Salmon are members of the family Salmonidae, a group of ray-finned fish known for their remarkable migrations between fresh and saltwater environments. This life cycle, known as anadromy, means they hatch in freshwater, travel to the ocean to mature, and return to their natal streams to reproduce. Classification focuses on the main, globally recognized species to provide a clear answer regarding the number of types.
The Primary Biological Classification
The fundamental division in salmon classification is based on their genus, splitting them into two major evolutionary lineages. All salmon species fall under the genera Salmo or Oncorhynchus, reflecting their geographic origin in the North Atlantic or North Pacific basins. The genus Salmo contains the single species known as the Atlantic salmon (Salmo salar), native to both the European and North American sides of the Atlantic Ocean.
The genus Oncorhynchus contains multiple species, collectively known as Pacific salmon. This biological separation dictates a major difference in their life histories. Atlantic salmon are iteroparous, meaning they can spawn multiple times over their lifespan.
Pacific salmon are semelparous; the adult fish die shortly after their single spawning event. This biological difference is a defining characteristic of the two groups.
The Five Major Pacific Species
The diversity of the Pacific Ocean is reflected in the existence of five primary species of North American salmon that are commercially and ecologically significant. The Chinook salmon, also known as King salmon, is the largest species, distinguished by its black mouth and spots across both lobes of its tail. Chinook are prized for their high oil content and rich, buttery flesh.
Sockeye salmon, or Red salmon, are known for their intensely red-colored flesh, which results from a diet rich in zooplankton and krill containing the pigment astaxanthin. They are one of two Pacific species that lack spots on their backs or tails, and they typically spawn in river systems connected to lakes. Coho salmon, often called Silver salmon, have a dark mouth with white gums, and their spots are generally limited to the upper lobe of the tail.
Pink salmon, nicknamed Humpback or Humpies, are the smallest and most numerous of the Pacific species. They are identifiable by large, oval spots on their back and tail, and males develop a prominent hump upon returning to freshwater. Finally, the Chum salmon, sometimes called Keta or Dog salmon, is the other species with an unspotted back and tail, recognized for having a white mouth and gum-line.
Key Differences in Size and Habitat
Size provides the most immediate comparison among the Pacific species, with Chinook salmon reaching the largest maximum size, sometimes weighing over 100 pounds. Conversely, Pink salmon are smaller, averaging between three and five pounds, making them the most diminutive of the group.
Habitat use during the spawning migration also varies significantly among the species. Pink and Chum salmon generally spawn in streams closer to the ocean, sometimes only traveling short distances upstream from the coast. Chinook and Coho salmon are known for their ability to undertake massive migrations, sometimes journeying more than a thousand kilometers inland to their natal spawning grounds. Sockeye salmon exhibit a distinct habitat requirement, as their juveniles require a lake environment for at least one year before migrating to the sea.