you don't give any information about your aquarium (filtration, etc..) Not knowing what equiment you have, it's hard to offer advise that directly applies to your set up. Simply put, The surface of your water needs to be disturbed one way or another to de gass (oxygenate) your water. Several good options were offered by other peoples post here. Bubbles in your water do very little to oxygenate your water, it's when the bubbles hit the surface and disturb the surface of your water that de gassing occours. Power heads (as some one else mentioned) aimed at the surface will agitate the surface of the water and cause de gassing. Basically do something with your equipment to agitate the surface or your water. Also, if you have not all ready, make sure your water quality is good. By this I mean test it, not look at it and dertermine it's ok because it's clear. If you have ammonia or nitrites (espcially nitrites) this often will cause fish to have labored breathing.