三陸地方南部の河川におけるサクラマスの降海型と河川残留型の卵巣発達

概要

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Masu salmon were collected from a river in the southern Sanriku district (Pacific side of Northern Honshu) where two forms of female, fluviatile and sea-run forms, are recognized. The observation of the ovarian development of these fish revealed that the females can be sepa-rated into two groups after the second November from being spawned. One is the group whose gonad weights (GW) increase rapidly. The other is the group whose GW remain un-changed from November to the following April. The distribution of oocyte diameter of the first group is bimodal and the large oocytes show gradual development from the late peri-nucleolus stage to oil drop stages. The distribution of oocyte diameter of the second group is unimodal, and only the late peri-nucleolus stage is seen in most of their ovaries throughout the period from August to the following April. Based on successive observations of body shape and coloration until the second spring, all the fish with the first group ovary are found to become stream resident parr (fluviatile form), while most fish with the second group ovary become smolt (sea-run form), while the rest stay as small parr.
公益社団法人日本水産学会の論文