My plec swims upside down!

[CMC]

I have a common plec in my 55-gallon and in the past few days I've noticed that he swims upside down at the top of the water. He does this most of the day, not just at feeding time. He's always done a good job cleaning the algae off of the plants and glass but I'm starting to wonder if he's sick or starving for oxygen. I have plenty of aeration in the tank and the water parameters are good.

Does anyone else's plec do this?

 

[dolphinstj]

I have seen one of my plecs do it ossationally. Im not sure why but it interested me too. He doesn't do it that often but I have seen it.