Trichodina

Trichodina is a genus of ciliate protozoa in the family Trichodinidae, commonly classified with the Peritrichia. These organisms are ectoparasites or epibionts that colonize the external surfaces of aquatic animals, especially the gills and skin of freshwater and brackish-water fish. They are widespread in natural waters and are common in aquaculture and aquarium systems, where heavy infestations can occur under stressful conditions.

Morphology: Trichodina species are small, usually disc- or umbrella-shaped ciliates, roughly 20–60 micrometers in diameter. They possess a ventral adhesive disc that enables attachment to host tissues. A diagnostic feature is a ring or hood of cilia around the anterior body, forming an adoral zone used in feeding. The cytoplasm contains typical ciliates structures, including macronucleus and micronucleus, and the pellicle is relatively thin.

Life cycle and transmission: They spend part of their life attached to the host as trophonts, feeding on bacteria and organic material on the surface. Reproduction is primarily by asexual binary fission, either while attached or after detachment. Free-swimming progeny can disperse to colonize new sites or hosts through water movement or contact.

Pathogenicity and management: Heavy infestations irritate host tissues, increase mucus production, and can contribute to stress and secondary infections. Management includes good water quality, reduced stocking density, and the use of approved antiparasitic treatments under veterinary or aquaculture guidelines.

Ecology and significance: Trichodina is a common component of protozoan communities in aquatic systems and serves as a model for studying host-parasite interactions in fish.