〇 Salmon physiology: Seawater adaptation

Faculty of Fisheries Sciences, Hokkaido University　SHIMIZU Munetaka

Most salmonids are born in freshwater and spend a certain period in rivers before descending to the sea. However, the descent characteristics (age, duration, etc.) differ among species. Even within the same species, there are cases where some individuals descend to the sea and others remain in the river depending on the river environment. Genetic factors are also important. In other words, salmonid oceanic descent is influenced by the interaction of genetic and environmental factors. In this lecture, the seemingly simple phenomenon of salmonid descent to the sea will be explained from various perspectives. Specifically, topics such as why they descend to the sea, how they adapt from freshwater to seawater, and to what extent their descent to the sea is genetic will be covered.

Polymorphism in the life history of cherry salmon in Hokkaido, Japan

Why, how, and how many down the river?

体サイズ: body size 冬: winter 春: spring 夏: summer 秋: autumn 1年目: first year 2年目: second year

相分化成熟のため川に残る雄（早熟雄）: males that remain in the river for phasic maturation (precocious males) 海へ下る個体（スモルト）: individuals descending to the sea (smolt) 幼魚として川に残る個体（パー）: individuals remaining in the river as juveniles (parr)