Brown Trout

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.