Death cause?

[SimonW]

Hello friends:

How are you doing!

Since several years back I have been over-wintering 200-300 big and small koi indoors, and during every winter season one or a couple of koi died. The death ratio is in average like 1%.

I cannot see any visible external damage to thier bodies, so I don't know why. Can it be that they were the individuals with weaker condition, and the less good water quality caused by a much smaller water body is too much for them?

Still I cannot say that the water quality is bad, since I have had koi with heavy mechanical damages that recoved nicely in it without any treatment.

Water parameters has usually been like this:
Ammonia: 0, nitrite 0.2-0.8 ppm (NaCl added to 500 ppm to remody it), nitrate 80-150 ppm, KH 100-200 ppm (kept with baking soda).

Anyway I hope that some knowledgeable friends here can suggest a cuase. Since almost all of them got this upward bent tail when they died, it must be a typical symptom of a specific problem. but what can it be?

The bent tail could show up up to 2 months earlier before death, but among some I had not noticed any bent tails until they died.

Thanks for your thoughts!

Simon

[fly4koi]

Cut it open you would see eggs, I recommend autopsy for learning purposes, explore the egg vent so you know how to unclog next time.

[richtoybox]

Without obvious signs of infection or other symptoms, it is hard to tell the cause of death in all cases. I have had a fish suffer a stroke or heart attack and swim very fast and very erratic for the length of the pond and lay over dead. No signs or symptoms. All animals die at some point, some younger some older.

[aquaholic]

It's probably too late now but I recommend necropsy too. Even if your not sure what your looking at, it's easy to see internal organ failure (mushy soft white tissue instead of firm healthy tissue), excess fatty deposits, enlarged egg poduction, healthy red gill rakers.

The upturned tail is most likely from excess pressure on body cavity - too many eggs. Usually this impacts swim bladder more causing imbalance and floatation issues.