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Spatial variation in fast muscle function of the rainbow trout Oncorhynchus mykiss during fast-starts and sprinting

D. J. Ellerby^* and J. D. Altringham

School of Biology, University of Leeds, Leeds LS2 9JT, UK

View larger version (24K): [in a new window]   Fig. 1. Myotome 15 of the rainbow trout Oncorhychus mykiss. The surrounding myotomes have been removed to reveal its structure and relationship to the axial skeleton. Fibres tended to be oriented so that they were directed towards the apices of the anterior- and posterior-pointing cones. The circles indicate the locations of the measurement points.

View larger version (17K): [in a new window]   Fig. 2. The relationship between peak lateral deflection of the tail tip and tailbeat frequency. Peak deflection was measured as the perpendicular distance to the swimming track during straight-line swimming. Each data point represents a steady swimming sequence from a different unwired individual (N=20). FL, fork length. See text for further details.

View larger version (24K): [in a new window]   Fig. 3. Fish outlines during sprinting (A) and a C-start (B). Outlines were traced at 20ms intervals during sprinting and at 10ms intervals during the C-start. The outline highlighted in red shows the small initial movement contralateral to the C-curve.

View larger version (16K): [in a new window]   Fig. 4. Muscle strain in the superficial anterior-pointing cones at three points along the body during sprint swimming. Strain is expressed as the percentage length change ±l0, where l0 is muscle resting length. Blue, red and green points represent data from 0.35, 0.5 and 0.65FL respectively, where FL is fork length. Values from different fish are shown with different symbols. Data are from six fish, with five measurements from each individual. The solid line is the significant relationship for 0.65FL (see text for further details).

View larger version (32K): [in a new window]   Fig. 5. Representative fast muscle strain and EMG traces from three points along the body axis during sprinting at approximately 12Hz. Measurements were taken at 0.35, 0.5 and 0.65FL, where FL is fork length, from the snout in the superficial anterior-pointing cones of the myotome. Strain is expressed as the percentage length change ±l0, where l0 is muscle resting length.

View larger version (23K): [in a new window]   Fig. 6. The relationship between phase of EMG activity and tailbeat frequency during sprinting. Onset and offset times of EMG activity are relative to the sinusoidal, 360°, strain cycle. Muscle is at resting length l0 at 0° and maximum length at 90°. Blue, red and green points represent data from 0.35, 0.5 and 0.65FL, respectively, where FL is fork length. Values from different fish are shown with different symbols. Data are from six fish, with five measurements from each individual. Equations for the lines are presented in Table4.

View larger version (30K): [in a new window]   Fig. 7. Fast muscle EMG activity in the posterior-pointing cones (PPCs), the hypaxial muscle and the deep anterior-pointing cones (APCs) of myotome 15. Traces show sprinting at 10Hz and the stage 1 EMG of a fast-start, both in the same fish.

View larger version (23K): [in a new window]   Fig. 8. Simultaneous strain and EMG recordings from the superficial anterior-pointing cones of myotome 15 on both sides of a trout during a fast-start. Strain is expressed as the percentage length change ±l0, where l0 is muscle resting length.

View larger version (24K): [in a new window]   Fig. 9. The relationship between the strain cycle and EMG activity at three points along the body of a trout during stage 2 of a fast-start. Data were obtained from the superficial anterior-pointing cone of the myotome at 0.35, 0.5 and 0.65FL, where FL is fork length. Strain is expressed as the percentage length change ±l0, where l0 is resting muscle length.

View larger version (22K): [in a new window]   Fig. 10. Fast muscle shortening velocity at three points along the body axis during sprinting. Blue, red and green points represent data from 0.35, 0.5 and 0.65FL, respectively, where FL is fork length. Data for carp and scup were derived from Rome et al. (Rome et al., 1992). The solid horizontal line represents the mean fast-start muscle shortening velocity. The dashed horizontal line represents the minimum fast-start muscle shortening velocity. l0 is the resting muscle length. r=0.99, 0.98 and 0.97 for linear regression lines at 0.35, 0.5 and 0.65FL, respectively. For all lines P<0.05 (Pearson product moment correlation).