THE ANIMAL FILES

Atlantic cod

Gadus morhua

A shoal shares a journey, not necessarily an identical meal.

Atlantic cod combine group movement with diets that vary as individuals grow.[1]

Follow the evidence ↓
Atlantic cod
Image: Wilhelm Thomas Fiege · Commons · CC BY-SA 4.0
Moving in a shoal
Group structure can reflect size[1]
A growing menu
Small cod and large cod differ[1]
Activity has a timetable
Swimming varies with time of day[1]

Moving in a shoal

Cod form size-structured aggregations. In one migration study, larger fish near the front obtained more varied food than smaller trailing fish. This does not establish a universal leader for every shoal.[1]

A growing menu

Stomach-content studies find small cod relying more on crustaceans and larger cod taking more fish. Local prey also matter.[1]

Activity has a timetable

One set of swimming observations recorded greater daytime activity. Seasonal day length may also affect activity patterns; these findings do not establish a fixed timetable for every population.[1]

A COMMON MIX-UP

Does every cod in a shoal necessarily have the same diet?

No. Size and position can relate to feeding differences in the studies described. Group membership does not erase individual variation.[1]

TRY A LITTLE REASONING

Why compare stomach samples from similar-sized fish?

Reveal the explanation

Diet changes with growth. Without accounting for size, a difference between samples might reflect different developmental stages rather than only a change in available prey.[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 — Atlantic cod (cited revision)
  2. NCBI Taxonomy — Gadus morhua

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