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Kinematics of plaice, Pleuronectes platessa, and cod, Gadus morhua, swimming near the bottom

Paul W. Webb^*

School of Natural Resources and Environment and Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109-1119, USA

View larger version (35K): [in a new window]   Fig. 1. Swimming speeds at which fish began to swim and 10-min critical swimming speeds (ucrit) for cod, and for plaice at various heights, h, above the bottom. Values are means + 2 S.E.M. Sample sizes are given in Table 1.

View larger version (28K): [in a new window]   Fig. 2. Tracings of the centerlines of the body of cod and plaice swimming at 35 cm s-1. Observations are shown for plaice swimming at the ground (0 mm) and at a height of 50mm. Centerlines are shown for 1/30 s intervals.

View larger version (18K): [in a new window]   Fig. 3. The distribution of amplitude, H, and span, B, along the length of swimming cod (N=9) and plaice (N=10). (A) Specific amplitudes of cod at all values of h, (B) specific amplitudes of plaice, (C) specific spans of cod and (D) specific spans of plaice. Amplitudes, and the span of the body and fins, are normalized to total body length (L). Locations along the body length are normalized to total length as relative position along the body. Data in B are shown only for plaice swimming at the bottom and at a height of 50 mm for clarity. Values are means ± 2 S.E.M.

View larger version (29K): [in a new window]   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.

View larger version (19K): [in a new window]   Fig. 5. The relationships between total mechanical power, P, and swimming speed for cod and for plaice swimming at heights, h, of 0, 10, 50 and 100 mm above the bottom. Although plaice only swam at current speeds >15 cm s-1, the power curves have been extrapolated to lower speeds for comparison with cod.

View larger version (17K): [in a new window]   Fig. 6. The relationship between the gap/span ratio (z/B) and total mechanical power for plaice swimming at speeds of 5-45 cm s-1. Results are shown for (A) the tail and (B) the non-re-entrant portion of the body and median fins at the maximum span, Bmax.