Unless you have an extremely tall and narrow tank, ie: surface are of the tank is little compared to the volume of the tank, surface agitation by filter outflow will more than likely provide enough aeration to let adequate oxygen diffuse into the water. Higher temperatures decrease oxygen saturation. SW holds less oxygen than FW, I believe. You would have to have a very crowded tank or heavily planted with co2 injection to make oxygen a problem.
But I othwerwise agree with the surface gasping, although I have never seen this.