THE ANIMAL FILES

Atlantic salmon

Salmo salar

The same fish changes its water and its appearance.

Atlantic salmon connect freshwater development with, in many populations, a period of ocean feeding and a return to rivers. Yet landlocked populations also exist. Their changing color and life stages make this an example of a broad pattern with important exceptions, not one compulsory journey for every fish.[1]

Follow the evidence ↓
Atlantic salmon
Image: Hartley, William W. · Commons · Public domain
Migration
Many populations move between rivers and sea[1]
Early nutrition
Newly hatched young use a yolk sac[1]
Spawning site
A gravel-bed depression called a redd[1]

A river beginning

Early young draw on remaining yolk before becoming active feeders. Later freshwater stages differ in appearance and behavior, including the marked parr stage. Naming these stages helps explain why two salmon of the same species can look unlike each other. Development is not simply a small fish becoming larger without other changes.[1]

Preparing for a different water

Many fish transform into smolts before moving toward salt water, where a major period of feeding and growth can occur. This is a developmental transition as well as a change of location. The existence of fully freshwater populations is an important qualification: the species description must leave room for more than one life-history route.[1]

Gravel is part of reproduction

A female moves gravel with tail-generated water flow to form a spawning depression and later cover deposited eggs. Some Atlantic salmon survive spawning and can reproduce again, though repeat spawning is not universal. Following the fish after egg laying therefore matters as much as observing its return to the river.[1]

A COMMON MIX-UP

Must every Atlantic salmon visit the sea?

No. The source records landlocked populations that complete their life cycle in freshwater. Common patterns should not erase documented exceptions.[1]

TRY A LITTLE REASONING

Why is color alone a risky way to separate young and adult salmon into species?

Reveal the explanation

Color changes with development and reproductive stage. Identity needs to be checked across life stages rather than assuming one permanent appearance.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — Salmo salar (adapted and translated; exact revision)
  2. NCBI Taxonomy — Salmo salar (identity and game lineage)

Last fact check:

One discovery leads to another

Brown troutRiver, lake or sea: different journeys can belong to one species.Salmo trutta ↗Rainbow troutA river resident and a sea traveller can share one species name.Oncorhynchus mykiss ↗Northern pikeA still fish can be preparing a very sudden movement.Esox lucius ↗