Fish Suddenly Died....Any guidance?

[SaffiStains]

Hi everyone,yesterday was a very sad day. My !4" fantail koi died.I know you are all used to more river type species but i need some answers and no one else can provide them to me.Here is what happened.I fed my fishes yesterday morning,they all ate,except my 13" pangasius cat.All my kois were great they were all active during the day.around 3:00pm i heard a long scraping noise i immediately knew a fish was scraping along the gravel substrate.
i saw my 14" struggling.swimming sideways along the gravel. then he went up to the top of the tank,then slowly sank to the bottom of the tank.still breathing.i put my hand in the tank and tried to press lightly on the sides {i thought mybe he was choking i was in a panic} i didn't know what to do so i held him as if he were in his swimming position and very slightly pressed the sides. then i decided to put him in my small quarantine tank so i went to get that removed the filter return and filled up the quarantine tank.then i noticed his gills were not moving.I knew he had died.but i still removed him from the main tank and put him in the quarantine tank and opened his mouth to see if something was stuck.i didn't see anything.Left him there for a couple mins but realised it was over him.I'm sad and even worst i'm confused.Swim bladder diseases can't possibly have done this to him.Any advice?Thank you.

 

[LawdyLu]

It might be swim bladder disease. If it eats pellets, they can get air pockets. If you soak the flakes or pellets beforehand, it helps. If you quarantined the fish, add a little salt and see if it rights itself. Hopefully, it won't take too long for him to be comfortable again. Good luck!

 

[SaffiStains]

My fish died,i suspect he died before i got him in the quaratine tank.i did add salt immediately to the main tank when i saw him swimming in circles.that fish was approx 11-12 years old.i know kois live relativly long lives weel into 20 -30 yrs but it's just sad cause to me he was perfectly healthy that morning,eating well,no streaks on his fins his fins also were perfect,no cuts nothing.but thanx for the reply.