Vol. 50 No. 3, 2011

Clutch and Egg Sizes of Two Migratory Forms of the Threespine Stickleback Gasterosteus aculeatus in Eastern Hokkaido, Japan

Manabu Kume

Laboratory of Breeding Science, Graduate School of Fisheries Sciences, Hokkaido Univ., 3-1-1, Minato-cho, Hakodate, Hokkaido 041- 8611, Japan

Manabu Kume (2011) Clutch and egg sizes were compared between the Japan Sea and Pacific Ocean forms of the threespine stickleback collected from the Bekanbeushi River in eastern Hokkaido, Japan. The Japan Sea form produced many small-sized eggs, whereas the Pacific Ocean form produced fewer large-sized eggs, suggesting the existence of a trade-off between clutch and egg sizes in both forms. A previous study revealed that the 2 forms diverged in their breeding habitats by using different salinity regimes within a single watershed. These findings suggest that the Japan Sea and Pacific Ocean forms have evolved different reproductive strategies and characteristics in response to differing salinities and properties of their respective environments.

Key words: Egg, Reproductive strategy, Salinity adaptation, Anadromy, Gasterosteus aculeatus.

*Correspondence: Tel: 81-586-896036. Fax: 81-586-896039. E-mail:m-kume77@pwri.go.jp