Pressure and Water Flow Patterns in the Respiratory Tract of the Bass (Micropterus Salmoides)

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Abstract
Instantaneous water velocities in the respiratory tract of bass, Micropterus salmoides (Lacepéde), were measured using a fast-responding hot-filmanemometer. The flow velocity wave form varied within the buccal cavity, with lower peak velocities at the back than at the front. Flow velocity in both the buccal and opercular cavities varied over the respiratory cycle, and 80% of signal power in the velocity wave form was between 1 and 10 Hz. Flow within the buccal cavity reached a maximum velocity of 50cms−1 and did not decline to zero, even when differential pressure across the gills was negative. Simultaneous measurement of dimensional changes in the branchial apparatus, pressure and velocity fluctuations showed that gill bar adduction coincides both with the pressure reversal across the gills and with maximum flow velocities in the opercular cavity. The movement of the gillbars during respiration causes flow velocity fluctuation just in front of the primary lamellae and may be an important component of intraoral resistance contributing to the phase differences between pressure and velocity waveforms.