Home Fishes The trout’s anatomy and senses

The trout’s anatomy and senses

  • Trout are powerful and athletic fish, able to thrive in fast flowing or still-waters.
  • Trout can live in vigorous water currents flowing at speeds of up to 24.14km (15 miles) per hours.
  • Trout are streamlined for action.
  • The trout’s body from gills to tail is power-packed muscle.
  • Trout have supreme eye-body-fin coordination.
  • The trout’s mouth is lined with tiny inward-pointing sharp teeth, so prey once seized, can’t escape.
  • Trout are perfect predators.
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Anatomy of the Trout

All members of the salmon (Salmonidae) family can be distinguished by the presence of the fatty, small adipose fin on the back, between dorsal fin and caudal fin (tail).

The dorsal and anal fins enable the trout to balance. The pectoral and pelvic fins assist movement. The caudal fin (tail), combined with body movement, propels the trout through water.

The air bladder controls air pressure inside the trout, empowering the trout to rise or sink in water and maintain the desired depth.

The lateral line is a series of tiny holes (pores), giving the appearance of a line. The pores communicate changes in pressure to the trouts brain, supplying a special sense of feeling.

An adult trout can swim at 8.05km (5 miles) per hour for hours, reach a comfortable sprint speed of 16.09km (10 miles) per hour, and accelerate to a speed of 24.14km (15 miles) per hour in short bursts.

A hooked trout, racing from an angler for its life, can touch 32.18km (20 miles) per hour.

A wary feeding trout snatches food fast and jets to safety.

A hooked trout’s rapid acceleration puts a huge strain on an angler’s line. The trout’s sudden explosion of energy can break strong line.

An accelerating trout weighing 227g (1/2 lb) can snap fishing line tested to 1.1kg (2 1/2lb) breaking strain.

The trout’s Senses

The trout has highly developed senses of sight, hearing, feeling, smell and taste.


Trout have binocular (focusing with both eyes) vision of what lies before them – to pinpoint prey – and independent monocular (one eye only) vision of 180 degrees on each side.

In clear water, trout can see objects up to 4.57km (12 feet) away, and discern different colors; in murky water and at night, trout switch to black and white vision.

Trout have, in effect, all round color and black and white vision.

The trout’s eyes are sensitive to bright light. (Fish have no eyelids to protect their eyes from bright light.) Trout prefer to avoid bright light by diving deep or swimming into shaded areas of water.

The Trout’s Vision

Trout’s eyes are slow to adjust to rapid changes in light and trout can have trouble focusing when day dawns, suddenly brightens or darkens, or when dusk falls quickly.

At times of rapid change in light trout may be slow to see us and we have an advantage over them.

Be aware that a calm water surface acts as a mirror for trout. When the water is calm, trout can see an angler’s above water movements, monitor water surface insect activity, and simultaneously view images of below water natural food and the movement of anglers’ artificial imitations: images mirrored downward from the surface of calm water.

The trout’s are of surface vision is affected by the trout’s depth in the water. A trout lying 127mm (5 inches) beneath the surface may only see natural prey present, or an artificial fly presented by the angler, in a surface area 127mm (5 inches) across.

This area of vision, called the trout’s surface window, increases in correspondence with the trout’s depth beneath the water surface: a trout lying 305mm (12 inches) beneath the surface, will have a surface window vision of about 305mm (12 inches) across.

The trout’s perception of surface objects becomes dimmer and less distinct the deeper it lies beneath the water surface.

A trout intent on surface feeding may not immediately see a food item landing outside its surface window area of vision.

Accurate casting direct to surface feeding trout is very important.

Trout have well developed night vision, and, once their sight becomes accustomed to the dark, can locate food by sight.

Trout also employ their other senses.


The trout has two sensitive ears inside its head and can hear sound vibrations transmitted through water 12m (40 feet) from the sound’s source.

Sound travels 4 1/2 times faster through water (approximately 1 mile or 1.61km per second) than through air. Sound is also clearer in water than in air.

We must approach the waterside quietly, treading softly.


The trout’s lateral line of tiny pores along its sides feels underwater vibrations (pressure waves), alerting the trout to the presence of objects and minute movements in the water up to 7.62m (25 feet) distant.

Information passed to the trout’s brain from the lateral line enables the trout to identify the origin, position, size and speed of the source of the vibrations.

The lateral line helps the trout manoeuvre, detect the slightest change in temperature, and distinguish vibrations that alert the trout to the presences of careless anglers, natural predators, and potential prey.

A blind trout can rely on its lateral line to hunt prey, feed and navigate its way around the water. Blind trout turn black in color, although not all black-colored trout are blind.


Trout have a highly developed sense of smell, enabling them to identify minuscule traces of natural scent and track prey for long distances in murky water and at night.
A wary trout will not toy long with an artificial fly impregnated with the telltale smell of human manufacture, storage and handling.

We must be quick to tighten out line and drive the hook into the mouth of a trout investigating an artificial fly tied to our fishing line.


The trout’s mouth has sensitive taste buds. Trout are familiar with the normal feel and flavor of their favorite natural foods.

The unfamiliar taste and texture of an anglers artificial fly may lead to the artificial’s immediate rejection.

The presence of a metal hook will soon be detected and the artificial fly rejected.

When a trout intercepts and seizes out artificial fly, we have at best seconds to act before the trout realizes its mistake, ejects the fly and escapes.