Fig. 3. Tailbeat differential pressure and water speed versus time for a typical cod (Gadus morhua) swimming in a ‘Brett-style’ respirometer at 5°C. (A) A single increase in the water velocity of 0.3 m s^–1. (B) Repeated smaller increase in water velocity of 0.1 m s^–1. The pressure data were sampled at 63 Hz. The lower traces in A and B represent the water speed setting of recirculating sea water. The upper traces are the tailbeat pressure data. Note the increase in both tailbeat pressure amplitude and tailbeat frequency with increases in water velocity.