Retinal Responses in Pacific Salmon (Oncorhynchus masou) Fry to Weak Magnetic Fields and Ultraviolet Light

Abstract

Pacific Ocean salmon (Oncorhynchus masou) fry aged six months mounted specific, previously undescribed, responses to exposure of retinal photoreceptors to ultraviolet light (UVL) in different combinations with a constant magnetic field (MF) (80 G). After exposure to UVL for 2 h (experiment 1), the pigment index (PI) of the retinomotor response increased from 0.30 ± 0.10 to 1.31 ± 0.20. Rods were present in the pigment layer, while cones were only partially screened by pigment. Overall, the retina demonstrated the twilight (mesopic) reaction. After exposure to UVL for 2 h followed by exposure to an MF with a constant magnet for 2 h (experiment 2), PI increased to 2.08 ± 0.10 and mean myoid height and the mean diameter of double cones increased. The retina showed a photopic response. Experiment 3 (MF for 2 h, followed by UVL for 2 h) gave the smallest PI values, 1.28 ± 0.12. Mean myoid height decreased, while mean cone diameter did not change. The retinal response was scotopic (as in the dark). Our own results, along with published data, led to the conclusion that MF distorts the influence of UVL and leads to unusual retinal reactions. These results support our previously described variant of the light-dependent magnetoreception model for vertebrates.