The movement of water across the gills of non-ramventilating
fishes involves the action of two pumps: a
pressure pump that pushes water across the gills from the
oropharyngeal to the parabranchial cavity, and a suction
pump that draws water across the gills from the
oropharyngeal into the parabranchial cavity. Together, the
two are thought to keep water flowing continuously anteroposteriorly
through the head of the respiring animal.
However, there is evidence that the pressure and suction
pumps do not always work in perfect phase in
elasmobranch fishes, leading to periods of higher pressure
in the parabranchial than in the oropharyngeal cavity.
We investigated the existence and consequence of such
pressure reversals in the hedgehog skate Leucoraja
erinacea using pressure transducers, sonomicrometry and
flow visualization including internal visualization using
endoscopy. We noted four patterns of respiration in the
experimental skates distinguished by the flow pattern at the
three openings into the respiratory system: (1) in through
the spiracle only, (2) in through the mouth + spiracle