The question of whether trout and salmon are related often arises due to their similar appearances and shared habitats. While distinct, these popular fish share a significant biological connection, leading to common characteristics and notable differences. This article explores their scientific classification, shared traits, and unique life histories to clarify this relationship.
Their Place in the Fish Family Tree
Trout and salmon both belong to the scientific family Salmonidae, which encompasses a wide range of cold-water fish found predominantly in the Northern Hemisphere. This family also includes char, freshwater whitefish, and grayling. Within Salmonidae, species are further categorized into different genera. The primary genera containing fish commonly referred to as “salmon” or “trout” are Oncorhynchus, Salmo, and Salvelinus.
The genus Oncorhynchus includes all Pacific salmon species, such as Chinook, coho, and sockeye, alongside several Pacific trout species like the rainbow trout and cutthroat trout. This shared genus explains why some “trout” (like steelhead, anadromous rainbow trout) are often confused with salmon. Conversely, Atlantic salmon belong to the genus Salmo, which also includes brown trout. The genus Salvelinus comprises char, such as brook trout and lake trout.
Similarities Between Trout and Salmon
Many shared characteristics contribute to the frequent confusion between trout and salmon. Both fish possess streamlined bodies. They also feature an adipose fin, a small, fleshy fin located between the dorsal and caudal (tail) fins, which is a distinguishing trait of the Salmonidae family. Their general body shape and fin structures exhibit a strong resemblance.
These species also prefer similar aquatic environments. They thrive in cold, clear, and oxygen-rich freshwater, such as rivers, streams, and lakes. Many species of both trout and salmon also exhibit anadromy, a life history where they are born in freshwater, migrate to the ocean to mature, and then return to freshwater to spawn. Their spawning behavior is notably similar, as females of both groups construct nests, called redds, in gravel beds in freshwater to lay their eggs, which are then fertilized by males.
Key Differences Between Trout and Salmon
Despite their similarities, trout and salmon exhibit several distinctions in their physical characteristics and life cycles. Salmon are larger and have a more robust body shape than trout, which are smaller and more slender. Salmon display a more silvery, metallic hue in their ocean phase, while trout have more varied coloration with distinct spots scattered across their bodies and fins. Their tails also differ; many salmon species have a noticeably forked tail, whereas many trout species possess a squarer or less forked tail. Their jaw structure also varies; the upper jaw of adult salmon reaches no further than the rear of the eye, while in trout, it extends beyond the eye.
Their life cycles also differ. While both groups can be anadromous, many trout populations remain entirely in freshwater throughout their lives, a lifestyle known as resident. In contrast, most salmon species are obligately anadromous, undertaking migrations between freshwater and saltwater. A distinction lies in their spawning frequency: many Pacific salmon species are semelparous, meaning they spawn once and then die shortly after. Conversely, most trout species are iteroparous, capable of spawning multiple times over their lifespan, returning to spawn in successive years.