Marine and fresh-water Fishes, mostly from the temperate and Arctic zones of the northern hemisphere: one genus (Retropinna) on the coasts and in the rivers of New Zealand; a few deep-sea forms (Argentina, Microstoma, Nansenia, Bathylagus) occur in the Arctic Ocean, the North Atlantic Ocean, the Mediterranean, and the Antarctic Ocean, down to 2000 fathoms. Apparently of comparatively recent age, no remains older than Miocene (Osmerus, Thaumaturus, Prothymallus) being certainly referable to this family. The recent genera may be grouped as follows:—
A. Air-bladder present.
a. Branchiostegal rays 8 to 20; ventral rays 9 to 13; stomach siphonal; pyloric appendages more or less numerous (17 to 200). Breed in fresh water. Salmo, Brachymystax, Stenodus, Coregonus, Phylogephyra, Thymallus.
b. Branchiostegal rays 6; ventral rays 11 to 14; stomach caecal; pyloric appendages in moderate numbers (12 to 20). Argentina.
c. Branchiostegal rays 6 to 10; ventral rays 6 to 8; stomach caecal; pyloric appendages few (2 to 11) or rather numerous. Osmerus, Thaleichthys, Mallotus, Plecoglossus, Hypomesus.
d. Branchiostegal rays 3 or 4; ventral rays 8 to 10; stomach caecal; pyloric appendages absent. Microstoma, Nansenia, Bathylagus.
B. Air-bladder absent; branchiostegal rays 3 to 6; ventral rays 6 or 7; stomach siphonal; pyloric appendages absent. Retropinna, Salanx.
Only about 80 species can, at present, be regarded as valid.
Fig. 342.—Distribution of Salmonidae (deep-sea forms not included).