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Functional mapping of ultraviolet photosensitivity during metamorphic transitions in a salmonid fish, Oncorhynchus mykiss

Mark E. Deutschlander^*, Danielle K. Greaves, Theodore J. Haimberger and Craig W. Hawryshyn

Department of Biology, University of Victoria, PO Box 3020 STN CSC, Victoria, British Columbia, Canada V8W 3N5

View larger version (18K): [in a new window]   Fig. 1. Illumination of the ventral (A) and dorsal (B) retina. (A) A patch made of black, opaque, vinyl tape was affixed to the ventral cornea using cyanoacrylate glue. The patch was placed over more than half the retina (see side view), to reduce stimulation of the central retina, and the embryonic fissure where ultraviolet corner cones remain resident in all stages of salmonid development (see text). The fibre optic and quartz screen coupler were angled from above the eye, so that the light was incident on the dorsal cornea. The incident light ray shown is not necessarily representative of all light rays emerging from the fibre optic coupler; it is positioned for illustration purposes only. Light rays incident on the lens from above are refracted by the lens such that light will illuminate an area on the ventral retina. Because the stimulus was larger than the pupil of the fish, the configuration shown would result in illumination of the entire ventral retina. (B) A complementary arrangement of the patch and stimulus allowed for illumination of the dorsal retina.

View larger version (28K): [in a new window]   Fig. 2. Spectral sensitivity of fish after 2 weeks of thyroxine, or control, treatment. All spectral sensitivity curves were obtained under a long-wavelength background to isolate the short-wavelength and ultraviolet cone mechanisms (see text). Both control (A,C) and thyroxine-treated (B,D) fish were tested for dorsal and ventral retinal sensitivity (Fig.1). (A,B) Results for dorsal stimulation, and (C,D) results for ventral stimulation. The values are means ± S.E.M. for all fish from each group (filled diamonds, with sample size (N) indicated on each graph). Data were first normalized to 420nm (i.e. sensitivity at 420nm was set to 0 in all fish). Pigment absorptance curves for the ultraviolet cone mechanism (purple dashed line) and the short-wavelength cone mechanism (blue dashed line) were fitted by eye to the averaged data. The resulting function of the linear-additive model for the ultraviolet and short-wavelength cone mechanisms is represented by the continuous black line. The weights determined by the linear-additive model for the ultraviolet (KU) and short-wavelength (KS) mechanisms (see text for further details) are presented on each graph.

View larger version (27K): [in a new window]   Fig. 3. Spectral sensitivity of fish after 4 weeks of thyroxine, or control, treatment. Data plotted as in Fig.2.

View larger version (27K): [in a new window]   Fig. 4. Spectral sensitivity of fish after 6 weeks of thyroxine, or control, treatment. Data plotted as in Fig.2.

View larger version (20K): [in a new window]   Fig. 5. Spectral sensitivity of natural, untreated steelhead smolts. The data for each of four individual smolts are shown separately (two in which dorsal sensitivity was measured and two in which ventral sensitivity was measured). The data have been displaced on the y-axis so that the data from each fish can be easily viewed. The mass of each fish is shown to the right of each data set. Pigment absorptance curves and the linear-additive model were plotted for each individual fish as described in Fig.2, and the values for the ultraviolet (KU) and short-wavelength (KS) mechanisms are also shown for each data set.

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