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Koi Diseases or Disorders of the Gill

Koi Gills The outer rim or edge of the gill seem to be pale, frayed or white.

If you look at the gills of your koi and they are nice and steak red but the outer "crescent moon" edge of the gill is pale or white, then something has "burned" the gills. Lots of retailers perform potassium dips on the fish before shipping. Formalin dips, a crashed pH, Ammonia burns and nitrite accumulations and more can cause caustic burns to the gill. A white edge to the gills is NOT a diagnosis of bacterial gill disease. Usually these fish DON'T need medications inasmuch as they need water testing, cool clear water, and time to heal from the burn.

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Koi Gills There are scalloped 'blow outs'' in the gill arches.

When you lift the gill cover and there are actual holes in the gill tissue, you have classic bacterial gill disease. I ALWAYS start these cases with a microscopic biopsy to rule out parasites, and then inject all fish with medications. If this is not feasible, feeding MediKoi can be helpful and effective in the fish that will still eat. Treating the koi in a holding tank with Ulcer Aid Rx can be very helpful as this medicine is safe and powerfully antibacterial. Never use Ulcer Aid Rx in the main tank.

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Koi Gills There are strands of white amongst the normal gill filaments.

This is a fairly treatable, but insidious (wide spread throughout the pond) form of bacterial gill disease, and is usually associated with parasitism. Almost every time I have seen THIS form of bacterial gill disease, it's been caused by Flukes or some other gill parasite. If the fish are not dying off rapidly, you can forget about Costia for the time being and use a combination of Salt and Aqua Prazi for good results if you can't do a scope biopsy.

Update: because of the over use or salt, there are now many “salt resistant” parasites. If the parasites do not respond to salt, the recommended treatment would be TERMINATE which is made to treat “salt resistant” parasites.
  • Fish dying in dribbles and drabs.

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Koi Gills The entire gill is pale, hamburgerlike and greenish.

When you see gills like this, the important thing is to examine the gills of any other fish in the tank which is important. The reason is that this is the worst presentation of bacterial gill disease. Like most forms of gill disease, it is highly morbid (widespread in the pond) and many normal-acting fish will have gill lesions. To put the reigns on this one, you need injections for all valuable fish, or Ulcer Aid Rx and medicated koi food.

  • Usually Springtime, usually warmer water. Lots of fish dying.

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Koi Gills Gills are just pale.

Just-pale gills are essentially normal insofar as they aren't missing chunks of tissue as above. The edge of the gill is usually homogenous with the rest of the gill, but the whole gill is simply pale. This is ALMOST ALWAYS the way gills look when there is poor water quality with concurrent gill infestation with parasites. I rarely see pale gills without a solid, dense population of gill flukes. The reason the gills are pale is because the gills are bleeding through thousands of tiny microvascular lesions created by the parasites. For this, expect to lose more fish, but bring it under control with salt and Medicated koi food. The real "edge" goes to those who can kick off the whole regimen with an injection of antibiotics for the affected fish.

Update: Ulcer Aid Rx has really changed everything as it replaces injections for those whom are afraid to give them.

Update: because of the over use or salt, there are now many “salt resistant” parasites. If the parasites do not respond to salt, the recommended treatment would be TERMINATE which is made to treat “salt resistant” parasites. 

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Koi GillsGill covers (opercula) are swollen, almost open
When you see a fish with swollen gill covers, you can almost assume that Flukes are chronically present in the case. Examine the gills and see what they look like. Compare the condition of the gills to the cases above. If they gills are crimson and healthy, then it would be an odd case. A microscope biopsy would also shed light on the case. If you discover that Flukes are the actual trouble, consider their clearance using Aqua Prazi

Hole in the gill cover
It would be unlikely that this would be anything other than tuberculosis. The prognosis is not very good. Injections or Ulcer Aid Rx plus, impeccable water quality would be recommended. The fish can live with a hole in it's gill cover if you can save it from the infection.

Action Items
1stMake sure your water tests for Ammonia, Nitrite and Nitrate are good. Don't settle for "normal" but get numbers. Keep records.
2nd Make sure your pH is above seven. Again, "normal" is not a bona fide pH level.
3rd Change 75% of the pond water without causing more than a 15 degree drop in temperature. You should be aware that in cooler water, fish will respire more easily.
4th Clean the pond and filter. For all forms of gill disease, the pond needs to be fabulously clean. Flow rates and filtration should be optimized.
5th Inject all fish with Baytril or Azactam. Instructions should be provided with these medications from the provider, or treat with Ulcer Aid Rx 
6th All fish with bacterial gill disease should be treated to medicated koi food. Even if they were injected, this is a good idea to perhaps avoid the necessity to overhandle for more injections.

7th If parasites have not been ruled out, concurrent treatment with SALT and Aqua Prazi is recommended. This is a dynamite, safe combination which only overlooks Costia.

Update: Because of the over use or salt, there are now many “salt resistant” parasites. The NEW recommended treatment would be TERMINATE which is made to treat “salt resistant” parasites including costia.


Needed or Recommended Items
+ Water in the low seventies improves oxygen transfer.
+ Water test kits are necessary.
+ Will need dechlorinator in most instances for major water changes.

+ Antibiotics, either by injection or milled into the food are the mainstay of treatment.

Ulcer Aid Rx has really changed everything as it replaces injections for those whom are afraid to give them
+ Do not go crazy with waterborne remedies and additives. Almost all of these are irritating to the already-damaged gill tissue and decrease oxygen transfer. Low level salting, a mere one pound per hundred gallons is a good idea.
+ Most gill disease outbreaks resolve after the continued loss of more fish. A certain percentage are "just too far gone." Bacterial Gill Disease is a difficult disease to quickly bring under control. People underestimate the importance of cool clean water in it's treatment.