Marble Trout: Endangered Fish Species in Balkan Rivers

Marble Trout:

Endangered Fish Species in Balkan Rivers

The Marble trout (Salmo marmoratus) is endemic to the Adriatic basin and can reach 120cm and 25 kilos in size, making it a much sought-after trophy fish on a fly rod. It owes its name to the distinctive marbled color pattern, which is reminiscent of that in many char species – for instance brook trout.

BY THE EDITORIAL STAFF // PHOTOS BY RASMUS OVESEN and UROS KRISTIAN

In the Balkans, the marble trout occurs in the Soča basin in Slovenia (and Italy) (also the Rižana and Reka rivers), in the Neretva basin in Bosnia-Herzegovina, and the Skadar basin in Montenegro (Zeta, Morača and Cijevna rivers), where the species is now becoming increasingly rare.

Marble trout become sexually mature at the age of 3+ years (males) and 4+ years (females), and they spawn in November and December. They are believed to grow to at least 15 years, and the bigger specimens are voracious predators that feed on grayling, sculpins, and other trout – mostly at night or when the rivers rise and the water, subsequently, becomes turbid.

Although mainly found in mountainous regions, where deep pockets, pools below waterfalls, and big boulders provide shelter, marble trout can also be found in adjoined lakes and reservoirs, where they hunt pelagically.

Because brown trout were introduced in the region, and because it hybridizes with the marble tout, pure populations have become very rare. In fact, outside of the Balkans there are no genetically pure populations left. The last pure populations in Slovenia are found in a few very small and isolated tributaries of the Idrijca (Soča basin).

Hybridization, however, is not the only threat to the marble trout: the species is highly sensitive to dam construction. Hydropower expansion on the upper Cijevna River (Cemi River) in Albania, the Morača River in Montenegro, and the Neretva River in Bosnia-Herzegovina, as well as the Soča basin in Slovenia pose a threat to at least 50% if not 75% of the species range in the Balkans.

The “Save the Blue Heart of Europe” campaign is dedicated to save the Balkan rivers from destruction by 3500 dam projects. Find out more here: www.balkanrivers.net

Interested in other endangered fish? Check out this online database of endangered fish species in the Balkans: https://balkanrivers.net/en/fish-database

Sources: Balkan Rivers – Endangered Fish Species: Distribution and threats from hydropower development: https://bit.ly/3d4iP4V

To zoom into the distribution area, check out the Fish Study layer in this interactive map: https://balkanrivers.net/en/map