Salmon are awe-inspiring fish that swim the oceans before traveling upriver to spawn. Salmon are also delicious, and are a popular fish purchased in supermarkets and restaurants. Whether you are a budding field biologist or a fisherman, you should be able to tell the differences between male and female salmon.

While living in the ocean, male and female salmon have very subtle differences. Careful examination may find small variations in jaw shape and head size, but generally they can only be told apart when they're cut open after they have been caught. However, when salmon begin to spawn, the male goes through several changes. After this, males and females can be more easily differentiated.

Male salmon have a larger head-to-body ratio than female salmon. This becomes more noticeable late in the year when they are spawning. The male salmon's head grows even larger and will appear more elongated than the female salmon's head.

The male salmon always has longer jaws than the female, and there is a hook shape to the male jaws. When the time to spawn approaches, the male jaws become much more exaggerated. The male salmon's jaws grow even longer and develop a more pronounced hook. He also develops strong, sharp teeth at this time, while the female's teeth are more modest.

In the ocean, male and female salmon are both silver in color. However, as spawning time arrives, the male salmon typically displays brighter color changes; the female salmon's color is more subdued. Male sockeye salmon turn a bright red, while the female turns more green than red. Male salmon in the Baltic Sea turn deep colors of yellow and brown with mixed shades of red, while the female remains mostly silver with black and purple coloration. Male chum salmon develop more pronounced color patterns than the females as well.

The body shape of the male and female salmon in the ocean is very similar. Once they have returned to the rivers to spawn, subtle changes occur to their body shapes. The male's body becomes deeper, with slender sides. The female has a more slender body, but her belly will become rounded with eggs.

In Pacific salmon, the male has a more pronounced adipose fin. The fin located on the male's back, nearest his tail, will be two to three times bigger than that of the female.