The water flow through the gills in lampreys is
modified in order to be compatible with their
specialized suctorial feeding mechanism (Randall,
’72). Lampreys are parasitic, and when their
disc-shaped mouths are attached to a host fish or
to the substrate, the water flow via this route to
the gills is blocked. The lampreys make use of
their external branchiopores for both water
inhalation and exhalation (tidal breathing) (Fig.
1f). They have also been observed to draw water in
through their first few anterior pouches, which is
then exhaled through their posterior pouches
(Nekvasil and Olson, unpublished observations).
The lattice-like cartilaginous skeleton supporting
the pouches and a well-developed musculature
produce the pumping action to circulate the water
in the gill pouches.