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SE Temple, TJ Haimberger, CW Hawryshyn; The Labile Pigment Pair System in Coho Salmon (Oncorhynchus Kisutch) . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4547.
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Purpose: Migratory pacific salmonids have a labile pigment pair system that shifts from predominantly porphyropsin (3,4-dehyrdoretinal based pigments) in the freshwater system to predominantly rhodopsin (retinal based pigments) when they migrate to the open ocean . This shift in chromophore is thought to be a preemptive transition that prepares the fish for the blue shifted photic environment at sea. Chromophore shifting is coincident with the process of smoltification, which includes other physiological changes such as silvering (the increase in spectral reflectance of the skin pigments) and the ability to hypo-osmoregulate. Methods: Coho salmon were collected from two hatcheries that differ markedly in photoperiod, temperature and upstream distance from the ocean, as well as from the wild in the vicinity of the two hatcheries. A sample of 500 coho were collected from one of the hatcheries on the day of release to the ocean and divided into two identical tanks, containing salt water or freshwater. A sample of 10 to 20 individuals were collected from each location at regular intervals for the period of a year, and wild samples were collected at haphazard intervals. The spectral absorbance of a sample of rods taken from the dorsal hemisphere were measured using charge coupled device microspectrophotometry (CCD MSP). The speed of this device facilitated the large number of samples that were needed to follow the trends over a full year. Furthermore, the CCD MSP system made it possible to take multiple measurements on a single rod photoreceptor, without substantial bleaching effects on successive absorbance spectra. Results: The percentage porphyropsin in the rods of coho parr was higher in the winter months and in systems kept at colder temperatures. The percentage porphyropsin decreased to a minimum during mid summer. For the comparative study between coho kept under matching conditions but in salt and freshwater it was found that those in saltwater showed a rapid decrease to a stable state around 25% porphyropsin, while the freshwater individuals reached this state more gradually. Those kept in freshwater closely matched the wild samples for this vicinity. Conclusion: The shift in the visual pigment system appears highly correlated with photoperiod and temperature. Surprisingly, there was a high degree of variation in the percentage of 3,4 dehydroretinal between rod photoreceptors found in the same location within one individual, and nearly as much variation within an individual rod. Funding was provided by NSERC/SSHRC through the Coasts Under Stress project, and a NSERC equipement grant (CWH).
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