Amago salmon

Its range

This is the southern declension of the species, in the Japanese part of the range where it reaches its low-latitude limit. The rivers concerned are mountain rivers with clear, cold, well-oxygenated water, which reduces the distribution to a string of basins separated from one another by lowlands too warm to cross.

Fragmentation by climate rather than by relief is the fact that governs the conservation of the form. Each basin holds a population isolated from its neighbours, with no freshwater route between them, and warming of the lower reaches does nothing but push those boundaries further up the hill.

Identifying it

Red spots along the flank are what separate this fish from everything else in its species. They sit among the dark parr marks and, unlike them, persist into the adult instead of fading with growth; a Japanese salmonid carrying them has few other identities available.

Everything else — the slim outline, the black speckling, the flank marks — repeats the pattern of the mainland form, to which this trout attaches as a subspecies under the name Oncorhynchus masou ishikawae. The measurements displayed above belong to the binomial. No series of measurements has been taken on this form specifically, and the figures come from data gathered under the species as a whole.

Other names

Amago is the Japanese name for the fish that stays in the river, and English has taken it unchanged; red-spotted masu salmon is the descriptive alternative. The sea-run form carries a different name again, satsukimasu, built on the fifth month of the old calendar, which is when it comes back. Naming life forms rather than species is the Japanese habit throughout this group, and it is why one animal answers to several words over a life. German has Amago-Lachs.