Checkered Barb Can't Close Mouth!

Howdy!
I've had 6 Checkered Barbs for around 16 months.  Sitting watching the tank last night I noticed that one of the males can't seem to close his mouth!  He seems a bit lethargic and although he's trying to eat he can't seem to suck any food in.  Firstly, I'm concerned that he'll die if he can't eat.  Secondly, I wonder how it happened.  I know they're rowdy little so-and-sos, but the males have never injured one another before.  All other fish looking and acting fine and normally.
Has anyone any experience of "gaping mouth disease"?

m.d.

What have you fed lately? I feed chopped pea regularly to my fish but some of the harlequins have a tendency to grab a morsel too large or try to cram several pieces in at once, then spend varying amounts of time (usually no longer than an hour or two, though) with gaping mouths, or attempting to rapidly chew interspersed with gaping mouths, before it eventually disintegrates/softens and swallowed.

I've also had goldfish swallow gravel in the past, plus a fish swallow a strand of my hair and struggle in the same way - very unpleasant to witness. Is there any sign of a strand of hair coming out of the fish's mouth, its vent or both? In the case of the goldish, sometimes a bit of head-bashing against the tank resulted in the gravel being dislodged (obviously they did this as distressed by the situation) but, on one occasion, I did attempt to itnervene and use an instrument to remove the gravel but was equally conscious that it might cause the obstruction to go down further - as it happened, possibly because of the stress of the whole situation and my imminent interference, the goldfish managed to spit the offending pieces of gravel back out.

I wouldn't be concerned about the fish not eating for several days - they can last a week or two without food. If food is causing the blockage, it's likely it will be swallowed or spat out in a day or two at most. If it's not food but gravel instead, then putting food in the tank for the others (chopped pea with shell removed might be a wise idea in this case) may or may not be a more attractive option and result in the gravel being spat out or swallowed along with the pea and eventually being passed out the vent.

Well, sad to report that I found him dead in the tank this morning.  Not long after I got them, one of the males developed a fungus moustache.  I treated them (I thought successfully) at that time, but I do wonder now if it's been a gradual consequence of the earlier infection.  I had a wee look at him when I fished him out, and it appears that his mouth may have been somewhat eroded.  Of course, he'd been a little nibbled by the time I found him!  Hard to tell.  All other fish have been fine throughout.  Never nice to lose one...
m.d. 

Sorry to read that too - I agree, it's never nice to lose a fish (and always results in a lot of questionning about potential causes). Glad all the others seem ok but maybe best to keep an eye on them for the next week or too, just to be doubly sure, and treat for fungus/finrot at the first sign of anything untoward in that vein.