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Anna, Pet Expert/Biologist
Category: Pet
Satisfied Customers: 11513
Experience:  40 yrs.: herps, pocket pets, rabbits, poultry, dogs, horses. Biology degree. Vet assistant.
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I have several large Koi. I use two ultra violent bulbs in

Customer Question

Hi I have several large Koi. I use two ultra violent bulbs in the summer to avoid parasites. In the water I only use the oxygen aerator. I never lost a fish in the winter. The water in my pond is still cold so I havenot yet turned on the pump. I found one dead Koi over 15" dead floating on side of pond. Half covered with a thick jelly like membrane. It might have been dead a while until I notice it. Can you please let me know if you have ideas about what caused the death ? If there is something in the pond that will be epidemic - what I can do. Should I do a water exchange, put the pump and two bulbs back on and salt the pond ? Or do you think this was a natural death and it did not leave anything behind that can hurt the other full grown 30 or so Koi. Thanks in advance for your help.
Submitted: 1 year ago.
Category: Pet
Expert:  Anna replied 1 year ago.

Hello and welcome. My name is ***** ***** I'm a biologist with a special interest in fish. I'm sorry for the loss of your koi.

This is a particularly difficult situation because we don't know how long the fish was dead. In cold water, a dead fish may be well-preserved, but it will become coated with slime. However, there are also several illnesses and parasites that can cause that jelly-like membrane.

Your instincts are good. You do want to do a water change of about 25%, and get the pump and bulbs operating. Examine all the other fish as closely as possible. If you see any signs of trouble, you'll want to treat with a good medication. If you don't see anything wrong, you'll have to make a decision. You can salt the pond and keep watching. The other option would be to go ahead and treat. If you choose to use medication, don't salt. TetraPond Treatment is a good medication that treats fungal and bacterial infections, and also parasites. It will not treat viral diseases because there are no medications that can do that. when a viral disease is present, we often lose many fish.

Here is a reputable source for the medication.:

This medication is a good one for situations like this, where we don't know what happened. If you have more questions, let me know. I hope all of your fish will remain healthy.


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