Koi Health (The Basics)

If a problem occurs in the pond you need to know what it is before treatment can be given. Medications, if given wrongly can be as lethal, or more so than the original issue.

At some time no matter how careful you are you will get sick fish. More often than not this can be avoided or reduced by vigilance. Spend as much time as you can watching your fish swim and feed - that's probably why you keep them anyway. But try to watch them sometimes without them knowing you're there, they will act more naturally. Watch out for that fish swimming on its own, does it normally do that? What about that one that hasn't eaten for 2 days could it be sick? Clamped fins are a giveaway of impending illness, and fish flashing can be a pointer to a problem, although this could be a water quality problem so, check Ammonia & Nitrite levels first.

Know your pond volume! Any "medicines" you use in your pond are in fact poisons meant to kill. At recommended doses the intention is to kill parasites etc. and do no harm to your fish but, if water volume is wrongly calculated at best the treatment will be ineffective, at worst fatal to your fish. Either way can be disastrous. A safer option is to maintain a Quarantine/Hospital tank. It is easier to maintain a controlled temperature and provide well aerated water. Other plus points are, it is cheaper to medicate 400 gallons than 4000, your pond filters will not be affected and in the case of any adverse reactions to the treatment the fish can be removed from the treatment water and returned to the pond environment.

With a Parasitic infestation although the parasite may itself not be a threat to the health of your fish the point of entry may be open to bacterial/fungal infection and should be cleaned and sealed with a proprietry medication.
Whitespot
Argulas (Fish Lice)
Signs :- apparent loss of appetite, flashing, bacterial/viral infection.
Reproduction :- dependant on temperature, eggs can hatch in spring if laid late summer.
Treatment :- In Pond Potassium Permanganate or Formaldehyde (not together).

Argulus will grow to 10mm across and use a pair of suckers to clamp on to the fish after which it injects a toxin to break down the tissue and feeds on the resulting soft flesh. Commonly, red marks can be seen and this leaves the site open to bacterial and viral infection which the fish louse can bring with it. The eggs of this parasite may be laid on the pond surface and are not susceptible to most treatments until hatched, which may be some months later depending on temperature. this condition is not treatable topically, pond treatment being the only solution.
If using Formaldehyde, salt should not be present in the pond, it will also kill plant life.
Potassium Permanganate loses it's effectiveness in algal laden water and is toxic in high Ph ponds.
Formaldehyde and Potassium Permanganate should NEVER be used together.
Formaldehyde, if used, should only be used in conjunction with Malachite Green.
Gill Flukes (Dactylogyrus)

Signs:- Initially "flashing" or scraping the body and gill area.
Reproduction:- Dactylogyrus are egg layers.
Treatment :- In Pondwith Formalin & Malachite Green mixture or Isolation Acriflavin or Chloramine T .

These parasites may infect the gills or skin of Koi, in fact most Koi carry them all the time like dogs or cats with Fleas and a small number of these "nuisances" do no harm. Fish may be seen to be mouthing air, trying to force water through their Gills to wash out the parasites or flicking at walls or bottom drain covers to dislodge them.
Just visible to the naked eye but a microscope is needed to see the "grappling hooks" they possess to hold on to and move around the fish causing irritation. Spring is usually the worst time for flukes as they become active before the Koi and, will get a good hold if the fish are weak or diseased sometimes numbering hundreds if not caught and treated.
Whitespot (Ichthyophthirius Multifilis)

Signs :- white spots like a sprinkling of salt, loss of appetite, excess mucous, possible body inflammation.
Reproduction :- varied, depending on temperature (approx. 4/5 days at 13deg c).
Treatment :- In Pond Malachite green/Formalin, once per week for 3 weeks.

A greatly magnified view of Ichthyophthirius Multifilis. This parasite can only be controlled in its free swimming stage, hence the 3 treatments. Because its reproduction cycle is temperature dependant one of the 3 treatments should eradicate this potential killer.
Argulus
Fish Lice
Dropsy

Signs :- protruding scales, bulging eyes.
Reproduction :- N/A
Treatment :- initially quarantine salt bath.

As can be seen from the pictures, left and right the two of the signs of dropsy are, bulging eyes (popeye or Exophthalmia) and raised scales (pinecone disease) both for obvious reasons.
Although not always fatal, unless caught early this is usually the case. Dropsy is not a disease itself but a symptom of another underlying cause, brought about by kidney failure and fluid retention. Possible causes for this can include :- bad water conditions, ulcers or damage, thereby letting water seep into the body, or sudden temperature changes, especially during the cooler months.
Affected fish should be quarantined straight away, taking care to rehouse them in a 1% salt solution (100 gm/10 ltr) at the same temperature as the pond. This temperature can then be raised (1deg C per day) depending on initial figure. Monitor water conditions for 10 days and top up salt if water changes are needed. During this period examine fish and pond to find out why this condition exists. Are more than one fish affected? If so this could be a bacterial infection - seek advice locally.
Dropsy
Skin Flukes (Gyrodactylus)

Signs :- As per Gill Flukes.
Reproduction :- Gyrodactylus give birth to live offspring.
Treatment :- As above.

These Parasites along with gill flukes may be found on various parts of the body and are not restricted to their named areas, they can also double their numbers every 24 hours.
Gill Flukes
Skin Flukes
Anchor Worm (Lernaea)

Signs:- May be seen with the naked eye protruding from the fish. Can be up to 20mm long. Inflammation due to secondary infection may be apparent.
Reproduction:- dependant on temperature, varying between 15/30 days
Treatment :- Seek Proffessional Medical Advice.

One of the most common crustacean parasites, the female Anchor Worm once attached to the gills mates with the male who leaves, ( his part in the process over). The female then migrates to the body, changing shape from the crustacean to the wormlike while living off the dissolved body tissue created by the digestive juices secreted into the host. This feeds the developing eggs contained within a pair of sacs which hatch and become free-swimming. When ready these juveniles return to the next host and, so the cycle continues. The female can produce many thousands of offspring during her lifetime.
Fish Leech (Piscicola Geometra)

Signs :- Generally not hard to miss, being up to 50mm long and banded, varying in colour from yellow to brown/red (depending on last feed). Fish may display lethargy due to anaemia.
Reproduction :- Anything up to 13 weeks

Trichodina

Signs :- Normally will show as a grey/white slime over the body, which the Koi produces to protect itself, this is self defeating as it encourages this protozoan parasite to reproduce at an accelerated rate. Can also infect the Gills and, if untreated quickly can be fatal.
Reproduction :- Ongoing
Treatment :- In Pond or Isolation Formalin & Malachite green or for stubborn cases Potassium Permanganate.