"what's on my fish" ?

CHILODONELLA (Chilodonella uncinata)

Chilodonella is a single-celled ciliateendo parasite. Endoparasites are those that live a somewhat symbiotic

Relationship with their host:
Chilodonella in particular use fish simply as an anchor point so that they can more easily feed on passing bacteria and microbes.

Regardless of not specifically feeding on their fish hosts, Chilodonella should still be treated as soon as they have been identified in your pond or you notice symptoms in your fish.

While only a few Chilodonella doesn’t typically cause harm if allowed to remain they open your fish up to a host of harmful secondary diseases and infections.

What is Chilodonella?

Chilodonella belongs to the family Chilodonellidae, within which they are the only genus. Most species utilize fish as host vessels, but one particular species is being used as a natural biocontrol approach to disease-carrying mosquito populations.

Chilodonella uncinata seem to only prey on mosquito larvae, helpfully causing massive mosquito mortality in developing countries with troublesome insect populations, such as India. These tiny parasites are most likely to be found in, on, or near the gills of fish, particularly in Chilodonella’s juvenile stages.

As they become stronger from feeding, though, they may move about on fish and attach anywhere on the skin. While Chilodonella is not themselves overly harmful, they do open fish up to secondary illnesses and diseases.

Where Does Chilodonella Come From?

Most often, they are transferred to ponds via infected fish that were not properly taken care of (as is usually the case if they’ve come from an overstocked fish farm), and not quarantined before being introduced to a new pond.

How to Identify Chilodonella in Ponds

At all life stages, Chilodonella is microscopic, making them almost impossible to identify with certainty unless a microscope is used. Multiple water samples should be looked at, as well as skin scrapings from fish at suspected attachment sites (scraped gently to not stress or further harm the fish).

They are described as being pear or pear-shaped, with many small, hair-like cilia on their ventral side (the side that is longer).

Their size is typically 30 to 70 micrometres (µm) long and 30 to 50 µm wide. For comparison, the average human hair width is between 100 µm.

Life Cycle of Chilodonella?

Mature Chilodonella reproduce asexually via meiosis to create daughter cells that develop into adult Chilodonella within only a few days. Occasionally, when resources are scarce and one does not possess the energy for meiosis, they may reproduce via joining together through a process called conjugation.

Two Chilodonella join together, creating a sort of bridge through which they exchange resources and genetic information, to form a zygotic nucleus that is capable of then undergoing meiosis.

Their life cycle is relatively short, reaching reproductive maturity in 72 hours or less. Daughter cells can immediately either attach to the existing host fish or use their cilia to swim to a new one. Most often, they attach on or near gills, though they can be found anywhere on the skin as well.

Their ventral side is concave, enabling them to essentially vacuum-seal themselves to their hosts without burrowing into the skin. If Chilodonella cannot find a host within 24 hours, they are likely to die.

With a host, however, Chilodonella can survive for many months, capable of going dormant if temperatures fall above or below their ideal range.

Cooler water temperatures of 40 to 50° F (5 to 10° C) suit these parasites best, making them of particular concern in the spring when temperatures are both cooler and fish immune systems tend to be weaker due to coming out of winter torpor.