Marble trout (Salmo marmoratus), characterized by distinctive marbled color pattern and high growth capacity, is native to the North Adriatic river systems, (e.g. the Po river system in Italy and the Soča/Isonzo river system in Slovenia and Italy). Phenotypically similar trout have been described also in some rivers of the western Balkans flowing into the Adriatic Sea. Northern populations of marble trout (from Italy and Slovenia) are associated with one of five brown trout evolutionary lineages (i.e., marmoratus lineage characterized by several “Ma haplotypes”) inferred from mitochondrial DNA (mtDNA) control region sequences (see Bernatchez et al., 1992; Bernatchez, 2001 or Snoj et al., 2000, for details about trout evolutionary lineages). However, recent studies have shown that phenotypically marbled trout from the rivers Neretva (Croatia, Bosnia-Herzegovina) and Zeta (Montenegro) bear other haplotypes than Ma indicating that the marbled color pattern and Ma haplotypes may not be directly related. On the other hand, brown trout (Salmo trutta) from several locations across central Mediterranean (Albania, West Greece, Corsica and central Italy) were found to exhibit previously mentioned Ma haplotypes. Interestingly, even a Scandinavian population of brown trout from the River Otra in Norway (Skaala & Solberg, 1997) were found to bear marbled color pattern, although genetic markers and other phenotypic characters of these trout do not resemble to those characteristic of the Adriatic marble trout (Delling, 2002).
Several records of marble trout translocation out of its natural range have been reported in the past. For instance, according to unverified information, in Slovenia marble trout have been translocated into many rivers outside its native range in order to increase the size of native brown trout. And indeed, using molecular genetic analysis, we observed genetic traces of marble trout in the Danubian part of the river system in Slovenia (Jug et al., 2005) and confirmed rumors about marble trout translocations.
Marble trout is one of the most endangered freshwater species. The main threat to marble trout has been hybridization with introduced brown trout. The first recorded stocking in the Soča basin was performed in 1906 using brown trout from Bosnia. Contrary to the popular believe of critical devastation of marble trout during the WWl, marble trout was still abundant in Soča after the war (Gridelli, 1936; Razpet et al., 2007), however the stocking with brown trout, presumably originating from the Atlantic river basin, continued and reached its peak in the time of Yugoslavia. In late eighties of the previous century, non native brown trout of the Atlantic origin and its hybrids with the native marble trout dominated almost the entire Adriatic part of Slovenian river system (Povž et al., 1996), with the exception of eight small populations found in the following decade in some remote and isolated reaches of the very upper part of the Soča and Idrijca drainages (Berrebi et al., 2000; Fumagalli et al., 2002
In a close collaboration of Dr. Meta Povž from Fisheries Research Institute of Slovenia, French researchers Dr. Alain Crivelli and Dr. Patrick Berrebi and Dušan Jesenšek, the manager of Tolmin fish farm of the Angling Club of Tolmin, an action plan for marble trout restoration was initiated in 1992 and later joint also by the Department of Animal Science at the University of Ljubljana. The main idea was to create genitor stocks based on the eight genetically pure populations of marble trout, and use their progeny for stocking the Soča basin in order to eventually replace brown trout non-native genes with the marble trout ones and slowly regain the situation characteristic of the Soča basin before brown trout introduction. Simultaneously, brown trout stocking has been ceased making rehabilitation of marble trout a realistic goal in the next decades (Povž et al., 1996; Berrebi et al., 2000; Crivelli et al., 2000).
In order to efficiently monitor the progress of the action plan and to be able to identify genetically pure individuals from zones, where marble and introduced brown trout co-exist, the next goal has been to develop several new molecular markers enabling differentiation between marble trout, brown trout and the hybrids. In the mean time, phylogenetically oriented studies have been conducted in order to reveal genealogy, colonization patterns and relationship of different marble trout population across its entire native range including the populations from Bosnia-Herzegovina and Montenegro (see also the River Neretva, rivers of Montenegro).
Bernatchez L., Guyomard R. & Bonhomme F. 1992. Molecular Ecology 1: 161-173.
Bernatchez L. 2001. Evolution, 55, 2: 351-379.
Berrebi P., Povž M., Jesenšek D., Cattaneo-Berrebi G., Crivelli A.J. 2000. Heredity, 85: 277-287.
Crivelli, A., Poizat, G., Berrebi, P., Jesenšek, P., Rubin, J. F. 2000. Cybium 24: 211–230.
Delling, B., 2002. Cybium 24 (4): 283-300.
Fumagalli, L., Snoj, A., Jesenšek, D., Balloux, F., Jug, T., Duron, O., Brossier, F., Crivelli, A.J. 2002. Molecular Ecology 11 (12): 2711-2716.
Gridelli, E., 1936. Bollettino della Societa Adriatica di Scienze Naturali in Trieste 34: 7-140.
Jug, T, Berrebi, P, Snoj, A. 2005. Biological Conservation 123, p. 381-388.
Povž, M., Jesenšek, D., Berrebi, P., Crivelli, A. 1996. The marble trout, Salmo trutta marmoratus, Cuvier 1817 in the Soča river basin, Slovenia. Arles, Station de biologique de la Tour du Valat publication.
Razpet, A., Marić, S., Parapot, T., Nikolić, V., Simonović, P. 2007. Italian Journal of Zoology, 74: 63-70.
Skaala, O., Solberg. G. 1997. Nordic Journal of Freshwater Research 73: 5-15.
Snoj A., Jug T., Melkič E., Sušnik S., Pohar J., Dovč P. & Budihna N. 2000. Journal of Freshwater Biology (Quaderni ETP) 29: 5-11.