Optical properties of the pineal window of Atlantic salmon (Salmo salar L.) |
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Authors: | Trond Nordtug Ole Kristia Berg |
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Institution: | (1) Department of Zoology, University of Trondheim, N-7055 Dragvoll, Norway |
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Abstract: | The spectral composition and intensity of light penetrating different parts of fresh preparations of the upper part of the
skull of Atlantic salmon (Salmo salar) (fork length 25–30 cm) was investigated. All measurements were made in an aqueous medium, by moving the tip of an optical
fibre in a three dimensional lattice below preparations that were illuminated by a parallel light source from above. The intensity
of the transmitted light showed a well-defined maximum just below the pineal groove. Light that penetrated the skull from
a source vertically above was refracted to produce a focusing point in the approximate position of the pineal body. Light
projected from angles of 45° relative to the vertical position was only slightly (25%) attenuated, thus indicating a wide
acceptance angle.
There was an almost uniform transmission of light (of 3%) between 500 and 700 nm. The transmittance of UV light (350 nm) was
about 10% of that of green light. These differences are small when compared with the intensity range reported for the pineal
light receptors. The transmission properties are discussed in relation to the known diurnal changes in the spectral composition
of natural light. |
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Keywords: | pineal organ light absorbance transmittance skull head rhythms photoperiod zeitgebers |
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