The Coho or Silver Salmon (Oncorhynchus kisutch) has black spots on the back and upper lobe of the caudal fin. The gums are light at the base of the teeth. At sea, these salmon are metallic blue above and silver below. Breeding males have dusky green on the back and head, with bright red sides and a black belly; females have bonze to pink-red sides. Spawning males develop a strongly hooked snout and large teeth. Maximum length is around 100 cm. Chinook Salmon (O. tshawytscha) are very similar in appearance to Coho Salmon while at sea, but Chinook Salmon are larger, have black spots on both the upper and lower caudal fin lobes, and have gums that are dark at the base of the teeth. (Page and Burr 1991)
Coho Salmon occur in northeastern Asia and, in North America, in Arctic and Pacific drainages from Point Hope, Alaska, to Monterey Bay, California (occasionally as far south as Baja California). These fish are anadromous, returning from the ocean to the coastal streams or rivers where they were born to spawn. They reproduce just once, then die. (Page and Burr 1991)
For detailed information on the biology and status of this species, including conservation issues, see this resource from the NOAA Fisheries Office of Protected Resources.