Uh oh! Help with Australian Rainbow!

Um, so I don't really know how to explain this one, never seen it before. My girlfriends Australian Rainbow's head seems to be separating from its body. Yes that's what I said! It looks like, what I believe to be, the isthmus is slowly separating away from the head! The fish tries to eat but the flakes just fly out through its gills. It's starting to become pretty skinny now. Anybody heard of this or have any ideas to help out this guy?

Very strange. I did somewhat of an extensive search online and found nothing that would explain the symptom you described. He or she may have already succumbed by the time you read this. If that is the case, in my opinion, I would "disinfect" the tank, any substrate, decorations, and filtration materials before you put another fish into it, I have used just a vinegar scrub or bath with a good rinse and let dry for a a week or two. It's very difficult to know if it's bacterial, viral, parasitic, or a host of other fish diseases. If he or she is still alive I wouldn't know where to start in-regards to any type of medication treatment. However, in my opinion, I would do a few 4 or 5 20-25% water changes over the next couple weeks, don't over feed do 1x lightly a day or 2x very lightly, keep lights off, if your substrate is of larger diameter or grain or even sand vacuum 1/2 when doing a water change and the other half next water change, rinse out any sponge type filtration material every 3 or 4 water changes, very little stress. Beyond all of that I don't know what else you can do. These are all good husbandry practices as well for a healthy tank with the exception of frequency of water changes (1x a week or every other week depending on tank size and bio load) If it has died and you start over with a new fish, assuming it was the only fish, cycle, cycle, cycle the tank. Also try to setup a quarantine tank with sponge filter and heater in a 10g with same temp as future home, this saves a lot of heartache down the road when a tank full of fish become affected. I don't know the experience level of yourself or your girlfriend but there is plenty of info online as well as this forum on cycling, setting up quarantine tank and any other fish related info. Also when your asking for help or seeking info on your tank or fish it is good to know size of tank, filtration, temp, and fish load. Good luck and remember this is only my opinion others may chime in and give you there opinion.

Any updates on the Rainbow? I haven't seen this issue before so am curious. I have a few rainbows myself so hopefully never need to deal with this issue.