"what's on my fish" ?

Trichodina (Nobilis chen/Reticulata),

Trichodina is a genus of ciliated protozoans that primarily parasitize fish and occasionally amphibians.

Ciliates are creatures that possess cilia, which are tiny hair-like protuberances that enable the creatures to “swim” about fairly efficiently. In parasites, this is key for being able to travel from host to host.

Trichodina infestations are typically rare, as they prefer water bodies with stagnant, unhealthy waters over clean water. Goldfish are most often affected by  Trichodina, but koi are susceptible as well.

If you know or suspect that your pond has Trichodina, you must confirm and treat it as quickly as possible to prevent your fish from becoming ill or, in extreme cases, dying.

What Is Trichodina?

Trichodina is found in the family Trichodinidae. All members of this family are obligate ectoparasites, meaning that they only live outside of the host’s body and must have access to a host to fully complete their life cycle.

There are over 150 species in the Trichodina genus, with the majority of them not being true parasites to their hosts. Rather, most of them simply use fish as an anchor point to attach to while they feed on bacteria and other microscopic organic material that floats by.

However, even these can cause issues in fish as they may damage the sensitive slime coating and epidermal skin layer, resulting in an increased risk of the fish developing infections and secondary illnesses.

The collective name for diseases caused by trichonids is trichodinosis. A handful of species may feed on dead tissues and settled organic material that is found on the surface of the fish’s skin, but otherwise do not directly parasitize the fish.

It is not Trichodina that kills fish; rather, it’s the secondary ailments that host fish become much more susceptible to upon colonization.

Where Does Trichodia Come From?

Most often, Trichodina establishes in an ecosystem due to poor water quality and overcrowding.

If found in a relatively healthy pond, they were likely introduced via a new fish that was raised in less than ideal conditions (such as an overstocked fish farm) and then not properly quarantined by the new owner before being placed in the pond with other fish.

They can also pioneer via new plants that were kept in poor conditions. For this reason, any new plants should be thoroughly rinsed off and checked over, if possible, with a microscope to ensure that parasites are not present on their roots.

If potted in soil or substrate upon purchase, remove and dispose of the soil/substrate just in case Trichodina are present, and again thoroughly rinse off the plant’s roots before planting in or near your pond.

They are most often found on the gills and fins of fish but can exist anywhere on the skin. Some species prefer the urogenital ducts, where plenty of bacteria can be found for them to feed on.

How to Identify Trichodina in Ponds trichonids are quite small, approximately 18 to 100 micrometres in diameter depending on the species, with a spherical shape and a basal (located on the underside of the body) disc that enables them to attach to hosts.

These basal discs have dozens of denticles, which are incredibly small, sharp, tooth-like structures that enable secure affixion to their host organism, which could be a fish, frog, salamander, or other


such as aquatic or semi-aquatic organism. Due to their size, trichonids are most easy to identify under a microscope by taking water and/or small tissue samples.

Trichodina species have a pretty simple life cycle, relying on only one host and only needing to find a new one if they somehow become detached from the initial one.

Trichonids attach to a host, reaching maturity within a span of only a few days. Once maturity is reached, they don’t need a mate to reproduce – rather, because they are single-celled organisms, reproduction is done via binary fission, literally splitting themselves in half.

The daughter cell either attaches to the current host or utilizes its cilia to swim to a new one. They must find a host within 24 hours or most trichonids will die. Once a host is secured, the process repeats itself.

What Are Symptoms of Trchodina?

Flashing Koi

infected with Trichodina or any other parasite may display erratic behaviours such as flashing, jumping about, and rubbing against rocks and walls to try to rid themselves of the uncomfortable parasite.

Skin Sloughing

The longer that Trichodina is present, the more damage they are likely to do to the skin as they sort of spin in place continuously while attached to the fish. Over time, skin becomes damaged enough that it sloughs off, which can then be ingested by the trichonids.

Excess Mucus

Koi that have trichonids attached to them may produce excess epidermal mucous to try to fend off the parasite. This can cause fish to appear to have a whitish-grey, sometimes grey-blue, muted hue.

Skin Discolouration

The skin around trichoid attachment sites may be pink or red, depending on the severity of irritation and whether or not a secondary infection is present.

Skin Lesions

Lesions and ulcers can develop in more serious cases as parasite attachment sites become more agitated and are invaded by bacteria, fungi, and any viruses present. This is of particular concern if fish are rubbing against things and thus scrape their sides raw, inviting in even more bacteria and secondary infections.

Damaged Gills

When trichonids attach to gills, the gills can become damaged and somewhat ratty looking over time as skin dies and falls off. They can also become a pinkish or deep red colour. Damaged gills can result in impaired swimming over time.

White Patches

As skin dies around Trichodina attachment sites, your fish will display obvious, small white splotches.