Pre-Caucasian trout (Salmo trutta ciscaucasicus) - as a necessary component of the Caspian ichthyofauna

Caspian trout is an arctic immigrant, endemic, and is a subspecies of bull-trout that lives in the northern waters of the Russian Federation. There are three fish populations in the Caspian: Kura, Terek and Samur. Kura is the most numerous population, in contrast to Terek and Samur. [6] separated the Terek and Samur populations of bulltrout into a separate subspecies, calling it the Ciscaucasian bull-trout (Salmo trutta ciscaucasicus). Consequently, two subspecies of the northern and Kura bull-trout Salmo trutta currently live in the Caspian basin. The third subspecies, described by Berg, lives in the alpine lake Eisenam, with an area of 160 hectares (Lake Andean). The lake was formed as a result of a landslide, with a maximum depth of 75m. The lake is drainless and its isolation from the numerous inflows of the Sulak River is stable. As a result of landslides, there are a lot of cases of lake formation. In 1905. as a result of a landslide in the upper reaches of the Samur River at an altitude of about 2000 m above sea level, a lake was formed. Dzheneh, and the lake trout was a permanent inhabitant here, which was described by D.Z. Demin as Salmo trutta caspius Kessler morphalacustris. At the same time, it is important to consider the Ciscaucasian bulltrout, lake and river trout of Dagestan, as a unified reproduction fund of the Sulak River. Currently, the Samur population of Terek bull-trout is bred at the Primorsk Experimental Fish Hatchery, which has certain production capacities and about 50 thousand units of this fish juveniles with a piece weight of 3-5g were produced in 2020. It is impossible to catch breeders of the Ciscaucasian bull-trout in the required quantities, since this representative belongs to the first category of species in the Red Book of the Russian Federation - and the entire volume of reared and released larvae and juveniles comes from the factory broodstock.

Sulak is the second largest river in terms of water content, and there is no information in the historical literature on the visit and breeding of the Ciscaucasian bull-trout in this river, although brook and lake trout live in the upper reaches of all inflows and lakes in proportion to the feeding capacity of the reservoir, and here the obstruction in the middle reaches of the river can be explained. Hence, it follows that the stocks of the Ciscaucasian bull-trout in the Caspian decreased due to the lack of conditions for the migration of trout to the Caspian and contrariwise. Considering the Ciscaucasian trout, brook and lake trout, as a unified reproduction fund, there is no doubt that with the increase in the capacity of fish farms, it is necessary to intensify work on the commercial cultivation of trout with their subsequent release into the lower reaches of the Terek, Sulak, Samur rivers and other watercourses of the republic. Trout is considered to be plastic fish. There are known facts of transformation of brook trout, i.e. non-passable forms into anadromous form – bull-trout and vice versa.

The migration of the Caspian Ciscaucasian bull-trout in various rivers takes place within wide temperature ranges and covers a significant period of time. So, the course of the bull-trout in the river Terek usually started in autumn (September) and lasted all winter. There are summer, spring, autumn and winter races of bull-trout in the Caspian sea. Ciscaucasian bull-trout of Samur River is locally called "samurbalyk". Ciscaucasian bull-trout is a predatory fish and by increasing fish-breeding processes there is an opportunity to achieve historically known indicators. The number of stocks of this fish should play the role of an ecological balancer of the Caspian ecosystem, being the fourth link in the food chain in this reservoir and at the same time developing commercial cultivation of brook trout with the subsequent release of its juveniles into the Caspian basin.

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