Salmon are fish known for their remarkable life cycles and diverse appearances. While sharing fundamental characteristics, their visual traits vary significantly depending on the species and life stage. Understanding these differences provides insight into their biology and adaptations.
General Appearance
Most salmon in their ocean-going phase exhibit a streamlined, torpedo-shaped body for efficient movement through water. Their coloration features a silvery body with a darker back, aiding camouflage in the open ocean. A distinguishing characteristic of salmon is the adipose fin, a small, fleshy fin located on the back between the dorsal fin and the large, forked tail. Salmon possess relatively small scales and vary widely in size, with some species averaging a few pounds and others growing to over 30 pounds.
Differences Among Species
Salmon species display distinct appearances when in the ocean or freshwater migration.
Chinook salmon, often called King salmon, are the largest Pacific salmon. They have a blue-green back with silvery sides, featuring irregular black spots on their back and both lobes of their tail fin. Their black gum line is a key identifier, known as “blackmouth”.
Sockeye salmon, also known as Red salmon or Blueback salmon, are smaller. They are recognized by their iridescent silver flanks, white belly, and metallic green-blue top, lacking large spots on their body or fins.
Coho salmon, or Silver salmon, have dark metallic blue or greenish backs with silver sides and a light belly, with small black spots on their back and the upper lobe of their tail. Unlike Chinook, Coho salmon have a lighter, often white, gumline.
Pink salmon, the smallest and most abundant Pacific salmon, are characterized by large, dark oval spots on their back and entire tail fin. In the ocean, they are steel blue to blue-green on the back with silver sides.
Chum salmon, also called Dog or Keta salmon, are metallic greenish-blue on the back with black speckles but lack distinct black spots on their body or fins. Their mouth often appears pale.
Atlantic salmon, distinct from Pacific species, have a long, thin body and are silvery with scattered black spots, often X-shaped, above their lateral line, but usually not on their caudal fin.
Appearance Changes During Life
A salmon’s appearance undergoes transformations throughout its life cycle, especially during its migration from freshwater to the ocean and back to freshwater for spawning. Juvenile salmon, known as parr, live in freshwater and have distinctive vertical markings called parr marks on their sides, which provide camouflage in river environments. These marks fade as they transition into smolts, developing a silvery coloration that helps them blend into the open ocean.
Upon returning to freshwater for spawning, adult salmon undergo changes in color and body shape. Their silvery ocean coloration gives way to hues, such as the red bodies and green heads of Sockeye salmon, or the reddish-maroon sides of Coho salmon. Male salmon of many species develop a hooked jaw, called a kype, and some, like Pink salmon, grow a hump on their back, contributing to their “humpback” nickname. These changes in appearance are linked to sexual maturity and the spawning migration.
Identifying Salmon
Identifying salmon involves observing a combination of their physical features, which change with species and life stage. A consistent characteristic across all salmon species is the adipose fin.
When attempting to identify a specific salmon, consider its overall body shape, the presence and pattern of spots on its back and tail, and the coloration of its gums. For instance, the black gum line of a Chinook salmon is a reliable distinguishing feature, while the absence of large spots often points to a Sockeye. Observing multiple characteristics, rather than relying on a single one, provides the most accurate identification of these diverse and adaptable fish.