Help Stuck Out Gill

[tiger-trouble]

hi i have a group of 6 tiger barbs in an aquarium and i have noticed today that one of the tigerbarbs has one of its gills sticking out from its normal possition away from the body it dose not have any disscolourration underneath its gill is bright red its breathing is not that irregular and we cant work out what it is??
can some one give us any advice on this please