Koi Carp Passed Away

The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.

nrat

Aquarium Advice Newbie
Joined
Jan 17, 2025
Messages
2
Location
UK
Hi All,

Here in the UK just had a big freeze; and thaw. Found my young koi carp seemingly dead. I went to take it out of the pond and realised it was still breathing but not moving.

I brought it inside, with some pond water in a bag, brought the temperature up to around 20'C by slowly adding warm water around the bag. Applied oxygen with a stone at regular intervals but not so much to keep the water agitated continuously.

Its breathing appeared to become more powerful and started using pectoral fins. but no tail/body movement whatsoever, as if paralysed from the waist down.

I transferred to clean bottled water in a glass tank, temp the same as bag, and started an epsom salt bath at around 18h00 yesterday. 7g of epsom salt to 1.5L of water.

By the time I went to bed at 22h00 there was a tiny pink protrusion from the anus, I was worried this may be prolapse, but thought to see in the morning not much else I could do at that time. Applied more oxygen for a few mins.

This morning, at 04h00 I found fishy dead.

On the bottom of the tank was a normal looking poop, and a giant pink thing. I am not certain what this could be? Impacted food maybe? I use reddish sinking pellets but haven't fed since before the first smaller freeze which the fish survived fine.

I have 4 other fish in the pond (2 comets, 2 shubunkin) who have survived 3 winters no problem, the koi carp managed one smaller freeze but not this bigger one.

Any idea what went wrong? Anything I could have done better? Worried about anything transferring to the other fish, although they seem fine.


1) The epsom bath article I read just mentioned adding it to the aquarium, leading me to believe this was used like an additive, rather than a temporary measure. Is it possible that I helped the fish initially but then it died of overexposure to the epsom salt?
2) Any idea what this pink mass might be?
3) One suspicion is there was maybe unconsumed food at the bottom of pond, koi carp ingested too much of this and was unable to digest over winter leading to severe constipation?
IMG_0605.jpg


One can see the mass and then to the right the "normal" looking poop. The mass is nearly 2cm whereas fishy was 8-10cm.
 
To add, I tested all the water parameters yesterday afternoon, after bringing fishy inside, and all were normal.
 
Maybe bringing up the temperature too quickly? A below freezing up to 20C is going to be extremely stressful if done in too short a space of time and temperture shock can and will kill fish. You don't typically want to change a fishes temperature by more than a few degrees per day.

Obviously you don't have control of an outside fishes temperature the way you do in aquariums, however while you might have a big temperature gradient over a year, day to day you shouldn't see that much of a swing. I would expect koi and goldfish to be a little more tolerant of temperature swings though, but 20C feels extreme.

Also koi and goldfish will go into a kind of hibernation when they need to, such as a pond freezing over and they can survive a pretty bad freezing situation. This is probably what you saw. Maybe bringing the fish out of hibernation too quickly killed the fish?

How deep is the pond? Koi ponds in the UK need to be in excess of 1.0m deep.

Do you have a pond heater to prevent to pond freezing over?

I'm certainly not knowledgeable about pond fish, but these are a couple of thoughts that came to mind.
 
I agree with Aiken that it happened too quickly. To bring the fish back, it should have taken days not hours so the fish probably went into shock.
As for the pink thing, it does look like a worm but very possibly just something the fish ate before the freeze. Most parasitic worms are either white or darker red. Unfortunately, without knowing exactly what it is, it's not possible to determine if it's something to worry about. I would suggest once the freeze is over and the fish are back to swimming actively, use a dewormer in their diet to help ensure that the other fish are safe. Fish can live with internal worms for quite some time so no sense doing this before they are active again. (y)
 
Back
Top Bottom