Iteroparity of Female Fluviatile Form Masu Salmon, Oncorhynchus masou in a River of the Southern Sanriku District, Honshu, Japan.

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One year or older females of fluviatile form masu salmon were collected from a river in the southern Sanriku district (Pacific side of Northern Honshu) . The observation of their body shape, coloration and ovary revealed their first spawning season occurred in the second autumn.<BR>The empty folicles appeared in most of ovaries of two years or older females. Their oocyte diameters were found to have bimodal distribution and the larger oocyte showed gradual development during the period from early spring to early summer, as cases of one year old fish which had not spawned yet. One spawning mark on the scale was formed in the matured female during spawning season. One or two spawning marks were found in most females of two years or older. Those facts indicate that some females of fluviatile form don't die after first spawning, and continue spawning during two or three spawning seasons and the reproductive traits of fluviatile form are of iteroparity being different from those of sea-run form.
日本水産増殖学会の論文