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First published online October 5, 2006
Journal of Experimental Biology 209, 4077-4090 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02487

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The role of the lateral line and vision on body kinematics and hydrodynamic preference of rainbow trout in turbulent flow

James C. Liao

Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA

View larger version (22K): [in a new window]   Fig. 1. Successive ventral view images (100 ms apart) of a trout with an intact lateral line (A), showing an escape response to a sudden jet of water directed at the body from a syringe (asterisk indicates the start of the jet). Images correspond to the black bar on the graph of head velocity shown below (`LL intact'). When the same trout is treated with cobalt chloride to block the lateral line it no longer exhibits an escape response to a jet of water (B, gray bar, `LL blocked pre-experiment'). After the experiment, fish were retested to confirm that the cobalt chloride treatment did not wear off (C, `LL blocked post-experiment'). Scale bars, 1 cm. All values are mean ± s.e.m., N=4 fish.

View larger version (11K): [in a new window]   Fig. 2. Tail-beat frequency, maximum head angle and downstream head distance from the cylinder for all treatments. The x axis (from left to right): experiments in the light with lateral line intact for the first day of cylinder exposure (V+L+1); the same experiments with fish exposed to the cylinder on two consecutive days (V+L+2, see Materials and methods); experiments in the dark (gray fill) with lateral line intact on the first day (V–L+1); experiments in the light with lateral line blocked on the second day (red box, V+L–2); and experiments in the dark with lateral line blocked on the second day (gray fill and red box, V–L–2). Gray lines connect treatments that are statistically significant at P<0.05. Values for control fish that were exposed to the cylinder for one (V+L+1) and two consecutive days (V+L+2) are statistically the same, illustrating that fish do not alter swimming kinematics as a result of previous exposure to the experimental setup. By controlling for prior experience to the experimental setup, kinematic comparisons made between treatments reflect the presence/absence of visible light and the ability to sense flow with the lateral line. (A) Tail-beat frequency does not differ significantly across treatments, though there is a tendency for fish with a blocked lateral line to exhibit slightly higher tail-beat frequencies and variability. (B) Maximum head angles do not differ significantly across treatments, but fish in the dark tend to exhibit slightly larger head angles regardless of lateral line functionality. (C) Fish with a blocked lateral line hold station further downstream from the cylinder than fish with an intact lateral line in the dark, where station-holding is measured as the distance from the tip of the snout to the downstream edge of the cylinder (where L is the total length of the fish). Within lateral line treatments, there is a tendency for fish in the dark to hold station further downstream from the cylinder. All values are mean ± s.e.m., N=16 tail-beats for four fish.

View larger version (13K): [in a new window]   Fig. 3. Body wavelength, body wave speed, and lateral amplitude along the body for all treatments, where L is the total length of the fish. The x axis (from left to right): experiments in the light with lateral line intact for the first day of cylinder exposure (V+L+1); the same experiments with fish exposed to the cylinder on two consecutive days (V+L+2, see Materials and methods); experiments in the dark (gray fill) with lateral line intact on the first day (V–L+1); experiments in the light with lateral line blocked on the second day (red box, V+L–2); and experiments in the dark with lateral line blocked on the second day (gray fill and red box, V–L–2). Gray lines connect treatments that are statistically significant at P<0.05. Values for control fish that were exposed to the cylinder for one (V+L+1) and two consecutive days (V+L+2) are statistically the same, illustrating that fish do not alter swimming kinematics as a result of previous exposure to the experimental setup. (A) Body wavelength and (B) speed of propagation down the body are statistically higher when the lateral line is blocked and tend to increase in magnitude and variance in the dark. (C) Lateral body amplitudes were measured relative to the midline at three locations. Circles represent the tail tip, squares represent the center of mass (COM), and triangles represent the snout. The tail tip and COM amplitudes for fish in the dark with a blocked lateral line (V–L–2) are significantly lower than control fish on day 1 (V+L+1) and 2 (V+L+2), as well as for fish in the dark with an intact lateral line (V–L+1). All values are mean ± s.e.m., N=16 tail-beats for four fish.

View larger version (6K): [in a new window]   Fig. 4. Fish with a blocked lateral line have a lower maximum body curvature than fish with an intact lateral line. The x axis (from left to right): experiments in the light with lateral line intact for the first day of cylinder exposure (V+L+1); the same experiments with fish exposed to the cylinder on two consecutive days (V+L+2, see Materials and methods); experiments in the dark (gray fill) with lateral line intact on the first day (V–L+1); experiments in the light with lateral line blocked on the second day (red box, V+L–2); and experiments in the dark with lateral line blocked on the second day (gray fill and red box, V–L–2). Gray lines connect treatments that are significant at P<0.05. Values for control fish that were exposed to the cylinder for one (V+L+1) and two consecutive days (V+L+2) are statistically the same, illustrating that fish do not alter swimming kinematics as a result of previous exposure to the experimental setup. All values reported are mean ± s.e.m., N=16 tail-beats for four fish, where L is the total length of the fish.

View larger version (37K): [in a new window]   Fig. 5. Digitized silhouette and midlines of a trout (A) entraining and (B) Kármán gaiting around a 5 cm D-section cylinder, along with corresponding ventral view images, from top to bottom (100 ms apart). Flow is from left to right at 2.5 L s–1, where L is total body length. Note that during entraining the body axis is tilted at an angle to the x axis. Midlines of entraining fish demonstrate the lack of axial undulation, in contrast to the large amplitude body undulations seen in Kármán gaiting fish.

View larger version (84K): [in a new window]   Fig. 6. Head location in the flow tank every 5 sec for 1 h (720 data points per fish), where each color represents an individual (N=4 fish). From top to bottom; (A) treatment in the light with lateral line intact (V+L+1), (B) treatment in the dark with lateral line intact (V–L+1, gray fill), (C) treatment in the light with lateral line blocked (V+L–2, red box), and (D) treatment in the dark with lateral line blocked (V–L–2, gray fill and red box). Fish in the light prefer to Kármán gait (A), even in the absence of a functional lateral line (C). Fish in the dark (B,D) prefer to entrain regardless of lateral line functionality. Total body lengths of individual fish are given.

View larger version (28K): [in a new window]   Fig. 7. Regions around a cylinder in flow that trout will either entrain (defined as two rectangular regions on either side of the cylinder, 7x15 cm) or Kármán gait (defined as a single rectangle centered along the midline of the cylinder wake, 10x15 cm). In the light, fish prefer to Kármán gait in the vortex street downstream from the cylinder (black fill) for the majority of the time during a 60-min experiment, especially when the lateral line is intact (V+L+1). Values for fish in the light with an intact lateral line exposed to the cylinder for two consecutive days (V+L+2) are almost identical to those exposed for 1 day (V+L+1), indicating that previous experience in the flow tank does not alter the preference to Kármán gait. In contrast to their reaction in the light, fish in the dark do not spend much time in the vortex street regardless of lateral line functionality (V–L+1 or V–L–2), preferring to entrain (gray fill) just downstream and to the side of the cylinder. The time that fish spent exploring other regions of the flow tank (white) is similar across treatments.

View larger version (60K): [in a new window]   Fig. 8. Downstream position of the head in the flow tank every 5 s for 1 h under different experimental treatments (N=4 fish). (A) Fish that possess both vision and the lateral line (V+L+1) immediately start to Kármán gait in the vortex street at a defined distance downstream of the cylinder (blue shaded bar) and remain there for the entire experiment. Mean downstream positions are shown (vertical, orange solid line; N=4 fish) along with the standard deviation (orange broken lines). The green shaded bar indicates the region that fish occupy when they entrain. Note that the upstream edge of this region (30 cm) is where the downstream edge of the D-cylinder (not shown) is located. (B) In the dark (gray fill), fish with only a lateral line (V–L+1) initially explore the length of the flow tank and occasionally Kármán gait. However, by the last half of the experiment, all fish prefer to entrain. (C) In the light, fish with a blocked lateral line (red box; V+L–2) show both entraining and Kármán gaiting behavior without a dominating preference for either, unlike all other treatments. (D) Fish without vision or an intact lateral line (gray fill and red box; V–L–2), prefer to entrain rather than Kármán gait, much like in B. When fish with a blocked lateral line stray away from `entraining' and `Kármán gaiting' regions they do so throughout the experiment, unlike fish with an intact lateral line.

View larger version (15K): [in a new window]   Fig. 9. Downstream position of the head every 5 s for 1 h for an individual trout, illustrating the role of the lateral line in facilitating exploration of the flow tank. (A; gray fill) In the dark, a fish with an intact lateral line alternately entrains between right and left sides of a cylinder. (B; gray fill with red box) When the lateral line is blocked, the same fish will continue to entrain in the suction region but no longer explores the other side of the cylinder. In the dark, fish do not prefer to Kármán gait in the vortex street.