Functional Morphology of the Urohyal Shunt for Symmetrical and Asymmetrical Ventilation in the Flatfish, Isopsetta isolepis.

Flatfishes are benthic fishes that are well known for their ability to bury in the sediment, making the transition from above to below the sediment in a matter of seconds. Laterally flattened bodies allow flatfishes to lay flush against the substrate, a behavior facilitated by having an asymmetrical neurocranium with two eyes on one side of the head. Despite neurocranial asymmetry, their gill chambers are highly symmetrical. Additionally, most flatfishes have a uniquely shaped urohyal bone that forms passageway for water to travel ventrally between the "eyed-side" and "blind-side" gill chambers. Our study examines whether the kinematics and pressures generated by the gill chambers are also symmetrical during breathing above and below the sediment and during rapid burial in sediment. We studied Isopsetta isolepis individuals using sonomicrometry crystals to measure the changes in positions of the opercle bones relative to the urohyal and pressure transducers to record gill chamber pressures during burial. We conclude I. isolepis exhibit both symmetrical and asymmetrical breathing above and below the sediment. Pressures and movements were highly asymmetrical during burial jetting. We observed motions that indicate that the urohyal is an active shunt to allow passage of water between the eyed to the blind-side gill chambers.