A newly introduced fish will have a compromised immune system, and if gets inundated by flukes can have a pretty rapid demise. I have seen a handful of instances that match your timing with flukes.
Did you actually SEE any flukes come off? Maybe TJ has super x-ray vision, but I confess I don't see them in your photo LOL. IME flashers are incredibly twitchy and not at all good at settling into a community tank.
It looked like there were some coming off the tail area and possibly from behind the gill plates. It actually seemed as though there was some improvement last night, he was less lethargic and breathing had slowed.
A newly introduced fish will have a compromised immune system, and if gets inundated by flukes can have a pretty rapid demise. I have seen a handful of instances that match your timing with flukes.