Marble trout (Salmo marmoratus)

Is a freshwater fish that lives in the Soča River and its tributaries, and is also widespread in the Adriatic basin. The smaller ones stay in medium-deep water, while the larger ones stay in deep pools and are solitary. Marble trout is an endemic fish of the Adriatic basin and belongs to the set of Slovenian indigenous species.

Part of the Latin name marmoratus refers to the distinctive marbled pattern on the back and head. It can be recognized by its elongated cylindrical body between 50 and 70 centimeters long and its marbled pattern on a gray-white background. The pattern can be dark gray, brown, olive green, copper red, or yellow brown. There may be more or less red dots or freckles among the marble pattern. It can reach a weight of over 20 kg. Until now, the longest caught in Slovenia measured 121 cm and weighed 25 kg.

Adult animals feed on fish and hunt in the dark, while juveniles mainly feed on ground food, plankton and insects. They spawn from November to January on the gravel riverbed.

More than fishing itself, they are threatened by genetic mixing with introduced brown trout. For the past ten years, fishermen and fishing families have been working hard to make most of the trout in Soča once again autochthonous by raising genetic clean populations and catching brown trout.

Brown trout (Salmo trutta)

Is a freshwater fish of the Danube basin and is the most numerous and widespread native trout species in Europe. In addition to the Danube, it can also be found in other river basins where it was widely introduced globally as a game fish, even becoming one of the world’s worst invasive species outside of its native range. In adition, due to the successful crossbreeding with marble trout, the purebred marble trout was endangered. Younger fish feed mainly on ground food and various insects, while larger trout are primarily piscivorous.

In our country, it grows from 20 to 80 cm, but exceptionally it can be up to 1 m long and weigh more than 13 kg. Their backs are olive-dark brown and silver-blue, red spots with a light edge appear up to the belly, the belly itself is whitish yellow. In sexually mature males, the lower jaw is hooked upwards. In our country, brown trout spawn from mid-December to the end of January.

Its interesting feature is loyalty to its area, which is especially evident when it lacks rain for a long time and the riverbed turns golden brown. This coloration is not present on the stands of watercress, because it is prevented by the continuous movement of the tail. Otherwise, the habitat of the brook trout is a few tens of meters of the river or stream.

Rainbow trout (Oncorhynchus mykiss)

Is a species of trout that originally lived only in the Pacific Ocean and in the lakes of North America west of the Rocky Mountains. Today, rainbow trout are found all over the world and are highly prized as food, but in some places they have seriously affected native animal species.

Rainbow trout are on average 30 to 40 cm long, but in our country they grow up to 80 cm. Exceptionally, they also live in the sea, where they grow from 50 to 100 cm and weigh between 2.5 and 10 kg. Their special feature is that although they spend their entire lives in fresh water, they can also migrate to the sea under the right conditions, but they must return to fresh water to mate.

It entered our rivers through breeding in fish farms for edible fish, mainly as an input to diversify fishing. Although at first it did not reproduce in rivers, it soon adapted to the local conditions here, began to reproduce and inhabit areas of rivers and streams where it had never been introduced. Although it does not interbreed with the native Soča trout, it is a competitive and aggressive competitor for food, space and success on the spawning grounds.

When it comes to feeding, the rainbow trout is typically not picky, it takes every available food, and it is also active for most of the day, which makes it a very common catch. Even smaller rainbows can stage an interesting fight with various jumps from the water and strong shaking of the head.

Grayling (Thymallus thymallus)

Is a freshwater fish of the trout family, although it is a rather uncharacteristic fish for trout. It is widespread in England, southern Scandinavia, in the rivers that flow into the North Sea, in the upper tributaries of the Volga and throughout most of Europe. In our country, it can be found in the upper reaches of almost all rivers, in recent decades it has disappeared only from the Mura.

The grayling has a strongly flattened body and a convex back with a distinctive, iridescent, long and high dorsal fin. Graylings have a small head with a small overhanging mouth that has soft lips. The body is orange-silver or gray in color and is covered with fairly large scales that are arranged in straight rows. The Adriatic grayling is characteristic of the Soča basin, which differs from the Grayling from the Sava basin by its grayer color and the absence of black spots on the front part of the body.

On average graylings grow between 25 and 35 cm, but in exceptional cases they can reach up to 60 cm and 7 kg. It is an extremely interesting fish for sport fishing, especially for fly fishing, and wherever fishing is allowed, it is protected by a fishing permit, minimum catch rate, fishing method and a limited number of fish caught.

They feed mainly on aquatic insects, but also various ground invertebrates and eggs other fish. However, their elegant and unique picking of insects from the surface of the water is  the most characteristic. After reaching sexual maturity in their third or fourth year of age, they spawn in March and April on the gravel bottom.

One of the main reasons for the fairly stable grayling population is the massive return of hatchery-raised fingerlings back into the rivers. In its natural environment, it is most threatened by the presence of the cormorant, from which the grayling cannot hide, as well as pollution and regulation of watercourses.

In the Soča Valley, rich ecosystems encompass not only the most commonly described types of trout and hybrids but also other fascinating fish species. Although less frequently encountered, they occupy important ecological niches and are inherently beautiful and interesting. Among such species are the barbel (Barbus plebejus), Chub (Leuciscus cephalus cabeda), Editerranean barbel (Barbus meridionalis caninus), Friuli chub (Leuciscus souffia muticellus), Minnow (Phoxinus phoxinus phoxinus), Bullhead (Cottus gobio), and Friuli bleak (Alburnus a. Alborella). Occasionally and only in specific sections, we may also spot Tench (Tinca tinca), Roach (Rutilus rubilio aula), and Rudd (Scardinius erythrophthalmus erythrophthalmus).