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Anna, Pet Expert/Biologist
Category: Pet
Satisfied Customers: 11071
Experience:  40 yrs.: herps, pocket pets, rabbits, poultry, dogs, horses. Biology degree. Vet assistant.
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I have just lost 1 fish, and I now have another with the same

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I have just lost 1 fish, and I now have another with the same symtoms both are koi.
The fish are sluggish, hardly moving around, not feeding, the one that died was gapping at the surface
I have checked the water quality, it seems fine, there is plenty of oxygen getting into the pond through three different methods
all the other fish seem fine at the moment
there wasn't a mark on the one that died to show there was anthing wrong


My name is XXXXX XXXXX I'm a biologist with many years experience keeping fish.. I'm sorry to hear of the loss of your koi.Some additional information will help me figure out what might be wrong.

What numbers did you get when you tested the water- ammonia and nitrites in parts per million (ppm) and for the pH?

What is the water temperature?

Check the sick fish very carefully. Do you see red veins in the fins or tail?

How big is your pond (liters or gallons)? How many fish are in it and how long are they (head to tail tip)? How long has the pond been established?

Thank you.


Customer: replied 3 years ago.

Water tests where done with the simple colour charts.

water temp 20 degrees +

haven't seen any red veins ( it is night time here so can't check.

pond is 2300 gallons

6 x Koi about 8 to 14 inch long

7 x shubumkins 4 to 6 inch long

20 to 40 shubumkin fry from 1 to 3 inch long

Thank you for getting back to me. Unfortunately, those test strips are often very inaccurate. However, for ammonia and nitrites, what range did they show? For example, zero, safe, etc.?
Customer: replied 3 years ago.

both where zero

Customer: replied 3 years ago.

Both where Zero

That's great. While I was waiting, I calculated your inches of fish per gallon of water and that is fine, too. The water temperature is perfect. Since two fish ahve died with no symptoms other than lethargy and gasping for air, we have to assume there is something internal causing the problem. There ares several possibilities. There are some viral diseases of koi that cause death by destroying the internal organs. Fish often die with no signs of anything being seriously wrong. These diseases are more likely if you have added new fish in the last few months. There's a slight chance that birds or frogs can transfer it from one pond to another. If this is what's wrong, there is nothing you can do. In that case, more koi will come down with the virus, but the goldfish will not.

Another possibility is that the fish have a parasite not visible to the naked eye. Gill flukes are one that could cause these symptoms. The flukes are microscopic, so you can't see them. Adding pond salt is a good idea because it will help the fish with stress, but it won't actually treat any disease. Often, when gill flukes are present, a bacterial infection is also involved. The recommendation is to first treat with an antiparasitic. I like Praziquantel, which should be available in any pet store.Treat once according to the directions, then follow up with a second treatment 4 days later. After the second treatment, do a water change, then treat with an antibacterial. A combination of Melafix and Pimafix is good. Another good solution when we can't be sure of a diagnosis is to treat with TetraPond Pond Fish Treatment, along with the salt.. It treats a range of problems encountered in pond fish. If a virus is responsible, however, it will have no effect. Here is an online source. They do ship internationally, but there would be increased shipping costs.

You've already taken a good step by increasing aeration. I would also do a partial water change of about 10%. Then add the salt. If the sick fish isn't better in 24 hours, go ahead and either treat the pond or move that fish to a hospital tank to treat with medications.

If you have more questions, let me know in a REPLY. I hope this will turn out to be something treatable and your fish will recover.


My goal is to provide you with excellent service – if you feel you have gotten anything less, please reply back, I am happy to address follow-up questions. Please remember to rate my service only after you have all the information you need. Thank you!
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