mouth opening and closing rapidly?

[liuj1]

It seems that one or two of my fish are opening and closing their mouths rapidly. What does this indicate? Methinks it's poorly oxygenated water, but is it something else?

[JSchmidt]

Insufficient oxygen, ammonia or nitrite poisoning... could be a number of things. How are water parameters?

Jim

[NatakuTseng]

Also if you could what species the fish is, and the tempature of the tank.