A couple of years ago i gave some e yellow, red zeb & peacock fry to a friend who is now 13. in the last 8 weeks or so he has been steadily loosing fish. I have never had many fish die of sickness & i am a bit lost on what is causing this due to my fortunate lack of experience with sick fish.
I think it is an internal parasite that is affecting their swimbladder as the tank is well set up, the water conditions are all fine & in the last two years everything has been fine & nothing has changed recently.
they die shortly (12 hours) after the following actions: swimming on their sides, swimming in a corkscrew manner, they get red blood lines along or in patches on their body.
he has treated the tank with drontal & melafix, he feeds top quality foods & keeps up regular maintenance on the tank. he does have them in a small tank & when the deaths began there were far to many fish in the tank but that has now been rectified.