Graduate Thesis Or Dissertation
 

Purine deposition in the skin of juvenile coho salmon, Oncorhynchus kisutch

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  • This study was undertaken to quantitatively evaluate the relationship between silvering of the skin of juvenile coho salmon, due to the deposition of the purines guanine and hypoxanthine, and adaptation to seawater. It was hypothesized that maximum purine deposition occurs at the time these fish normally enter seawater, that the retention of accumulated skin purines is dependent on seawater entry and that the quantity of purines stored in the skin is greatest in fish transferred to seawater at or near the normal migratory period. To test these hypotheses, four groups of fish were transferred to seawater at monthly intervals and sampled for skin purines from February through June. Fish held in freshwater served as controls. Skin purine concentration was determined by enzyme assays. Guanine deposition in the skin of fish held in freshwater until April reached a maximum on April 19. Guanine in all treatment fish declined sharply in mid-May. Guanine in the skin of fish transferred to seawater during the course of the experiments increased again by mid-June; no such increase occurred in fish held in freshwater beyond May 17. Hypoxanthine levels were much lower than guanine levels in all treatment groups and fluctuated only slightly from February through June. Skin guanine and hypoxanthine levels at the end of June were significantly higher in fish transferred to seawater in April and May than in freshwater controls. Coefficients of condition of fish in all treatment groups decreased from February through June, but were significantly lower in fish transferred to seawater in February and March than in freshwater controls at the end of June. Percent mortality of treatment groups transferred to seawater decreased as the time of transfer approached June. A biochemical role for purines during seaward migration and adaptation to seawater is suggested. It is concluded that the physiological changes associated with parr-smolt transformation, seaward migration and seawater entry are interdependent processes and that the deposition or re-utilization of skin purines may play a vital role in their successful completion.
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