THE ANIMAL FILES

Common roach

Rutilus rutilus

A silvery shoaling fish changes its menu as it grows.

The common roach is a silvery freshwater fish whose fins and eyes can carry red colour. Young fish are relatively slender; older ones often grow deeper-bodied. Its use of vegetation links shelter, feeding and development.[1]

Follow the evidence ↓
Common roach
Image: Scardinius_erythropthalmus1_resize.jpg: Original uploader was Algirdas at lt.wikipedia derivative work: George Chernilevsky talk · Commons · CC BY-SA 3.0
Social life
Shoaling[1]
Young fish
Plankton is an important food[1]
Adult diet
Plants and aquatic invertebrates[1]

Colour is not the only clue

Roach can resemble rudd, dace and ide. Eye and fin colour may be pale in some environments, while mouth position, fin placement and scale details add distinctions. A red fin alone is not a complete identification.[1]

Vegetation has two jobs

Plants shelter larvae and young fish, while mature roach can also eat plant material. Adults take bottom-living invertebrates and other foods, broadening the plankton-based diet of smaller fish.[1]

Season changes the water column used

Roach tend to use deeper water during cold periods and feed nearer the surface in warmer conditions. Rising spring and summer water temperatures also help trigger spawning, connecting movement and reproduction to seasonal water conditions.[1]

A COMMON MIX-UP

Does every red-finned fish belong to this species?

No. Similar fishes share colours, and roach colour itself varies. Several structural features are needed for a careful comparison.[1]

TRY A LITTLE REASONING

Why might removing plants affect young and adult roach differently?

Reveal the explanation

Young fish lose protective cover, while adults can also lose a source of plant food. The same habitat feature serves different roles.[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 — Common roach (fixed revision; adapted and translated)
  2. NCBI Taxonomy — Rutilus rutilus (identity and classification)

Last fact check:

One discovery leads to another

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