Marble trout can be found in several countries across the Adriatic basin. In Italy, they inhabit left tributaries of the upper northwestern reaches of the Po River, as well as the direct Adriatic watersheds of the Adige, Brenta, Piave, Tagliamento, and Livenza rivers. Slovenia shares the Soča and Natisone drainage with Italy, where marble trout can also be found. Additionally, marble trout are found in the Neretva river basin in Bosnia and Herzegovina and Croatia, as well as in the Morača and Zeta rivers in Montenegro and Albania. While once present in the Drin river basin in Albania, the fish is considered most likely extirpated there. Similarly, the species is also believed to be extirpated from the Aoos river basin in Albania and Greece.
Marble trout possess a distinct marbled color pattern that sets them apart from other fish species. They have a long, cylindrical body that is slightly compressed laterally, with a relatively large head comprising approximately 22-25% of the body length. This unique characteristic has led to their alternative name, "glavatica," which means "head" in Bosnian.
The intensity of the marble pattern varies, depending on the trout's surroundings. Some marble trout even exhibit red spots along the lateral line, blending seamlessly with the rest of their pigmentation. With an average size ranging from 30 to 70 cm, these fish can grow significantly larger. The largest recorded specimen in Slovenia was a female measuring 117 cm in length and weighing 24 kg. Reports of individuals weighing up to 30 kg have also been documented. Marble trout typically reach sexual maturity at 3+ years for males and 4+ years for females, spawning during November and December.
Marble trout are piscivorous, primarily feeding on smaller fish and benthic invertebrates. They thrive in rivers with a summer temperature of around 15 °C (59 °F). However, despite their remarkable adaptability, marble trout face numerous threats to their existence throughout their range.
One of the significant challenges for marble trout conservation is hybridization with foreign trout species that have been introduced for angling purposes. This hybridization poses risks to the genetic integrity of the pure marble trout populations. Water extraction, pollution, and habitat loss due to dam construction also contribute to their declining numbers. In particular, Bosnia and Herzegovina faces threats such as habitat destruction from the construction of large dams on the Neretva River and plans for additional dams on its upper course. Overfishing, including both legal and illegal practices, further exacerbates the situation.
Despite the challenges, conservation efforts have been underway to protect the remaining genetically pure marble trout populations. Currently, all eight known genetically pure populations are found in remote streams within the River Soča basin. The Tolmin Angler's Society in Slovenia has taken the initiative to launch a reintroduction program aimed at