Fig. 4. Relationships between the tailbeat characteristics and swimming speed for cod and plaice swimming at various heights, h, above the bottom. (A) Tailbeat frequencies (F) of plaice (filled diamonds) at h=0 mm and the best-fit linear regression (solid line); F=(2.46±0.60)+(0.041±0.012)u, r²=0.58, P=0.003, N=62. Mean tailbeat frequencies of cod (crosses; means ± 2 S.E.M.), averaged for 5 cm s^-1 speed bands, for clarity, for all values of h combined. The best-fit linear regression (dotted line) is described by: F=(1.31±0.17)+(0.046±0.005)u, r²=0.72, P=0.003, N=158. (B) Tailbeat frequencies of plaice (means + 2 S.E.M.) were independent of speed for h10 mm. Values averaged for all speeds are shown for h=10 mm (N=72), 50 mm (N=64) and 100 mm (N=71). (C) Tailbeat amplitudes of plaice (means + S.E.M.), which were independent of speed for all heights, are shown for different values of h. (D) Mean tailbeat amplitudes of cod (crosses) (means ± 2 S.E.M.) are shown, averaged for 5 cm s^-1 speed bins, for clarity, for all values of h combined. (E) Values for the span (B) of the caudal fin. Values averaged over all speeds for cod and plaice at four different values of h are shown because B was independent of speed and h. Values are means + 2 S.E.M.