I just saw the weirdest thing. One of my two remaining "healthy" koi did something very unhealthy. He died. I was out tending to my system, and I noticed him floating belly up, being carried by the current of the water (he's tiny........only about 6" in size). So I scooped him into my hands to look him over. His side fins were completely stuck straight out, horizontally. His mouth was CLOSED. I took him out of the water to see if I noticed anything out of the ordinary. Now, I'm no fish doctor, but nothing screamed out to me as showing signs of illness. I do see little black spots, but this is a black and white spotted koi, so I can't tell if it's anything to be concerned with.

Now for the weird part.

As I'm holding him, I gently squeeze his abdomen, which opened his mouth. When I let go, the mouth closes. Simply pressure, I tell myself. So I do this a few more times, and I notice him twitch. Leaving my hand in the water, I continue this "Fish CPR" for a couple minutes, and he begins breathing on his own. I hold him in my hand a while longer, and gently release him.....and he swims away like normal.

Now, I admit that I am not satisfied with this. SOMETHING caused him to go catatonic. Water chemistry seems acceptable:

Ammonia - 0.25 or possibly 0.50, which is a little high, but the temperature is only in the mid-70's
Nitrites/Nitrates - 0.00
pH - Looks to be the high 7's to low 8's

Now, I admit that I don't know how long he was floating like that......my guess is that it couldn't have been too long or else he wouldn't have revived. THE ONLY THING I DID was I added 5 gallons of new water to the system (treated with the recommended dosage of Stress Coat + to remove clorine/chloramine). Keep in mind that the tank itself has about 80 gallons of water in there, and I added this mere five gallons of water through a slow siphon (not just dumped in there).

So I don't know if THAT did anything, but it seems doubtful that such a small amount of water (compared to the existing water in the system) would have shocked that fish.

Any ideas? My questions are as follows:

- Aside from any disease explanation, do you know of anything that would cause a fish to go into this catatonic shock? Again, I thought he was dead (and may very well have been) until I squeezed him back to life).

- Had I not stepped in, do you think the fish would have naturally recovered? I have never seen a fish do this before. I almost dipped him in an immediate SALT DIP (3% solution) but when he swam off relatively normal, I didn't want to risk shocking him back to death.

Whatever "this" is, I think it may have been what killed most of my other fish, since all of them didn't appear to have any sickness or disease before dropping dead.