Anorexic fish

It has come to my attention today that unfortunately one of my goldfish is suffering from anorexia. No, it's not a clinical diagnosis as I don't think there are really any vets who treats fish, but more from 'experienced' observations. Afterall, I've kept fish for many a years. And anyways, the fish is so skin-on-bone that anyone can tell it's been without food for extended period (sorry, no fotos. If I have any they wouldn't be very appetising either. Hah, appetising). It's not that I have been neglecting the tv-aquarium while keeping daily watch on the tropical tank, looking at the colours of the fish (and now more frequently and inadvertantly algae on the glass, must clean again), incessantly looking for the newborns (second 'batch' was born last friday, about 3 wks after the 1st. From different mothers of course. Don't know if they survived well 'cos I haven't been able to see the new newborns since. Although, the old newborns went missing for days before finally reappearing, apparently hiding under the pebbles, plastic fake shipwreck, & big giant shell. Oh wait, why am I on fish again? Oh, ok, anorexic. Neglect. Ok.) Well, no, I havne't been neglecting the TV-aquairum in favour of the tropical tank. I've been feeding and cleaning as per normal routine. But for some reason I spent extra minutes just staring at the tank today. Maybe it's because it's due for another clean yet the water's still so clear. But anyways, that is when I noticed the little one looking anorexic. It was feeding day too, so fed as per normal portions. While the others (many of whom have grown to become fatsos in the process) the little one remained uninterested, even if the dried food or blood worms hit it right in the face. Maybe I should put it in solitary confinement for some psychiatric treatment? Will see, will see. But yeah, so now you know. Even fish can be anorexic. Wonder what happens if they become bulimic?