Order:	Salmoniformes
Family:	Salmonidae
Genus and species:	Salmo trutta

William Yarrell (1836) in "A History of British Fishes":

THE COMMON TROUT.

Salmo	fario,	Linnæus.
"	"	River-Trout,
Penn. Brit. Zool. vol. iii. p. 399, pl. 70.
"	"	Trout,
Don. Brit. Fish. pl. 85.
"	"	Common Trout,
Flem. Brit. An. p. 181, sp. 47.

THE COMMON TROUT is too widely diffused and too generally known to make any enumeration of particular localities necessary: it is an inhabitant of most of the rivers and lakes of Great Britain, and so closely identified with the pursuits and gratifications of sportsmen, that those landed proprietors who possess streams of water favourable to the production and growth of Trout preserve them with great care and at considerable expense. The Trout, though a voracious feeder, and thus affording excellent diversion to the experienced angler, is so vigilant, cautious, and active, that great skill as well as patience are required to ensure success. During the day, the larger sized fish move but little from their accustomed haunts ; but towards evening and during the night they rove in search of small fish, insects, and their various larvæ, upon which they feed with eagerness. The young Trout fry may be seen throughout the day sporting on the shallow gravelly scours of the stream, where the want of sufficient depth of water, or the greater caution of larger and older fish, prevent their appearance.
Though vigilant and cautious in the extreme, the Trout is also bold and active. A Pike and a Trout put into a confined place together had several battles for a particular spot, but the Trout was eventually the master.
The season of spawning with the Trout is generally in the month of October, at which period the adult fish make their way up the stream ; and the under jaw of the old male exhibits in a smaller degree the elongation and curvature observed to obtain in the male Salmon, of which an instance will be shown.
The Trout varies considerably in appearance in different localities ; so much so, as to have induced the belief that several species exist. It is, indeed, probable that more than one species of river Trout may exist in this country ; but when we consider geologically the various strata traversed by rivers in their course, the effect these variations of soil must produce upon the water, and the influence which the constant operation of the water is likely to produce upon the fish that inhabit it ; - when we reflect also on the great variety and quality of the food afforded by different rivers, depending also on soil and situation, and the additional effect which these combined causes in their various degrees are likely to produce; - we shall not be much surprised at the variations both in size and colour which are found to occur. That two Trout of very different appearance and quality should be found within a limited locality in the same lake or river, is not so easily explained ; and close examination of the various parts which afford the most permanent characters should be resorted to, with a view to determine whether the subject ought to be considered only as a variety, or entitled to rank as a species. In these examinations the character of the internal organs also, and the number of the bones forming the vertebral column, should be ascertained. The normal number of vertebræ in Salmo fario, our Common Trout, I believe to be fifty-six.
Sir William Jardine, Bart. in a paper on the Salmonidæ, published in the Edinburgh New Philosophical Journal for January 1835, has described at considerable length the variations observed in the Trout of some of the lochs of Sutherlandshire. Other lochs abound with Trout which are reddish, dark, or silvery, according, to the clearness of the water. Mr. Neill, in his Tour, has noticed the blackmoss Trout of Loch Knitching, and Loch Katrine is said to abound also with small black Trout ; an effect considered to be produced in some waters by receiving the drainings of boggy moors. In streams that flow rapidly over gravelly or rocky bottoms, the Trout are generally remarkable for the brilliancy and beauty of their spots and colours. Trout are finest in appearance and flavour from the end of May till towards the end of September ; an effect produced by the greater quantity and variety of nutritious food obtained during that period. Two specimens of the Common Trout taken early in January were unusually fine in colour for that season of the year ; their stomachs on examination were distended with ova of large size, which, from circumstances attending the capture of the Trout, were known to be the roe of the Bull-Trout. The albuminous nature of this sort of food, which the Trout availed themselves of, was believed to be the cause of their colour ; since other Trout, procured at the same time from localities where no such food could be obtained, were of the usual dark colour of that season of the year.
Mr. Stoddart, in his "Art of Angling as practised in Scotland," mentions an interesting experiment made with Trout, some years ago in the south of England, in order to ascertain the value of different food. Fish were placed in three separate tanks, one of which was supplied daily with worms, another with live minnows, and the third with those small dark-coloured water-flies which are to be found moving about on the surface under banks and sheltered places. The Trout fed with worms grew slowly, and had a lean appearance ; those nourished on minnows, which, it was observed, they darted at with great voracity, became much larger ; while such as were fattened upon flies only, attained in a short time prodigious dimensions, weighing twice as much as both the others together, although the quantity of food swallowed by them was in nowise so great."
Of four Trout fed in a stew together, three of them weighed fifteen pounds each, the fourth attained the weight of seventeen pounds ; but neither the food nor the time consumed was recorded.
Stephen Oliver the younger, in his agreeable Scenes and Recollections of Fly-fishing, mentions a Trout "taken in the neighbourhood of Great Driffield, in September 1832, which measured thirty-one inches in length, twenty-one in girth, and weighed seventeen pounds." A few years since, a notice was sent to the Linnean Society of a Trout that was caught on the 11 th of January 1822, in a little stream, ten feet wide, branching from the Avon, at the back of Castlestreet, Salisbury. On being taken out of the water, its weight was found to be twenty-five pounds. Mrs. Powell, at the bottom of whose garden the fish was first discovered, placed it in a pond, where it was fed and lived four months, but had decreased in weight at the time of its death to twenty-one pounds and a quarter.
The age to which Trout may arrive has not been ascertained. Mr. Oliver mentions, that in August 1809, "a Trout died which had been for twenty-eight years an inhabitant of the well at Dumbarton Castle. It had never increased in size from the time of its being put in, when it weighed about a pound ; and had become so tame, that it would receive its food from the hands of the soldiers." In August 1826, the Westmoreland Advertiser contained a paragraph stating that a Trout had lived fifty-three years in a well in the orchard of Mr. William Mossop, of Board Hall, near Broughton-in-Furness.
The Thames at various places produces Trout of very large size. Among the best localities may be named Kingston, opposite the public-house called the Angler, Hampton-Court bridge and wear, and the wears at Shepperton and Chertsey. These large Trout are objects of great attraction to some of the best London anglers, who unite a degree of skill and patience rarely to be exceeded. The most usual mode practised to deceive these experienced fish is by trolling or spinning with a small Bleak, Gudgeon, or Minnow ; and Trout of fifteen pounds' weight are occasionally taken.
On the 21st of March in the present year, 1835, a male Trout of fifteen pounds' weight was caught in a net. The length of this fish was thirty inches. On the 14th of April following, a male Trout of eleven pounds' weight, and measuring twenty-eight inches in length, was also caught in a net. From this second fish the representation here shown was taken, by permission of Mr. Groves, who allowed a drawing to be made, which was engraved for this work.

Some deep pools in the Thames above Oxford afford excellent Trout, and some of them of very large size. I have before me a record of six, taken by minnow spinning, which weighed together fifty-four pounds, the largest of them thirteen pounds. Few persons are aware of the difficulty of taking a Trout when it has attained twelve or fourteen pounds' weight, and it is very seldom that one of this size is hooked and landed except by a first-rate fisherman : such a fish, when in good condition, is considered a present worthy a place at a royal table.
Among performances in Trout catching, the following may be mentioned, as found in the MS. of the late Colonel Montagu.
"Mr. Popham, of Littlecot, in the county of Wilts, was famous for a Trout fishery. They were confined to a certain portion of a river by grating, so that fish of a moderate size could not escape. To the preserving and fattening these fish much trouble and expense were devoted, and fish of seven and eight pounds' weight were not uncommon. A gentleman at Lackham, in the same county, had a favourite water-spaniel that was condemned to suffer death for killing all the Carp in his master's ponds, but was reprieved at the desire of Mr. Popham, who took charge of him, in the belief that so shy and so swift a fish as a Trout was not to be caught by a dog. However, in this he was mistaken, for the dog soon convinced him that his largest Trout were not a match for him." Mr. Stoddart also, in his Scottish Angling, Page 119, has recorded the sities of a fish-catching dog.
I am indebted to William Thompson, Esq. of Belfast, for a very fine specimen of the Gillaroo Trout of Lough Neagh, measuring twenty-two inches in length, from which fish the representation on this page was taken. The internal surface of the stomach presented an indurated cuticle, but the parietes were not thicker than those of other Trout; the cavity was filled with some dozens of the Palu-dina impura of Lamarck. The fin-rays and vertebrae were- --

D. 12 : P. 14 : V. 9 : A. 11. : C. 19. Vertebræ 56.

So little difference appeared to exist between this and English specimens of S. fario, as to induce the belief that the Gillaroo is only a variety of the Common Trout, as stated by Pennant.
Several loughs in Ireland produce this fish, which sometimes attains the weight of ten or twelve pounds. The teeth are remarkably small, but in number and situation like those of S. fario.
The figure of the Trout at the head of this article, and the following description, were taken from a Hampshire fish of twelve inches in length.
The length of the head compared to the length of the head and body, not including, the caudal rays, was as one to four ; the depth of the body rather more than the length of the head : the dorsal fin commenced half-way between the point of the nose and the commencement of the upper caudal rays ; the third ray of the dorsal fin, which is the longest, longer than the base of the fin : the origin of the adipose fin half-way between the commencement of the dorsal fin and the end of the upper half of the tail ; the pectoral fin two-thirds of the length of the head; the ventral fins under the middle of the dorsal fin, and half-way between the origin of the pectoral fin and the end of the base of the anal fin ; the anal fin begins half-way between the origin of the ventral fin and the commencement of the inferior caudal rays. The tail but slightly forked, and growing slowly up to square in old fish, or even very slightly convex, as seen in the figure of the large Thames Trout. The fin-rays in number are --

D. 14 : P. 14 : V. 9 : A. 11 : C. 19. Vertebræ 56.

The form of the head blunt ; the eye large, placed one diameter and a half from the end of the nose ; the irides silvery, with a tinge of pink: the lower jaw in the Salmonidæ appears to be the longest when the mouth is opened, but it shuts within the upper jaw when the mouth is closed ; the teeth numerous, strong, and curving inwards, extending along the whole length of the vomer ; the disposition of the teeth and the form of the gill-cover shown in outline at page 3 ; the convexity of the dorsal and ventral outline nearly similar: the colour of the back and upper part of the sides made up of numerous dark reddish brown spots on a yellow brown ground ; eleven or twelve bright red spots along the lateral line, with a few other red spots above and below the line ; the lower part of the sides golden yellow ; belly and under surface silvery white ; the spots on the sides liable to great variation in number, size, and colour ; dorsal fin and tail light brown, with numerous darker brown spots ; the adipose fin brown, frequently with one or two darker brown spots, and edged with red ; the pectoral, ventral, and anal fins uniform pale orange brown. The number of scales in a row above and underneath the lateral line about twenty-five.
Deformed Trout are not uncommon ; mention of them as occurring in some of the lakes of Wales is made by Pennant, Oliver, and Hansard. "In 1829," says the writer of the article on Angling in the seventh edition of the Encyclopædia Britanniica, "we received some very singular Trouts from a small loch called Lochdow, near Pitmain, in Inveriness-shire. Their heads were short and round, and their upper jaws were truncated, like that of a bull-dog. They do not occur in any of the neighbouring lochs, and have not been observed beyond the weight of half a pound." Such a Trout from Lochdow was presented to the Museum of the Zoological Society by the Honourable Twiselton Fiennes : the vignette is a representation of the head of that specimen.

Alwyne Wheeler (1969) in "The Fishes of the British Isles and North West Europe":

Trout [Brown Trout, Sea Trout]

Salmo trutta Linnaeus, 1758

NAMES Fr. Truite; Du. Forel; Ge. Forelle; Da. Ørred; Nor. Örret. (Many local names.)
The following subspecific names have been and still are occasionally used for the types of trout:
Brown Trout -- Salmo trutta fario L.; Sea Trout -- Salmo trutta trutta L.; Lake Trout --Salmo trutta lacustris L.

IDENTIFICATION The trout is extremely variable in colour and not a little so in body shape, depending on its surroundings and habits. Small dark fish, usually living in the smaller rivers and pools, are mostly known as brown trout and are non-migratory; larger paler specimens in large waters are called bull trout or lake trout and may be migratory, while the large silvery sea trout is distinctly migratory. All are variants of the single species.
Trout can be distinguished by the long upper jaw-bone reaching well past the hind edge of the eye. In older males the lower jaw becomes hooked. The caudal peduncle is deep, and the tail fin is at the most shallowly forked. Scales relatively small, between thirteen and sixteen from the adipose fin to the lateral line, and from 120 to 130 in the lateral line. There are teeth on the vomerine bone (in the centre of the palate), two to six on the head of the vomer, up to eighteen on the shaft (Fig. 56B), although the number is reduced with age.
D. 12-14; A. 10-12; vertebrae 56-61.
Colour very variable; greenish brown on the back, the sides lighter, and the belly yellowish. There are black and red spots on the flanks, the latter light ringed; spots are always present on the gill covers; the adipose fin is orange tinted. Sea trout are grey or silvery with black and reddish spots which are always present on the gill cover.
In small waters the trout grows to 16 in (41 cm); the migratory form grows to 55 in (140 cm).

BIOLOGY Trout typically inhabit the cleaner, well-oxygenated waters of the upper reaches of rivers and lakes. They are, however, found also in lowland reaches where the water is turbid, warmer and, except at the surface, not well oxygenated. Trout breed in winter, from October to January, sometimes to February, usually in temperatures of 5-10°C (41-50°F). Sexual maturity occurs in males at two years, in females at three years of age. Spawning always occurs on gravelly shallows, in which the female cuts a redd by means of flexions of the tail. The eggs are shed and are fertilised immediately by the male, which stations himself beside but slightly behind the female. The eggs are buried by the female in later redd digging, and hatch in about forty days at a temperature of 10°C (50°F). The fry (alevins) hatch at a length of ½-1 in (15-25 mm), and the yolk sac is absorbed in four to six weeks, after which they commence feeding. A general downstream migration follows hatching.
Growth varies remarkably with locality and with temperature, fish in alpine streams being smaller on average than those from broad lowland rivers; trout which descend to the sea are larger still. In small streams the growth rate is relatively slow, an average of 2½ in (6 cm) at the end of the first year, 5 in (13 cm) at the second and 8 in (20 cm) at the end of the third year. Sea trout, having migrated as smolts at an average length of 8½ in (21 cm), grow faster, adding 3-5 in (7.5-13 cm) in their first sea year, 4-5 in (10-13 cm) in their second, and may measure 19 in (48 cm) after their third sea year. The size distribution of sea trout is as variable from river to river as is that of the purely freshwater forms.
The food of young trout is almost identical to that of young salmon. Trout fry eat the aquatic stages of Ephemeroptera, Coleoptera and chironomids, but rarely eat the adults of these insects. The parr, however, eat considerable quantities of the winged insects, particularly in midsummer, when they are entering their adult stage. The parr also eat the nymphs of both Ephemeroptera and Plecoptera, larvae of coleoptera, and larvae and pupae of chironomids. In addition, parr and adolescent trout eat a wide range of miscellaneous aquatic and terrestrial animals which fall into the water. Adult brown trout feed on fishes, crustaceans (particularly Gammarus), aquatic insect larvae, and adult winged insects. The food of the sea trout has been relatively little studied, but in general the range of animals eaten is large. It is mainly composed of fishes, particularly the sprat, young herring and sand eels (Ammodytes tobianus and A. lanceolatus), but crustaceans form a large proportion of the diet. They include the amphipods Corophium and gammarids generally, decapods, such as the brown shrimp and prawn, and mysid shrimps. Feeding in estuaries is heavy and many of the food organisms are estuarine in origin; there is evidence that some sea trout penetrate into almost fresh water and feed there, presumably as a result of tidal movements.
Sea trout make extensive migrations in the sea. Journeys of two hundred miles are not uncommon, and some four hundred miles and more are on record. Speed of travel is fairly low, apparent speeds of up to eight and a half miles a day having been recorded.
Trout in general are highly favoured angling fish. Brown trout are much sought after, and are taken in many ways, chiefly by fly fishing. Sea trout are equally regarded and on account of their greater size (of up to 30 lb (13.5 kg)) are somewhat more valuable. The British record brown trout weighed 17 lb 12 oz (7.75 kg). Trout possess a considerable commercial value, both for their angling and fishery value and for food.

DISTRIBUTION

Migratory form mostly on western coasts, south to Biscay, and in certain European lakes. South to N. Africa.