Understanding Trout for Game Fishing: Salmo trutta

Salmo trutta is the native British brown trout. Almost everyone knows what a trout looks like, but almost no one could give you a definition that was worth much. Trout are one of the most plastic races of fish known. They can adapt themselves to all sorts of streams and lakes; they will live in fresh water or in the sea; they adapt readily to a great many countries, and are a favourite species for stocking wherever fish are needed to provide both sport and food.

Like all fish, trout reflect the quantity and quality of the food they eat. A quick-growing trout fed on large amounts of small nutritious organisms has a small head, beautiful proportions, and delicate colouration. A slow-growing trout, half-starved, which has augmented its diet by cannibalism, is a lanky ugly creature .

Like all living things, trout react quickly to environment, and become conditioned to the water in which they live. There are strains of trout living in water with a plentiful food supply which are adapted to assimilate nourishment quickly and in quantity. On the other hand, trout from poor waters are usually slow-growing even when introduced to richer pastures. Yet both are the same species.


Although scientists consider that there is only one British trout, Salmo trutta, there are a great many local forms and varieties. Many waters have their own distinctive forms of trout, spotting, colouration, and even shape varying with the locality. In one part of a remote Welsh river there is a race of red-eyed trout.

Trout colouration tends to be darker when the water is acid, lighter when the water is alkaline. More will be said about this later. Spotting, its frequency and pattern, seems to be due to variable biological factors. Trout are seldom, if ever, spotted exactly alike.

Among quick-growing trout may be cited the famous Loch Leven strain which feed on very rich pastures. Other quick-growing trout are cultivated by various midland reservoir authorities, and by those in Somerset.

Quick-growing trout are also found in rivers with rich feed such as the Usk. These fish, when contained in the new Usk reservoir, made good use of the feed and numbers grew to 1-1.5 kg (2-3 lb) with rapidity.

The chemical composition of water and its biological effect on living things is not our present concern, but the relative acidity of water is so fundamental to trout fishing that it may not be ignored. Rain-water, when it falls through unpolluted atmosphere is, for all practical purposes, neutral. Once it touches the earth this is no longer the case. Most water percolates through the top-soil and absorbs various chemicals and gases in its passage. It flows through and over rocks. By the time it reaches river or lake it has quite changed its character.

The best trout water is alkaline and is usually found in regions where limestone is a common rock-formation. Poor trout water is acid. Trout, of themselves, are largely indifferent to the acidity factor except when water changes rapidly as during a thunderstorm, but the small organisms which make trout tat are very dependent on the chemical state of the water. Snail, for example, is an important item of trout diet, and without lime in the water snails will not flourish.

Moorland streams are usually acid or, at best, neutral, but not always. Sometimes they flow over limestone bars, and these vastly improve the touting. Lakes and streams fed from springs rising in chalk strata provide some of our best trout fishing.

Trout would soon starve if they relied on floating duns for a living, and even in the most prolific waters they feed on a wide variety of fare. In limestone lakes the snail is a substantial and fattening item, which the trout swallow shell and all. In moorland streams the natural equivalent of the snail is the caddis or sedge larva in its case. Trout stuff themselves with the cases until their stomachs are distended.

The freshwater shrimp, water-fleas, and nymphs are other sources of nourishment. Bigger trout, however, need larger items of nourishment; sticklebacks in lakes, and minnows in rough streams are a common prey.

Flies are really a sort of dessert after the main dish, for only rarely can a trout gorge itself on flies and consider that it has had a square meal. For this reason, trout rise freely only during a substantial fly hatch. Otherwise, they are busy foraging elsewhere.

Before we can practise wet-fly fishing successfully it is important to have a clear idea of how trout typically react to their environment at different seasons. The temperature and condition of the water is of fundamental importance to such behaviour.

Let us consider a well-grown trout through twelve months, starting with winter. The water is cold — probably never more than 3-4°C (35-40°F) if spring-fed. Our fish has spawned and it is weak and ill-favoured. In these conditions the trout is in a state of semi-hibernation. Trout do feed in winter but the feeding is irregular and not part of a pattern. In any case, aquatic food-forms are at a minimum.

Early spring sees little increase in water-temperature; indeed, it may fall. But the lengthening day has its effect on weed-growth and the small animals that are nourished thereby. Some early flies will hatch, especially the hardy Large Dark Olive. Therefore the nymphs of this fly will have been active for some days past and trout will feed on them especially during the middle part of the day, as well as on the hatched dun.

Much of our fish’s early feeding therefore will be done deep down in the deepest and quietest pools. Bright sunshine may tempt the trout into the tails of the deeper runs for short periods, especially if the winter has been mild. But this will be only during the warmest part of the day.

Late spring sees the water a few degrees warmer, unless there are days of bitter north-east wind, which are only too common. More flies hatch and nymphal activity increases sharply. Our trout will now be feeding freely whenever a hatch occurs, but especially during the hours from about 11am to 3pm.

Early summer sees this trend even more strongly marked. Feeding will now be almost continuous during daylight hours. Intense sunshine, however, coupled with low water, will drive the trout to cover because it dislikes concentrations of ultra-violet on its skin. Although a trout enjoys the warmth it seems to sunburn easily.

Full summer sees an end to the day-fly hatches. Some, such us the BWO, seem to hatch all summer through, but these are not enough to sustain our lusty trout, which is now in prime condition. He quickly switches his attention to the minnow and to elvers if elvers run his river in quantity. Sedges and moths provide substantial fare during the short summer nights. Indeed, during the hottest weather he will do most of his feeding at night.

The approach of autumn sees a shortening of the day although the weather is often the best of the year for both trout and angler. Late-season hatches of day-flies begin and the trout takes a renewed interest in duns and spinners. He is now a fat fish and can be very choosey over the items of fare that float, crawl, or swim across his field of vision. Despite the nearness of the spawning season he can still give a good account of himself should he be silly enough to rise to a cleverly cast dun or to a sedge drawn over his lie at dusk.

In October he passes out of the angler’s ken — a protected fish once more. His function during the coming weeks will be to find a mate, take part in the reproductive process, and then sink into a state of dreamless lethargy until the boisterous winds of March herald another spring.

This thumb-nail sketch of a trout’s year is necessary so that we don’t waste time over fishing methods that are unlikely to be productive. If fish are absorbed in feeding on nymphs at the bottom of 1.8 m (6 ft) pools it is clearly a waste of time to draw wet flies through the surface film. Conversely, if they are feeding on minnow, they are not likely to bother with the angler’s nymph, solitary and tiny, fishing across the bottom.

Three-quarters of the problem of catching fish of any species is to diagnose correctly what they are feeding on at a given time. In trout fishing the other quarter of the problem is to show them similar fare in fly-form in an appropriate way.

In all game fishing we must remember the critical water-temperature of 13°C (50°F). Loosely speaking, water below 13°C (50°F) is ‘cold’ and water above this temperature is `warm’. Trout tend to feed down in cold water and up in warm water. Cold water slows up a fish’s metabolic processes so that it needs less food; warm water speeds them up and makes the fish hungry. There is of course an upper limit — about 24° (75°F) — above which trout suffer discomfort and refuse to feed at all.

The temperature of the air in relation to that of the water also important. A cool air-stream rapidly draws heat from water and fish dislike entering this cooling strata. An air-stream warmer than the water, however, quickly warms the upp strata and fish will rise into it freely. Although fish do hug the bottom when the water is cold they will nevertheless rise to surface fly if the air-stream is relatively warm.

It is always useful to check the air and water temperature. Some anglers use a thermometer; others use the backs of their hands.

19. July 2011 by admin
Categories: Fish, Game Fishing, Trout | Tags: , , | Comments Off on Understanding Trout for Game Fishing: Salmo trutta


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