Sick Pleco?

it's a common Lila? How old/big is it? Are there any other signs of illness on him? Is he eating? Are the parameters checking out?

dude, he aint sick, you just havent got enough oxygen in the water. add an airstone or 2 to increase aeration. you should see him stop gasping at the top. its happened to mine once before also. another thing, maybe drop the temp a little, not much, but it helps
Justin

are you feeding him enough?

Mine sometimes somes to the top and eats the flake food.

Also, plecos can push air into their attestins, so is he flying to the top, and going back down again? If he is, then it is normal for catfish, but they do it more often is bad water quality

I agree w/ Cheers. Alot of people don't understand about aeration, but the surface of the water must be disturbed. Alot of people fill their tanks all the way up to reduce noise from the filters, but this severly limits oxgenation. So do higher temps. I keep my water level about 1 inch below the filter lips, and recently added an airstone.

Plecos need a higher amount of oxygen than most other fish. That is why you sometimes see them make surface dives(as I call them) as they can take oxygen briefly out of the air. Also, you'll notice cories do it alot too if oxygen levels are low.