Field demonstration of polarotaxis in the fish Zenarchopterus
Oriented responses to linearly polarized light have been quantitatively confirmed in the marine teleost Zenarchopterus studied in underwater field experiments with the aid of SCUBA. During six successive mornings 2485 heading measurements were made on 36 untrained fish. With natural illumination spontaneous azimuth orientation is mutiply dependent on the sun's bearing and apparently on the natural polarized light of blue sky or water as well as the direction of the interisland channel where the fish were collected. When a dichroic filter is placed over the fish polarotaxis is manifest as directional preferences mainly perpendicular and less strongly, parallel to the plane of polarization. This response is most intense when the imposed e‐vector differs maximally (by 60°–90°) from that predominant in the natural illumination (90° to the sun's bearing). When the sun's disc is partly or wholly obscured by clouds polarotaxis is significantly weakened even though the polarization pattern visible to the fish through the dichroic filter would be virtually unchanged. More than moderate angular turning rates by the fish swimming in the experimental vessel also weaken their response to the e‐vector. Individual fishes show different reactions: about one‐third of those in full sunlight oriented strongly parallel and perpendicular to the imposed e‐vector, another smaller group appears to orient obliquely to the polarization plane while the remainder respond weakly to the e‐vector if at all. Continuing work is required to demonstrate the physiological mechanism and ecological significance of these behavioral patterns. Copyright © 1972 Wiley‐Liss, Inc., A Wiley Company
