Fish introductions in the former Soviet Union: The Sevan trout (Salmo ischchan) — 80 years later

Abstract

The Soviet Union played the leading role in fish introductions in Eurasia. However, only 3% of all introductions prior to 1978 gave a commercial benefit. One of the noteworthy examples appears to be the Sevan trout (Salmo ischchan Kessler, 1877)-an endemic salmonid of Lake Sevan in Armenia. This species has been introduced to Kirghizstan, Kazakhstan, and Uzbekistan, however, only the Kirghiz population has persisted in relatively high numbers. In this paper we provide the first extensive molecular study of S. ischchan using samples from the native population from Lake Sevan and three hatcheries in Armenia, as well as from the population introduced to Lake Issyk Kul in Kirghizstan. The Kirghiz population has been isolated since the introductions took place in 1930 and 1936. Our results, based on 11 nuclear microsatellites and a 905 bp fragment of the mitochondrial control region suggest that hatcheries have maintained genetic variability by way of ongoing translocations of individuals from Lake Sevan. Simultaneously, significant Garza-Williamson M-values suggest that bottlenecks could have reduced the genetic variability of the wild populations in the past. This hypothesis is supported by historical data, indicating highly manipulated waterlevel regulations and poaching as two main factors that dramatically impact fish abundance in the lake. On the other hand, a similar situation has been observed in Kirghizstan, but this population likely rebounded from small population size faster than the other populations examined. The Kirghiz population is significantly genetically differentiated from the other groups and have morphological features and biological attributes not observed in the source population. Genetic data imply that the effective population size in the native population is lower than that found in the introduced population, suggesting that some active protection of the Lake Sevan population may be needed urgently.

Short Communication: Mollusks biodiversity of Lake Sevan, Armenia

“…Numerous rivers and temporally active watercourses drain from the North-East coast (RABE 2010). The Sevan trout, Salmo ischchan (Kessler, 1877), is an endemic fish species of Lake Sevan in Armenia (Bogdanowicz et al 2017).…”

Experimental Validation of Suitability of a River for Natural Reproduction of Trout of Lake Sevan Using Egg Incubation

“…Possible restocking by the population from Lake Issyk Kul was also disputed as the recent findings based on molecular and morphometric analyses are rather controversial. Particularly, molecular analysis shows significant difference between the populations from various farms in Armenia and from Lake Issyk Kul [17] while morphologically Kyrgyz and wild populations from Lake Sevan are closer than the wild populations and trout released from fish farms in Armenia [25]. Considering also the risk of domestication when restocking with farm-grown fish, it was supposed that incubation of eggs directly in the river would be an alternative and rather efficient solution for restocking Sevan trout [24] taking into account the homing reflex of fish.…”

“…Until the 1970s, it was represented by four subspecies (morphs) differing in terms of breeding times and places, as well as growth rates [14,15]. Particularly, winter bakhtak (S. ischchan ischchan Kessler, 1877) (growing up to 90 cm and reaching 15 kg) and bodjak (S. ischchan danilewskii Iakowlev, 1988) (dwarf, slowly growing lacustrine fish, not exceeding 33 cm and 250 g) bred in the lake while summer bakhtak (S. ischchan aestivalis Fortunatov, 1926) bred both in the tributaries or near the river mouth; gegharkuni (S. ischchan gegarkuni Kessler, 1877) bred exclusively in the tributaries [15][16][17][18]. While increased water diversion for irrigation and energy generation has led to extinction of winter bakhtak and bojak [19] due to loss of spawning ground in the littoral zone, poaching in river mouth parts has significantly reduced the populations of summer bakhtak and gegharkuni.…”