Open gill on one side, looks inflamed

[Alix2c]

So I have a comet goldfish I’ve had for 4 years. He’s in a 55 gal.

i noticed recently that his gill only on one side was sticking out.... I don’t see anything on his gills that’s outside of his body but a little white and it doesn’t look like worms or balls or anything. Just like his gill is also white/red. I will attach photos.

i have no idea what it could be. Please help 

bare with me, I can’t get a great picture 

[Arctic Mama]

Hey there! Sometimes that happens because of flukes or ammonia poisoning, if you can fill out our diagnostic form in detail we can help you figure out which it might be

 

Test Results for the Following:

* Ammonia Level(Tank)

* Nitrite Level(Tank)

* Nitrate level(Tank)

* Ammonia Level(Tap)

* Nitrite Level(Tap)

* Nitrate level(Tap)

* Ph Level, Tank (If possible, KH, GH and chloramines) 

* Ph Level, Tap (If possible, KH, GH and chloramines)

Other Required Info:

* Brand of test-kit used and whether strips or drops?

* Water temperature?

* Tank size (how many gals.) and how long has it been running?

* What is the name and "size of the filter"(s)?

* How often do you change the water and how much?

* How many days ago was the last water change and how much did you change?

* How many fish in the tank and their size?

* What kind of water additives or conditioners?

* What do you feed your fish and how often?

* Any new fish added to the tank?

* Any medications added to the tank?

* List entire medication/treatment history for fish and tank.Please include salt, Prazi, PP, etc and the approximate time and duration of treatment.

* Any unusual findings on the fish such as "grains of salt," bloody streaks, frayed fins or fungus?

* Any unusual behavior like staying at the bottom, not eating, etc.?