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First published online September 5, 2008
Journal of Experimental Biology 211, 2950-2959 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.020453

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Swimming kinematics and hydrodynamic imaging in the blind Mexican cave fish (Astyanax fasciatus)

Shane P. Windsor^1,*, Delfinn Tan¹ and John C. Montgomery^1,2

¹ School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
² Leigh Marine Laboratory, University of Auckland, Private Bag 92019, Auckland, New Zealand

View larger version (9K): [in this window] [in a new window]   Fig. 1. Experimental setup to record swimming kinematics of blind cave fish using digital video cameras. Setup shown is for head-on trials. Setup for parallel trials was similar except the divider in the centre of the tank was not present. (A) Side view. (B) Top view.

View larger version (16K): [in this window] [in a new window]   Fig. 2. Image processing algorithm to extract kinematic parameters from far camera footage. (A) Original image. (B) Image with background subtracted. (C) Result of thresholding by intensity. Skeletonised midline shown with measurements D1 and D2 of body width one-sixth of the way down the midline from each end. The wider end was taken to be the head. (D) Fitted midline approximation with the first third linear and the remaining two thirds represented by a fifth order polynomial. The centre of area is marked by X and the nose of the fish by O.

View larger version (5K): [in this window] [in a new window]   Fig. 3. Parameters measured in head-on approaches where fish avoided the wall. The first sign that a fish had detected the wall was the rapid extension of the pectoral fins (solid outline). At this point the orientation of the fish relative to the wall () was measured by fitting a straight line to the position of the fish's nose in the previous four video frames (dashed outlines). The distance between the wall and the nose of the fish (d) was also measured down this line. The velocity of the fish (v) was calculated from the nose position using B-spline fitting by generalised cross-validation and taking the first derivative.

View larger version (22K): [in this window] [in a new window]   Fig. 4. Kinematic parameters measured from far footage of parallel trials. (A) Image series of a blind cave fish swimming along a wall showing the corresponding kinematic parameters. (B) Velocity of the centre of area of the fish. (C) Tail angle of the fish; tail beats to the left correspond to negative angles, those to the right to positive angles. (D) Swimming phase classification based on tail angle and the rate of change of tail angle (not shown). Double refers to a tail beat on both the right and left sides of the fish, single left and single right refer to a tail beat on one side of the fish only. (E) Classification by location in tank.

View larger version (31K): [in this window] [in a new window]   Fig. 5. Series of images from close camera footage of a head-on trial with a fish approaching the wall and avoiding collision. The fish glides towards the wall, then at 100 ms extends the pectoral fins away from the body; at this point the nose is 2.7 mm away from the wall. The fish then curves its body to the left, turning to follow along the wall, without making any contact. Length of scale bar is 1 cm.

View larger version (5K): [in this window] [in a new window]   Fig. 6. Histogram of the distances at which the fish appeared to respond to the wall by initiating a tight turn when approaching head-on. Grey bars represent avoidances, black bar represents number of collisions with the wall. Approaches of all fish pooled (N=12).

View larger version (9K): [in this window] [in a new window]   Fig. 7. (A) Mean distance at which fish reacted to the wall plotted against body length. (B) Mean distance at which fish reacted to the wall plotted against the mean velocity that the fish was swimming at. Error bars show s.e.m. Number of approaches per fish ranged from 6 to 21 with a mean of 13.

View larger version (18K): [in this window] [in a new window]   Fig. 8. Series of images from close camera footage of a head-on trial with a fish colliding with the wall. The fish starts a tail beat as it approaches the wall and shows no sign of detecting the wall before it collides with it. After colliding with the wall the fish turns to the left and swims along the wall. Length of scale bar is 1 cm.

View larger version (27K): [in this window] [in a new window]   Fig. 9. Series of images from close camera footage of a parallel trial showing pectoral fin contact with the wall. The fish is gliding along the wall (line near bottom of images) then beats its tail to the left side of its body. At the start of the tail beat the pectoral fins are extended and the right fin makes contact with the wall. This lasts for 60 ms before the fins are retracted as the fish finishes the tail beat and resumes gliding. Length of scale bar is 1 cm.

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