What is wrong with my glo fish?

[liddlelady1]

Last night i bought some glo fish to add to my fish tank. After getting them home and letting them sit i put them in the aquarium, when they started swimming i saw that one particular glo fish had its mouth open. There are two yellow green ones three pinkish and an orange one. The one pink one is the only one with this problem, ive monitored it throughout the day and it has not closed. What is wrong with it, and will it die?
The tank is fine, it has a heater, and a filter and i had the water tested.