How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Anna Your Own Question
Anna, Pet Expert/Biologist
Category: Pet
Satisfied Customers: 11544
Experience:  40 yrs.: herps, pocket pets, rabbits, poultry, dogs, horses. Biology degree. Vet assistant.
Type Your Pet Question Here...
Anna is online now
A new question is answered every 9 seconds

Eye looks enlarged and protruding on one of my koi fish

Customer Question

eye looks enlarged and protruding on one of my koi fish
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 to hear your koi is having this problem. Some additional information will help me determine the best steps for you to take.Is the fish still eating well?Is it as active as usual?Is anything oozing from the eye?If you are asked to rate my service, please do 't do that just yet since we are just beginning. Thank you.
Expert:  Anna replied 1 year ago.

Hello again. Because I don't want you to have to wait any longer, I'm going to go ahead and answer as best I can without your response to the questions I asked.

There is more than one possibility for what is going on. My first suspicion for what you have described is what is called 'pop eye.' This is not one particular disease, but a symptom that can be caused by several different things. Sometimes it is the result of an injury.Often, it is bacterial. In that case, it is recommended to treat with myxazin. You would need to put the fish in a hospital tank because we don't want to treat the whole pond. Here is a source for the medication:

Pop eye can also be the result of a vitamin A deficiency, but if you're feeding a good commercial food, that is unlikely. Kidney failure can cause fluid to accumulate behind the eyes. Excessive nitrogen gas in the water can be another possibility. This is most likely in ponds where there is a lot of agitation of the water with power jets. Koi do also get actual tumors, which can put pressure on the eye from behind. A less common cause of these problems is a parasite infestation.

As for what you should do, the first step is usually to treat for bacterial infection.. Adding aquarium salt to the water can help in some cases. Add one teaspoon for every gallon of water in the hospital tank. If you want, you can also treat with an antiparasitic, such as Praziquantel, on the outside chance that parasites are to blame. If there is an organ failure, nothing you do will help. If there is an actual tumor, an aquatic vet can remove it, if you want to go that far to attempt treatment. Many fish live comfortably for quite some time with these eye conditions. If yours is eating and active, that may be what will happen. Sometimes an eye actually dries up and dies. A fish can adjust to that. If the eye symptoms are the result of an internal organ failure, other symptoms will eventually appear.

If you have more questions, let me know by clicking on REPLY. I hope this condition will respond to some of the measures above.


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 after you have all the information you need. I will greatly appreciate a positive rating as that is the only way I am compensated. Thank you!