Hi,
This is my first post here. I am posting because I recently lost all 8 of my threadfin rainbowfish. I have several tanks, but this one is a 125gal tank with a variety of fish. It is primarily clown loaches, bosemani rainbowfish, cherry barbs, and odds and ends from other tanks. The threadfins were added a while ago. I can't tell you exactly how long, but they were all doing fine for several months. Then I noticed one sort of stuck at the top having trouble swimming down. I'm sorry, but I never took a picture. At this time, I also counted closely and noticed I had already lost at least one. Over the course of a week, I saw two more fish do the same thing. I started treating with antibiotics (Maracyn) at this time. After the treatment, I ended up with 3 left and they seemed OK. Those three went over a week with no issues. Unfortunately, I came home to find two gone a few days ago... and the last yesterday.
The tank parameters are: 7.6-7.8pH, nitrates usually ~50, no nitrite or ammonia. Hardness about 6-7 degrees and buffer 2-3 degrees- basically my tap water. The tank is at 80F.
I really wish I had a picture for everyone, but I don't. The fish showed no signs of other issues. They would just get sort of stuck at the surface, unable to swim down. Eventually they would end up nose-down and have sort of a hunched over back, and then pass. I recently read it might have something to do with food, so for reference I feed the tank a wide variety of food, but the only stuff they ate was crushed up extreme flakes and extreme nano pellets. And I did observe they would all eat... until they got stuck at the surface and really couldn't any more. All 8 were roughly full grown when I got them, so age isn't out of the question - but I find it odd that 8 would go within a few weeks of each other due to age.
There's nothing to be done now, but I'd really like to know if anyone knows what happened. And if it may resurface in other species in this tank. I'd hate to lose my bosemani... they're big and I've had them for a long time.
Thanks for any help.