How do plecs breathe and suck at the same time? This is the subject of a study by Tom Geerinckx, Anthony Herrel and Dominique Adriaens published in a recent issue of the Journal of Experimental Zoology.
Loricariid catfishes (plecs) use their mouths as a suction device to enable them to stick to the substrate, but like many other fishes, breathe through their mouths. This creates an apparent paradox: for a sucker to be effective, there should not be any flow of water into the mouth, yet such a flow is needed for the fish to breathe.
The authors resolve this apparent paradox by studying the mechanics of respiration with and without simultaneous suction attachment in the plec Pterygoplichthys disjunctivus. They did so by using external and X-ray high-speed video recordings of three individual fish to characterise the movements of the head structures during attachment and respiration.
The authors found that the plecs were able to modify their breathing pattern (by taking smaller breaths) in order to maintain the use of their mouth as a sucker. A valve in the mouth and the presence of furrows on the lips were also found to be important in limiting and controlling water inflow, maintaining the function of the suction cup.
For more information, see the paper: Geerinckx T, A Herrel and D Adriaens, 2011. Suckermouth armored catfish resolve the paradox of simultaneous respiration and suction attachment: a kinematic study of Pterygoplichthys disjunctivus. Journal of Experimental Zoology 315, pp. 121–131.