The fish species in Bohinj are determined by Lake Bohinj and the Sava Bohinjka. These two fairly different aquatic environments provide suitable living conditions for different species of fish. Some species are exclusively tied to running waters, others to the calm waters of the lake, while others live in both aquatic environments.
Until the introduction of the lake char, it was the dominant fish species of lake Bohinj. They reached weights up to 20 kg and grew up to 220 cm. There are still quite a few of them in the lake, but their number is also lower due to intensive fishing in the past. They are also threatened by the introduction of lake trout from other environments, even from lake Ohrid in Macedonia.
The lake trout is very similar to the brown trout in body shape. It differs from brown trout by its distinctly dotted back with black dots of various shapes. The abdomen area is light, the caudal fin is almost flat in adult fish, while it is incised in younger fish.
Lake trout prefer to stay in the depths at the outflows of torrential tributaries and ground springs (Ukanc at the mouth of the Savica, along the coast below Pršivec, in Fužinarski zaliv …), but we can observe them watching for prey very close to the shore. Lake trout is a very timid fish and we must approach it very carefully. Juveniles feed mainly on ground food, while adult trout are predators that feed mainly on fish.
They spawn in autumn – in October and November. The peak of spawning is in the second half of October, in November and in the first half of December. At favorable water levels of the tributaries, they come to spawning grounds in Savica, Mostnica and Ribnica. After spawning, they return to the depths of the lake. They rarely spawn in the lake itself (on the gravels of torrential tributaries Savica, Govic waterfall), but only at low water levels of tributaries.
The brown trout is a resident of lake Bohinj, Sava Bohinjka and its tributaries. The species that comes to spawn in the Savica are different in appearance from the brown trout from the Sava (their basic phenotypic characteristics). They are more stocky and have larger red spots that are metallic blue bordered. The body of the brown trout, which comes from the lake, is golden yellow along the lateral line, as if sprinkled with gold dust. Flesh is red because of the diet. It also grows up to 60 cm and more. The brown trout that lives in the Sava does not reach such a length, does not have such a beautiful golden yellow color along the lateral line and does not have such large red spots, nor as red flesh as the brown trout that lives in the lake. This indicates the possibility that in Bohinj, in addition to lake trout, there were different forms of brown trout, which did not interbreed due to the different place or time of spawning. There are quite a few such cases of coexistence of different forms of brown trout in Europe. Therefore, the results of genetic research, which is already being carried out on Bohinj brown trout, will be very interesting.
As in other waters in Slovenia, in the past, brown trout from other Danube and even Atlantic river basins were introduced in Bohinj waters. Therefore, it is difficult to find a real Bohinj brown trout in the Sava and most tributaries. These remained only in the upper stretches of some tributaries, such as Mostnica, Suha, Jereka and Ribnica.
The characteristic of these trout is that they live in very difficult conditions, as these are waters of torrential character in which there is less food. They adjusted their life habits accordingly. The body of these brown trout is more cylindrical in shape than the brown trout from the Sava. The caudal fin and the adipose fin are distinctly red on this brown trout, the flesh is tenderly red in color and sometimes almost yellow. Red spots are smaller and fairly densely scattered, mixing all over the body with black spots. These preserved remains of the original brown trout and trout that are coming to spawn in the Savica will be the basis for the repopulation of brown trout in Bohinj.
The brown trout feeds mainly on ground invertebrates, it also likes insects on the water surface; larger specimens of this species are fish eaters.
It spawns in late autumn and early winter; the peak of spawning is in November. The most important spawning grounds are in the tributaries of the Sava, in Mostnica, Ribnica, Belca, Bezdena and in Savica. It also spawns in the Sava. Due to the increased intake of gravel from the Sava riverbed, at lower water levels, the access of brown trout from the Sava to spawning grounds in tributaries is difficult, sometimes even impossible.
It inhabits the Sava river, parts of its tributaries and the lake. The most beautiful grayling district is the lower reaches of the Mostnica, which Bohinj anglers are especially proud of.
The grayling, which lives in the Sava Bohinjka, has a strongly flattened body, a bulging back and a characteristically high and long dorsal fin of beautiful rainbow colors that looks like a chessboard. The body is covered with relatively large scales. The grayling has no scales on its head. Its head is relatively small with slightly lower mouths that have soft lips. Grayling from the Sava prefers to stay in jets and overflows. These are also the easiest places for anglers to notice it, as it has beautifully fins, which are orange-red in color.
In the last decade, the grayling population has been decimated by cormorants, and grayling is also badly affected by the poorer water quality in the Sava and the increased exploitation of Sava gravel. Grayling feeds on ground invertebrates, but because it also likes to feed on insects on the surface of the water, it is very important for sport fishing – fly fishing. In Bohinj, grayling spawn in April and early May. Their spawning grounds are in the Sava, Mostnica and Ribnica rivers.
Artificial grayling breeding in Slovenia has also started in Bohinj. This one relied on fish from the Sava. The source of food for grayling fry was plankton from Lake Bohinj. Unfortunately, breeding has been abandoned in recent years and the fish farm below Pršivec is collapsing. The fishermen of Bohinj must thus start breeding grayling anew and preserve the tradition.
In Bohinj we can find a bunch of other indigenous fish species.
Burbot is a resident of the lake. In recent years, its catches in the lake have been declining. This may also be related to a change in the way the lake char is fished.
Chub inhabits the lake and the Sava. On the lake you can see whole shoals of chubs “sunbathing” below the surface. In the Sava, the number of chubs was reduced by the increased presence of huchen.
Huchen was only an occasional guest in the Sava. Today, due to intensive stocking, this species is numerous, which results in a decreased number of cyprinids in the Sava river.
Population of the souffia is stable both in the lake and in the Sava. The same is true for the dace population.
Bullhead is in decline in the Sava. The cause can be both the quality of the water and gravel exploitation. The population in the lake is good.
Minnow used to be the main bait for fishing lake char. Today, however, its population is declining due to the presence of perch that has appeared in the lake.
Especially in the tributaries of the Sava, mediterranean barbel are also found. Here we can also find stone crayfish.
Bohinj waters were not exempted from stocking with a non-native – allochthonous fish species.
The first was the lake char introduced in 1943. This species adapted to the conditions in the lake and began to spawn successfully. It has become the most common type of trout in lake Bohinj. Here it grows to a size of 70 cm and weighs 4.6 kg.
Lake char prefers to stay in the Fužina bay, in the depths along Pršivec and in Ukanc at the mouth of the Savica. They feed on lake plankton, ground organisms and smaller fish. They spawn in the lake in October and November. The largest spawning ground is below the Govic waterfall.
Regardless of the fact that the lake char is an alien fish, it is very important for sport fishing. Due to its culinary value, it must acquire a greater role in the culinary offer of Bohinj area in the future.
There is also a brook trout in the Sava. In the past, fishermen have stocked it heavily in fishing waters. Fry can also be seen, indicating that this species has started to reproduce successfully naturally.
Rainbow trout is being stocked in the Sava River. In recent years, we have only stocked sterile fish. Regardless of this, the rainbow trout is already successfully reproducing naturally in Bohinj.
The last newcomer is a perch. He came to the lake as bait for lake trout. The number of perch is growing rapidly. Because it is a successful predator, its impact is already seen on the minnow population, and other fish populations inhabiting the lake are also at risk.