Fish may be stressed - could because of disease, or if you're putting your hand in there too much
Not enough oxygen in the water - do you have something to disturb the surface of the water? A simple hang on the back filter you can buy at Walmart does the trick, air pumps can work (though rarely seen in saltwater).
Did you just add the fish? Are they hanging out near the top of the tank? Do you yell at them a lot....? Need more info