What you're looking at
The brown trout (Salmo trutta) is the UK's iconic native salmonid, a hugely variable fish that ranges from finger-sized brook trout in upland becks to giant deep-water ferox in Highland lochs. The same species as the sea trout; "brown trout" simply refers to the river/lake life form that doesn't migrate to sea.
Key features
- Body: Streamlined, muscular, classic salmonid shape with an adipose fin (small fleshy fin between dorsal and tail).
- Markings: Olive-bronze back, golden-buttery flanks. Heavily peppered with black spots and red spots haloed in pale rings. Spots extend onto the gill cover.
- Tail: Square or slightly concave, with very few spots above the lateral line on the wrist, a separator from immature salmon.
- Fins: Adipose fin often orange-tipped. Anal fin shorter than its base length.
- Size: Stream fish 0.1–0.4 kg; river/lake fish to 1–2 kg; reservoir fish often stocked at 1.5–3 kg; wild ferox of Scottish lochs to over 10 kg.
Confusion species
- Sea trout: Same species; recognised by silver flanks, deeper body, fewer red spots, often fresh sea lice. Found in rivers with sea access during summer/autumn.
- Salmon parr (juvenile): Strong "parr marks" (vertical bars), few/no red spots, deeply forked tail, fewer spots on the gill cover. Often released by mistake, check before keeping.
- Rainbow trout: Pink/purple lateral stripe, black spots only (no red), heavily spotted tail.
Where to find them
Clean, cool, oxygenated water, chalk streams, freestone rivers, upland lakes and stocked reservoirs. River browns hold in lies that offer shelter and a feed conveyor: behind boulders, under trees, on the edge of fast water meeting slow. The trout season opens in April in most of England and Wales; sea-trout-bearing rivers have separate dates.