Biochemical Studies on Smoltification of Salmon

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Young anadoromous salmonids are known to migrate from the river to the sea after smoltification (parr-smolt transformation). Smoltification is a complex phenomenon comprised of various morphological, physiological and behavioral changes. In the body13EA\ : 'silvering' phenomenon, guanine is accumulated in the skin under regulation by thyroid hormone. This research is relevant to our basic understanding of the parr-smolt transformation from the point-of-view of biochemical mechanisms.We analyzed serum proteins during parr-smolt transformation (May-June) of masu salmon (Oncorhynchus masou) by two-dimensional polyacrylamide gel electrophoresis and Western blotting using a rabbit antiserum raised against smolt serum. A new protein (mol. wt. 43,000-50,000, p1 5.0-5.5) appeared in serum of smolt but not parr. This protein seems to be a smolt-specific serum protein. Four guanine-binding proteins were observed in parr or smolt serum by immunoelectrophoresis and autoradiography using radioactive guanine. The smolt-specific protein and guanine-binding protein may be related.The correlation between purine nucleoside phosphorylase (PNPase) activity in liver of steelhead trout, Oncorhynchus mykiss, and smoltification stages was studied. It was found that changes of purine nucleoside phosphorylase activity in the liver wer13EA\ : e closely associated with the accumulation of guanine in the skin of steelhead trout. Two separated peaks of activity were found. The first peak occured during March to April and the second peak was seen in late May, which was corresponded to the fi13EA\ : rst accumulation of guanine and the restoration of guanine caused by descalation, respectively. These results strongly suggest that the liberation of guanine in liver was correleated to phenotype of parr-smolt transformation in anadromous steelhead trout.