Buccal Opercular Cral cavity G cavity Opercular valve resistance valve Suction Figure 4.4 Diagrammatic represen- pump tation of the wostage (buccal and operuar)pump for ventilating the gills of bony and cartilaginous fishes. The first three phases actively pump water through the gill sieve.The last phase shown (iv)does not pump a Pressure significant flow but accounts for only a pump very brief part of the cvcle.(From Hughes1963.】