[Shonick2]

When I bought it, the goldfish's tail and koi's tail are all clear.

I quarantined these fishes. After like 3 weeks, I saw the red vein on the tails of goldfish and koi.

Since I saw these red vein, I continue keeping these fishes in the quarantine tank with salt. There is time I used paraguard and melafix as well.

They have been in my quarantine tanks for over 2 months. The temperature is getting colder and I am unable to put them in my Koi pond.

Is this really a disease? The fish with number 3 is in a separate tank, and it has more red vein than other fishes in other tanks.

Are they contagious?

Can the colder weather cause these? My area temperature lately around 50- 55 degree at night for the last 30 days.

Please help me, I really want to put these fishes into the pond before the winter. I have 10 other fishes in the pond right now. I don't want them to get this disease if it is contagious.

Please see it in the attached picture. I circled the red vein.

Thank you very much for your help.

 

[Kubla]

I can't see anything in the pic that looks to be an issue. Where are you located? If you can keep a hole in the surface ice of your pond then it's not too cold for goldfish or koi. Just don't let the surface freeze solid they need a vent.

 

[Shonick2]

These fishes are in the quarantine tanks, 10 to 30 gallons tanks. I change water every day or other day.

They are not in the pond yet because I do not want them to infect other fishes in the pond.

The issue is the red blood vein show up in their tail. It is very hard to see clearly on the pictures, that is why I circled it, so you can look at it closely.

 

[ichthyogeek]

It could just be a random red vein. The fish looks healthy (fins are splayed and not clamped); is it eating normally, defecating normally, and otherwise acting like a normal healthy fish does?

 

[Shonick2]

It look very normal to me. The only sight is red vein on their tail.