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Rheotaxis and prey detection in uniform currents by Lake Michigan mottled sculpin (Cottus bairdi)

Max J. Kanter and Sheryl Coombs^*

Parmly Hearing Institute and Department of Biology, Loyola University of Chicago, Il 60626, USA

View larger version (27K): [in a new window]   Fig. 1. Average amplitude spectra of digitized anemometer responses to a suprathreshold (15 m s-2 (RMS) at the source) 50 Hz vibrating sphere for four different flow velocities (0, 2, 4 and 8 cm s-1). Each amplitude spectrum represents the average of four spectra, each obtained from repeat measures of the time-waveform at a given flow velocity. (A) Amplitude spectra from normal, experimental conditions. (B) Amplitude spectra from control conditions in which the flow-producing impeller blade was removed from the drive shaft, but the drive shaft motions remained coupled to the water for different motor speeds. Note that 60-cycle electrical noise is inexplicably more prominent for the 8 cm s-1 flow condition in A.

View larger version (24K): [in a new window]   Fig. 2. Frequency distribution of fish orientation relative to the oncoming flow at 0 cm s-1 (A), 4 cm s-1 (B) and 8 cm s-1 (C). An orientation angle of 0° represents perfect positive rheotaxis (fish facing directly upstream). Each dotted line represents the distribution of orientation angles for one of four individuals, while the solid line indicates the mean distribution for all four individuals. Bin width=10°.

View larger version (16K): [in a new window]   Fig. 3. Vector strength (r) as a function of flow speed (cm s-1) for each of four individuals (M6, M7, M10 and M11). The solid heavy line is the linear regression through the data from the four individuals (r2=0.99).

View larger version (26K): [in a new window]   Fig. 4. Frequency distribution of response angles from post-hoc analysis of fish-to-source angles before and after orienting responses. Frequency distributions are grouped according to how responses were judged during the real-time execution of the experiment — i.e. as hits (A) or misses (B) for signal trials, and false alarms (C) or correct rejections (D) for blank trials. Each solid line represents the distribution of response angles (pooled from 4 individuals) for one of four flow conditions (0, 2, 4 and 8 cm s-1). In E, the mean distributions of all flow conditions are plotted for responses judged as hits, misses, correct rejections and false alarms. Bin width=10°.

View larger version (27K): [in a new window]   Fig. 5. Frequency distribution of response distances as in Fig. 4. Bin width=10 mm.

View larger version (22K): [in a new window]   Fig. 6. Signal level (at the source) at threshold (A) and false alarm rates (B) as a function of flow velocity for 5 individuals (dashed lines with different symbols). Mean thresholds in A and false alarm rates in B for normal experimental conditions are plotted as heavy solid lines (N=5).

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