you probably have a few things going on. Since the koi lived long enough to get a nasty infection, we can pretty well rule out parasites such as costia and ich since those can kill pretty quickly. I suspect a parasite was still responsible, possibly flukes. Flukes are irritating and cause a break in the skin. The bite gets infected, causing an ulcer. The fish is now sick, and a fungus called saprolegnia starts growing on the ulcer. Saprolegnia releases toxins into the fish making him even sicker. SAP alone can be deadly. I realize it is too late for this one, but in the future here's how I would treat that fish. Catch the fish and sedate. Gently scrub the wound with a q-tip and betadine. Remove all traces of fungus or it will grow back. Be sure to keep betadine out of the gills!! Treat the sore with a paste made of potassium permanganate (dangerous stuff....handle with care), or malachite green. Seal the wound with denture powder. With an ifection as bad as that one, I would also treat with an injectible antibiotic such as amikacin. The fish needs to be returned to a clean QT and the temperature needs to be slowly brought up from the pond temp to around 70°. A koi cannot heal in cold water. Further investigate the possibility of flukes on other fish. Symptons include flashing, jumping, excessive slime coat.

Hi Ademink: I raise about 1/2 tons of salmon and trouts and used to raise koi as well. What you have described is sometimes commun when females can not release their eggs for some reason (not enough oxygen, hardness too low, water temp too high, chlorine/chloramine or polutents in the water... During the re-absorption process, it may take a few weeks, it is important to oxygenate the water. My preference is to oxygenate by moving water with a pump, air stone may be more damaging. Oxygen bubbles from an air stone may get trapped in the gills preventing dissolved oxygen to cyrculate properly. Salting does not solve all the problem...! As a matter of fact may creat others... Do check your harness and alkalinity as you should anyways. Proper hardness will help eggs in their hardening process, render any polutents especially metals significantly less toxic to fishs, prevent pH fluctuation and along with oxygen helps the bacteria to process waste. Have you noticed any eggs (white looking stuff) in the plants?

Ccoombs is an expert when it comes to Koi and she is probably correct in her diagnosis but one other option to consider would be Swim Bladder Disease since it is fairly common. It would give the same bulge on just one side but usually the fish would swim with more difficulty, listing to one side or staying either on the surface or on the bottom. The difference is this condition can be treated. That is why I mention it. A partial list of suggestions that could help: "Feed your fish a couple of peas. That's right, peas. Just get some frozen peas, thaw them, and feed them to your fish. A professor of fish medicine at N.C. State College of Veterinary Medicine has done this in several cases with very good results. He thinks that the peas somehow encourage destruction of the impaction. No hard scientific data yet, but it's worth a try. Fast your fish for a couple of days. Withhold all food for three or four days, and sometimes this alone will break up the impaction and return things to normal. Most fish can go a week to ten days without food and be just fine. Periodic aspiration of the swim bladder works very well. Basically, you stick a needle in the swim bladder and suck out some of the air. Not something to be entered into lightly, but does work well. This is not a cure, but a successful treatment. The head veterinarian at the Baltimore Aquarium prefers this method. Partial pneumocystectomy. This is another word for surgical removal of part of the swim bladder. I mention this less as a practical option but more just to let people know that there are vets out there doing X-rays, surgery, general anesthesia, even cancer chemotherapy." I've never had a fish with a tumor but I have had one with a swim bladder problem. It resolved itself with the peas and gentle massage at the edge and lower back of the swelling. this might not help your fish at all if it is a tumor but it couldn't hurt. Some people prefer to cook the peas for a few seconds and then pop out the inside of each pea. Throw away the skin of the peas. It is tedious but my fish love them. Here is a link that might be useful: never stick a swollen swim bladder with a pin! leave that to a vet.

I have been building, rebuilding, digging, re-digging, in short, building a pond for koi. It has evolved to two waterfalls, the large one in a spiral half circle stair-step down, and the small one,is a little pool dropping down over a ledge of flat rocks. The main body is 16' x 8 1/2' and 4 to 41/2' deep, with the rock waterfall on this end. This runs into a channel 3' x 41/2' with a bridge over it. This runs into the little pool that is 41/2' x 5 1/2' and 31/2 ' deep. The large spiral waterfall drops into it. I live in Montana, and I have wintered several winters with my Koi, of course keeping it open, and an aerator keeping the water moving. This past spring I love some of my big Koi, due to a fungus of some sort. I have large and small koi including 3 that were born and survived in the pond with the others. I had babies this year but don't know if any have lived. The big ones had a feast. I have been pretty much trial and error, and lack any one around here to ask questions of, so I am glad to find this listing. What I found out this summer was that Koi like oranges. I toss a half a slice into the pond and wait for the feeding frenzy. They will climb over each other to get to the orange. They eat the pulp and leave the rhine.(you get to fish that out). When I read about this I wasn't to sure, but after the first couple of times, they are right there, and it's good for them. I have about 11 Koi (different sizes) ranging from the big white one to the year and a half babies, about 7 inches or so. I have 4 butterfly Koi, about 9" or so. There is more then one female in the pond, and several males, I'm not to sure which is which, except the white one is female.She is about 20 some inches, and a couple of the others are also about that size. I know there were babies, because one made it to the top of the big waterfall, in an unconventional way. (Though the pump,uv light and about 8' of hose.) He ended up back down into the pond. I hope he didn't get eaten. I have no place for babies other then the pond, so some may survive, and I'll see them next year. Anyway, I have a blog with pictures of how it started and grew, and what it is now, if anyone would like to see it. I never know what is going to happen next out there, so the next problem that crops up I will ask for help. Tonight the big toad was out, and I know there have been babies, as I've seen one tiny one hopping around. This has been a challenge, but I do love my Koi.