, monogeneans, dactylogyrids (Dactylogyrus), gyrodactylids (Gyrodactylus)

Facts checked against sources on 16 Oct 2026. See sources

Signs

Rubbing on tank bottom/sides (flashing)
Fast breathing, swollen pale gills, gulping at surface in severe cases
Excess mucus
Clamped fins, lethargy, poor appetite
Scale loss or colour change where parasites feed

Cause

Monogenean flatworms. Gyrodactylids (live-bearing, mostly skin and fins) and dactylogyrids/ancyrocephalids (egg-laying, mostly gills). Dactylogyrids are mainly on cyprinids (goldfish, koi, barbs, danios, rasboras); outbreaks follow crowding, stress and poor water quality, and new fish bring them in.

What to do

Praziquantel is the treatment of choice for monogeneans in aquarium fish (whole tank). Eggs are not killed, so repeated or prolonged treatment is needed: UF/IFAS cites a 2–5 mg/L prolonged bath for 2–3 weeks, or 2.5 mg/L every other day to a total 10 mg/L, repeated every 1–4 weeks for 3 treatments. Re-examine fish 1–2 weeks after treatment. Reduce stressors (water quality, crowding, nutrition). Follow the product label for dosing.

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

Prevention

Quarantine new fish for at least four weeks, even if they look healthy, and check/treat during quarantine.

Medicines used for it

Always read the label first

DewormersParasite treatments

Seachem ParaGuardParasite treatments

Seachem CupramineParasite treatments

API General CureParasite treatments

Hikari PraziProDewormers

eSHa GdexDewormers

JBL Gyrodol / OodinolDewormers

Sera MycopurAntifungal

Sera OmnipurParasite treatments

Praziquantel (generic)Dewormers

Quarantine protocol kitQuarantine protocols

Sources

5 facts checked with sources

Other namesUF/IFAS EDIS FA033: Monogenean Parasites of Fish
CauseUF/IFAS EDIS FA033: Monogenean Parasites of Fish
SignsUF/IFAS EDIS FA033: Monogenean Parasites of Fish
What to docorrectedUF/IFAS EDIS FA033: Monogenean Parasites of Fish
PreventionUF/IFAS EDIS FA033: Monogenean Parasites of Fish

Species often affected

192 species

Cardinal tetraParacheirodon axelrodi

Moderate3 cm23–29 °C

Black neon tetraHyphessobrycon herbertaxelrodi

Easy3.2 cm20–28 °C

Black skirt tetraGymnocorymbus ternetzi

Easy7.5 cm20–26 °C

Serpae tetraMegalamphodus eques

Easy4 cm22–27 °C

X-ray tetraPristella maxillaris

Easy4.5 cm24–28 °C

Lemon tetraHyphessobrycon pulchripinnis

Easy3.8 cm22–28 °C

Congo tetraPhenacogrammus interruptus

Moderate8 cm23–28 °C

Glowlight tetraHemigrammus erythrozonus

Easy4 cm24–28 °C

Rummy-nose tetraPetitella rhodostoma

Moderate5 cm24–27 °C

Ember tetraHyphessobrycon amandae

Easy2 cm24–28 °C

Bloodfin tetraAphyocharax anisitsi

Easy5.5 cm18–28 °C

Emperor tetraNematobrycon palmeri

Easy4.2 cm23–27 °C

Penguin tetraThayeria boehlkei

Easy6 cm22–28 °C

Head and tail light tetraHolopristis ocellifera

Easy4.5 cm24–28 °C

Bleeding heart tetraMegalamphodus erythrostigma

Moderate6.1 cm22–28 °C

Tiger barbPuntigrus tetrazona

Easy7 cm20–26 °C

Cherry barbRohanella titteya

Easy5 cm23–27 °C

Rosy barbPethia conchonius

Easy10 cm16–24 °C

Odessa barbPethia padamya

Easy4.6 cm16–25 °C

Gold barbBarbodes semifasciolatus

Easy7 cm18–24 °C

Denison barbDawkinsia denisonii

Moderate15 cm18–25 °C

Black ruby barbPethia nigrofasciata

Easy6 cm20–27 °C

Tinfoil barbBarbonymus schwanefeldii

Hard35 cm20–28 °C

White cloud mountain minnowTanichthys albonubes

Easy4 cm14–22 °C

AngelfishPterophyllum scalare

Easy15 cm24–30 °C

German blue ramMikrogeophagus ramirezi

Moderate4.2 cm27–30 °C

Bolivian ramMikrogeophagus altispinosus

Moderate8 cm24–28 °C

Cockatoo dwarf cichlidApistogramma cacatuoides

Moderate7.5 cm24–28 °C

KribensisPelvicachromis pulcher

Easy10 cm24–27 °C

Convict cichlidAmatitlania nigrofasciata

Moderate10 cm24–28 °C

Jack DempseyRocio octofasciata

Moderate25 cm22–28 °C

Firemouth cichlidThorichthys meeki

Moderate17 cm24–28 °C

SeverumHeros efasciatus

Moderate20 cm22–29 °C

Green terrorAndinoacara rivulatus

Moderate20 cm20–24 °C

Electric blue acaraAndinoacara pulcher

Easy15 cm22–28 °C

Comet goldfishCarassius auratus

Easy30 cm10–24 °C

KoiCyprinus rubrofuscus

Moderate70 cm4–25 °C

MedakaOryzias latipes

Easy4 cm16–22 °C

Agassiz's dwarf cichlidApistogramma agassizii

Moderate7.5 cm23–28 °C

Yellow dwarf cichlidApistogramma borellii

Easy6.5 cm20–26 °C

Three-striped dwarf cichlidApistogramma trifasciata

Moderate5.5 cm20–25 °C

MacMaster's dwarf cichlidApistogramma macmasteri

Moderate5.5 cm24–28 °C

Hongslo's dwarf cichlidApistogramma hongsloi

Hard6 cm24–28 °C

Banded dwarf cichlidApistogramma bitaeniata

Moderate7.5 cm24–28 °C

Panda dwarf cichlidApistogramma nijsseni

Hard3.9 cm24–28 °C

Viejita dwarf cichlidApistogramma viejita

Moderate23–28 °C

Panduro dwarf cichlidApistogramma panduro

Moderate7 cm24–28 °C

Inka dwarf cichlidApistogramma baenschi

Moderate5.5 cm20–26 °C

Steindachner's dwarf cichlidApistogramma steindachneri

Moderate8 cm20–25 °C

Diplotaenia dwarf cichlidApistogramma diplotaenia

Moderate3 cm24–28 °C

Juruá dwarf cichlidApistogramma juruensis

Moderate2.4 cm24–28 °C

Pucallpa dwarf cichlidApistogrammoides pucallpaensis

Moderate4 cm22–27 °C

Checkerboard cichlidDicrossus filamentosus

Hard3.8 cm27–30 °C

Spotted dwarf cichlidCrenicara punctulata

Easy12 cm23–27 °C

Golden dwarf cichlidNannacara anomala

Easy7.6 cm22–26 °C

Sheepshead acaraLaetacara curviceps

Easy8 cm22–28 °C

Red-breasted acaraLaetacara dorsigera

Easy8 cm22–28 °C

Sunset dwarf cichlidTaeniacara candidi

Hard5 cm27–30 °C

Cupid cichlidBiotodoma cupido

Moderate12 cm24–28 °C

Altifrons eartheaterGeophagus altifrons

Moderate25 cm26–30 °C