During their ocean phase, Coho have silver sides and dark blue backs. During their spawning phase, the jaws and teeth of the coho become hooked. They develop bright red sides, bluish green heads and backs, dark bellies and dark spots on their backs. Sexually maturing coho develop a light pink or rose shading along the belly and the males may show a slight arching of the back. Mature adults have a pronounced red skin color with darker backs and average 28 inches (71 cm) and 7 to 11 pounds (3.2 to 5.0 kg) occasionally reaching 36 pounds (16 kg). Mature females may be darker than males, with both showing a pronounced hook on the nose.
http://en.wikipedia.org/wiki/Coho_salmon
