External Parasites

Single Cell Parasites- One of the most common and fatal diseases of koi is Ichthyopthiurius multifilis, or “Ich”. It is a ciliated protozoan that has a complex life cycle. It has a growth stage in the pond, and a mature stage in the skin and gills of koi. It is not known if there is more than one variety of Ich, so any the best defense. Microscopic examination of skin and gill biopsies is needed to see this parasite. The adults are easy to recognize by the very large

Other common single cell parasites include: 
Costia (Icthyobodo), Oodinium, Chilodonella, and Trichodina. 
Except for Ich and Oodinium, which have an encysted stage in the pond, these parasites are transmitted directly from infested fish to clean fish. None require an intermediate host (another animal Potassium permanganate or formalin can also be effective. Parasites are eliminated from the return water after passing through ozone (caution is advised with ozone since it can be very toxic to fish if it finds its way into the pond) or an ultraviolet light of sufficient strength and contact time, but are not eliminated from the pond or on the fish. The fish’s own defense mechanisms, including the slime coat, intact skin and a fully functional immune system, must remove them or control them, but reducing the load in the water by treatment with ultraviolet light, formalin or salt will be beneficial in reducing the parasite load on the fish.  
Multi-cellular Parasites- There are many species of multi-cellular parasites. In general, complex parasites require specific treatments and are generally more resistant to environmental changes. These gill or skin flukes, leeches, fish mites, and crustaceans (anchor worm and fish lice). Skin and gill flukes belong to the Trematode group. They are obligate parasites. All of the species of Weekly skin scrapes and gill biopsies are recommended to assess the effectiveness of treatment, and therefore the interval between treatments. Droncit® is crustacean parasites. Salt has been used successfully to treat Dimilin® and Program® are insect growth regulators. This class of medicine interferes with the ability of some arthropods (crustaceans and insects) to form new exoskeleton by interfering

The life cycle is temperature dependent, so colder water will need to be treated for a longer period of time, or repeated more times. Most ponds will need to be treated weekly for 4-6 treatments to kill adults, or once, if followed by a treatment that kills the larval stages. It is recommended that each user obtain

In general, external parasites cause flashing, respiratory distress, overhydration, chronic mortalities, clamped fins, excess mucus, and decreased appetite and are often associated with a secondary bacterial However, every attempt to determine the cause should be done prior to adding the salt, so that a complete and accurate assessment can be made which will direct the next course of action.

THE SEVENS STEPS OF ICH.

1. Koi infested with Ichtyophthirius *trophonts*

2. Trophonts *trophozoites* embeded feeding stage: spherical cell completely covered in cilia with aU-shaped mactonucleus. Grow  up to 1 mm in the epidermis( outer layer of skin) of fish until mature. Feeds by absorbing tissue fluid.

3. Trophants leave host when mature and attaches to plants, gravel or other substrates. There it forms a *cystic* capsule (tomont stage) and begins mitotic cell division.

4. Mitotic division continues for up to 10 times producing hundreds and up to a thousand new *protozoa*

5. The tomont's cystic ruptures and the free-swimming ciliated tomites *theronts* are released. This is the *ONLY STAGE OF ICHTHYOPHTHIRIUS THAT IS SUSCEPTIBLE TO TREATMENTS.
24-48 hours.

7. Tomites penetrates and embeds in the epidermis of the skin or gill epithelium, where it matures as a trophont.

The cycle repeats and the length of tome depends on water temperature.

Trophont time to maturity

At 70 deg F is 5 days
At 80 deg F is 3 days.

Tomont division time
At 77-80  deg F is 10-12 hours
At 64-68 deg F is 20-24 hours

Tomites will not survive in water warmer than 84-86 deg F also ultraviolet light will kill the tomites.

Standard dosages if formalin/malachite solutions will kill the free swimming tomite stage, but the trophont and tomont stages are resistant to treatments. This is why treatments must continue long enough for *all* the trophonts to develop into tomonts and *then* into new tomites where they are susceptible to treatments