Salmonidae

4.14 | Salmonidae View in CoL View at ENA

The diversity of Caucasian trouts is very poorly understood, what is related to the very recent evolutionary history of all species. Actually, trouts of the northern Caspian Caucasus are identified as S. ciscaucasicus , described from the Keyranchay River. Those of the southern Caucasus are identified as S. caspius , described from the Kura in Azerbaijan. Ninua, Tarkhnishvili, and Gvazava, (2018) support this view and suggest using S. caspius for trouts from the rivers flowing into the Caspian Sea south of the Caucasus and S. ciscaucasicus for that found in the Terek River and other rivers flowing into the Caspian north of the Caucasus. This system might be oversimplified and more research will for sure challenge our understanding of the species diversity of Caspian trouts. The Black Sea trouts were usually identified as S. labrax until Turan, Kottelat, and Engin (2009) showed that within the Coruh River drainage, two forms coexist, which they named S. rizeensis and S. coruhensis , the former purely riverine and the latter anadromous. Ninua et al. (2018) suggested that the mitochondrial haplogroup of S. rizeensis was never found in fish caught in the Black Sea. Ninua et al. (2018) support S. rizeensis and S. coruhensis as own species different from S. labrax but indicate some hybridisation between S. coruhensis and S. labrax in the Georgian Caucasus, a situation expected to happen in two anadromous, migratory species at their distribution border area.

The trouts of the Salmo ischchan complex are endemic to Lake Sevan (Armenia). Four “forms” of Sevan trouts are generally recognised ( S. ischchan , S. gegarkuni , S. danilewskii and S. aestivalis ) ( Barach, 1940; Dadikyan, 1986; Gabrielyan, 2001; Levin, Simonov, Rastorguev, et al., 2018; Pipoyan, 2012). These have been interpreted as subspecies, ecological forms or life-history types. The available evidence strongly suggests that they had been species following the Evolutionary Species Concept (see Kottelat, 1997 for definitions). The four trout species were very closely related and might have been the result of sympatric speciation events happening after the last glacial times (<10,000 years ago). While Sevan trout diversity has been poorly studied, this very interesting example of intra-lacustrine trout speciation has already been lost. The abundance of all Sevan trouts drastically declined in the twentieth century due to overfishing and loss of spawning grounds due to water diversion and a critical 18.5-m drop of the lake water level finally leading to the extinction of two of the endemic species. S. ischchan and S. danilewskii are considered to be extinct since the 1980-ies ( Levin & Rubenyan, 2010; Pipoyan, 2012). The two other species, S. gegarkuni and S. aestivalis are believed to still exist but they are largely or completely dependent on artificial reproduction and stocking.