VISUAL ORIENTATION AT THE WATER SURFACE BY THE TELEOST ZENARCHOPTERUS

¹ Biology Department, Yale University, New Haven, Connecticut 06520

1. Visual orientation of the surface-living hemirhamphid teleost Zenarchopterus has been studied with individual fish swimming in an experimental vessel open to the air. Measurements of spontaneous heading preferences were made in the afternoon and morning respectively of two successive days, during which the sun's bearing differed by nearly 180°. Fish were tested under natural illumination of sun and sky as well as with six different e-vector directions of imposed linearly polarized light.

2. Data were selected among other things on the criterion that maintenance of a given azimuth direction ± 20° for a 10 sec period counted as an oriented response. Comparison with the distributions of the total measurements justifies this selection.

3. Zenarchopterus avoided the azimuth quadrant towards the sun. This suggests negative phototaxis but other explanations are possible.

4. A strong southerly heading preference occurred on both days under natural illumination by sun and sky. The same marked preference is also evident in the with-polarizer data plotted relative to North. This persists in the residual data when the counts are subtracted for the N-S imposed e-vector which parallels the sky polarization in the sun's vertical.

5. Such orientation occurred while the sun's bearings were constant: when solar bearings were changing rapidly orientation was less clear or absent. These results support a time compensated sun compass orientation.

6. Responses to imposed polarization patterns show a strong preferential orientation parallel to the e-vector. This persists when the N-S imposed e-vector counts (which demonstrate strong southerly preferences parallel to the sky polarization in the sun's vertical) are subtracted from the overall data. Comparison with previous underwater experiments on the same species indicates that these water surface data yield stronger polarotaxis and may provide better evidence for normal behavior.

7. The correlation of a menotactic azimuth preference parallel to sky polarization in the sun's vertical with strong polarotaxis parallel to the e-vector provided by a polarizer suggests that responses to natural polarized light may be involved in normal direction finding by Zenarchopterus.

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				D. H. Taylor and K. Adler Spatial Orientation by Salamanders Using Plane-Polarized Light Science, July 20, 1973; 181(4096): 285 - 287. [Abstract] [PDF]