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Author: Linnaeus, 1758

Salmo trutta Linnaeus, 1758

Diagnosis: elongate, becoming deeper with age, caudal peduncle deep, the fish not easily grasped by it. Tip of upper jaw reaching beyond hind margin of eye; lower jaw becomes curved in older males. A staggered line of teeth on shaft of vomer and 2-6 on head of vomer. Gillrakers 13-18. Dorsal finrays iii 8-11, and an adipose fin behind it; pelvic finrays i 8, base below latter half of dorsal fin; anal finrays ii-iii 8-9; caudal fin shallowly forked. Scales small, 118-130 in lateral line, 13-16 obliquely from adipose fin to lateral line. Vertebrae 56-61. Colour: variable, back green/brown, flanks silvery, belly white; black spots on back, on flanks above and below lateral line, and on head, also red spots with light edges; colour in sea more silvery than in freshwaters. Size: to 140 cm in migratory form, or 40 cm in freshwater forms.

Habitat: adults of marine form (sea trout) in inshore waters, often making considerable migrations (300 km not uncommon, over 600 km recorded), juveniles in estuaries; freshwater forms (brown trout, lake trout) in rivers, streams and lakes. Food: crustaceans and small fishes (herring, sprat, sand-eels, smelt); juveniles in freshwater take aquatic larvae of insects and later (as parr) eat winged adult insects, the adult brown trout feeding also on small fishes and crustaceans. Reproduction: spawning runs of sea trout in spring, summer or autumn, but mainly September/October to late January, the adults ascending far upstream and spawning from October to January at 3-4 years of age. Females dig and shape a 'nest' or redd in the gravel bottom, eggs and sperm are ejected simultaneously and the redd covered; spent adults return to the sea. Juveniles remain in streams and rivers as parr for 2-5 years before descending to the sea, where they spend 1-4 years (longer in north than in south). Brown and lake trout remain in freshwater.

Distribution: Atlantic coasts of Europe, from Barents Sea, northern Norway and Baltic southward to North Africa, also off southern Iceland; Black Sea, Sea of Azov, also Caspian and Aral Sea. Freshwater forms in rivers and lakes through area, occasionally straying into Mediterranean.

Subspecies

The following subspecific names are commonly used in the literature:
(marine, anadromous)

Salmo trutta trutta (Sea trout): 13-18 (usually 14-16) gillrakers, and 15-17 scales in oblique row from adipose fin to lateral line; Atlantic coasts; Clofnam 45.1.2.1.
Eggs, larvae and young stages. Winnicki, 1967: 50, pl. 2.
Otoliths (sagitta). Scott, 1906: 76, pl. IIB (fig. 30) | Shepherd, 1914: 109 | Frost, 1925: 157, pl. XII (fig. 45) | Tyslova, 1927: 1, fig. 17 | Sanz Echeverría, 1928: 162, pl. IV (fig. 10), pl. V (fig. 1) | Chaine, 1942: 127, pl. V | Bauzá-Rullán, 1962: 6, pl. 1 (fig. 3-8).

Salmo trutta labrax (Black Sea trout): 18-19 (usually 18) gillrakers, anc. 18-19 scales in oblique row from adipose fin to lateral line; Black Sea, Sea of Azov; Clofnam 45.1.2.2.
Eggs, larvae and young stages. No data.
Otoliths (sagitta). No data.

(freshwater)

Salmo trutta fario (Brown trout). Salmo trutta lacustris (Lake trout).

Sea or brown trout (Salmo trutta)