Encyclopedia of Parasitology

2016 Edition
| Editors: Heinz Mehlhorn

Ichthyophthirius multifiliis

  • Heinz Mehlhorn
Reference work entry
DOI: https://doi.org/10.1007/978-3-662-43978-4_1568


Greek: ichthys = Fisch, phtheiros = louse; Latin: multus = much, filia = daughter.


Species of  Ciliophora, phylum Alveolata.

Life Cycle

Figures 1, 2, 3, and 4
Ichthyophthirius multifiliis, Fig. 1

Life cycle of Ichthyophthirius multifiliis parasitizing many species of freshwater fish. 1 Swarmer penetrates the skin of a fish and becomes encysted (EN) by host tissues. 2 The encysted  swarmer grows to be a trophozoite, reaching a diameter of up to 1 mm; the skin then presents with a large grayish pustule at these places. 3 Upon rupture of the pustules, the  trophozoites, which have numerous contractile  vacuoles, are liberated and swim about feebly. Upon coming to rest on the bottom of the pond, the  trophozoite secretes a thick-walled gelatinous cyst wall about itself. 48 Within an hour of  encystation, the mother trophozoite starts reproduction by simple transverse division, this being repeated until up to 1,024 30–50 μm-long, pear-shaped swarmers (with a single contractile vacuole) are formed. 9 After rupture of the cyst, the liberated swarmer attaches to the skin of fish within 1 day (unattached ones die during the second day). CI cilia,CV contractile vacuole, CW cyst wall of cysts on the bottom of the pond, CWS cyst wall in skin, CY cytostome, EN encysting swarmer, LC long terminal cilium, MA macronucleus, MI micronucleus, OP opening rupture of CW, SW swarmer

Ichthyophthirius multifiliis, Fig. 2

Photo of two Black molly ornamental fish. One shows the typical white pustules of Ichthyophthirius multifiliis stages

Ichthyophthirius multifiliis, Fig. 3

Light micrograph of the skin of a fish with a trophozoite of Ichthyophthirius multifiliis in a feeding tunnel

Ichthyophthirius multifiliis, Fig. 4

Light micrograph of numerous Ichthyophthirius multifiliis stages in the fins of an ornamental fish



 White Dot Disease; name:  Ichthyophthiriasis: fish appear with white spots (Fig. 2). Due to the feeding of the trophozoites in the skin (Fig. 3), superinfections with bacteria occur and the fish often die due to lack of oxygen.


Protazol ® as medical bath.

Further Reading

  1. Mehlhorn B et al (1992) Health for ornamental fish. Springer, HeidelbergGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.Institut für Zoomorphologie, Zellbiologie und ParasitologieHeinrich-Heine-UniversitätDüsseldorfGermany