Caring For Pondfish: Gill Flukes, Skin Flukes of Goldfish & Koi

The descriptions of the common fish diseases have been deliberately kept simple to assist the understanding of the basic problems that may be encountered. This is a fascinating aspect of pond keeping and massive amounts of resource for further study can be found across the Internet.

The key to disease control is observing goldfish or koi behavior. Any lasting changes to normal behavior should be investigated because this is the first indication that something in the pond might be wrong.

A correct diagnosis normally needs more in-depth examination often using a microscope.

Gill and Skin Flukes On Pond Fish ...

• Freshwater flukes are microscopic in size and are reported as Gill Fluke, and the second class is the Skin fluke. Gill flukes lay eggs and the rate of egg laying is a function of pond temperature ... low temperature slow rate and vice versa. The incubation within the egg is also temperature dependent.

• Flukes attach themselves to hosts in the gill region. Flukes come equipped with hooks at one end of their body. The use these hooks to attach themselves to the goldfish or koi. They also use them as paddles to be able to move around in a jerky fashion. Flukes are small so you'll only really see the hoos under microscopic conditions.

• Skin flukes produce live young which immediately infect the host. They reproduce rapidy.

• Flukes feed on blood within the fish's gill or skin. Skin flukes are happy to live in the gills and gill flukes also live on the skin.

• Flukes survive in 0.3% salt solutions. The main cause of fish deaths seems to be related to secondary bacterial infection from Aeromonas and Pseudomonas types.

• The oxidation and disinfection characteristics of Potassium Permanganate are able to control flukes at the level of 0.2%. Some recommend the use of formalin but this has a severe negative effect upon bio filter bacteria and should be avoided if possible.

Dactylogyrus (Gill Fluke) ... advice from Ben Helm

One of the many parasites of koi that will cause them to flick and scratch through irritation. The gills are very appetising for parasites as they offer a constant source of food that is very accessible, with the gills having such a thin penetrable membrane separating the nutritious blood from water. However, there is also a strong stream of water pumped across the gills which means that to hang on, gill flukes need a serious pair of hooks to hold on - hence the irritation to the fish.

A case of Dactylogyrus can be difficult to diagnose in koi as they are barely visible to the naked eye and are tucked away out of sight in the opercular chamber. It is not possible to take a live sample as there is a real risk of damaging the delicate gill tissue. However, it is rare for a gill fluke problem to be an isolated infestation and usually occurs with an increase in other ectoparasites such as Chilodinella, Trichodina and Gyrodactylus which can be easily diagnosed with a skin scrape. Thankfully, the treatment for the skin fluke will also be effective against the gill fluke.

Treatment can be effective using a series of prolonged salt baths with an investigation into the cause of the initial problem. Another extremely effective yet controversial form of treatment is using an organophosphate compound containing trichlorphon. This product although effective is not licensed for use in aquaculture