Issyk-Kul Hegarkuni Trout. Salmon Family.
There are 8-9 rays in the dorsal fin (III—V), 8-9 in the anal fin (III); there are 104-117 scales in the lateral line. In Issyk-Kul, it can reach a weight of 17 kg or more. Following the recommendation of Academician L. S. Berg, Hegarkuni trout was introduced to Issyk-Kul from Lake Sevan (Armenia) in the form of fertilized eggs in 1930 and 1936. The first batch consisted of 750,000 eggs, and after the larvae hatched, they were released into the Irdyk Bay (near the mouth of the Jergalan Bay). Subsequently, another 800,000 eggs were brought in, and after the larvae were incubated, they were released at the mouth of the Ton River.
In general, the stocking of such a vast body of water as Issyk-Kul with trout larvae seemed to be a rather unpromising endeavor, as they could easily be destroyed by local fish, especially by the golts, which were abundant in the bays, inlets, and river mouths at that time. However, starting from 1937-1940, local fishermen reported catches of young trout in the pre-mouth areas of rivers in various locations around Issyk-Kul.
To the surprise of the researchers themselves, unexpected transformations began to occur with the Hegarkuni fish in Issyk-Kul. First of all, its length and weight increased significantly in the new environment. While individuals measuring 60 cm and weighing 4 kg are extremely rare in Sevan, in Issyk-Kul, the fish began to grow to nearly 90 cm in length and reach weights of 10 kg. Remarkably, the growth rate increased by at least one and a half times.
Upon studying this phenomenon, it was found that the Hegarkuni in Issyk-Kul had become a predatory fish: 82% of the diet of the Issyk-Kul form consisted of small fish, most often golts.
The Hegarkuni in Issyk-Kul also changed in color and body proportions. While the Sevan Hegarkuni was characterized by purple and lilac tones, the Issyk-Kul variant is densely covered with brown spots of serrated, rounded, cross-shaped, or ring-like forms. Under the new conditions, the fecundity of females increased several times.
In December 1941, a mature male trout measuring 54 cm in length and weighing 2275 g was caught for the first time at the mouth of the Ton River.
From the mid-1940s, adult mature trout began to frequently appear in fishermen's nets along the southern part of the lake at the mouths of the Ton, Ak-Sai rivers, as well as in the eastern part of the lake near the mouth of the Jergalan River.
The acclimatization of the Hegarkuni demonstrated how adaptable and changeable salmon can be and how easily they adjust to altered living conditions.
In November 1946 and 1947, local fishermen began to systematically catch trout in the rivers of the southern part of the lake — Jety-Oguz, Barskaun, Tosor, Ton, and Ak-Sai, where they were heading to spawn. Some individuals reached weights of 10 kg. This led to the predatory extermination of the spawning fish. Poachers set nets in the pre-mouth sections of the rivers, while trout entering the rivers were caught with dip nets and speared. The riverbeds were completely blocked with brushwood fences with openings for setting dip nets, where fish would get trapped. Thus, the migration route of the trout to their spawning grounds was completely obstructed, eliminating the possibility of natural reproduction of this valuable fish.
The fish protection service faced the issue of organizing more effective protection for spawning trout populations and establishing fish breeding farms for the artificial reproduction of its stocks in Lake Issyk-Kul. The necessity of constructing a fish breeding farm for raising trout fry was also dictated by the fact that numerous tributaries of Issyk-Kul were unsuitable for the spawning of this fish, as their flow was diverted for irrigation purposes, leaving the riverbeds dry throughout the summer until late autumn. Therefore, following the recommendations of the republic's ichthyologists, the construction of a fish breeding farm began on the Ton River. It was only put into operation in 1964, with significant delays.
The biology of Hegarkuni trout was well studied by B. P. Luzhin, who established that it grew significantly faster in the conditions of Issyk-Kul than its ancestral form in Lake Sevan. There were cases of catching trout over a meter in length and weighing 23 kg in Issyk-Kul. Proportionally to its growth, the fecundity of the Issyk-Kul trout also increased. This is explained by the fact that in Lake Sevan, Hegarkuni trout primarily fed on the amphipod Gammarus, while in Issyk-Kul, it became predatory, consuming non-commercial fish, juvenile fish, and fry of other species, which contributed to its rapid and significant growth.
Incidentally, the water of the lake is more oxygen-saturated than that of Sevan and other lakes. This factor may have contributed to the changes in Hegarkuni.
In Issyk-Kul, Hegarkuni trout reaches sexual maturity at 3-5 years of age, with males maturing a year earlier than females. For most of its life, trout reside in the lake. Here, they spend their feeding period, hibernate, and only enter the rivers for spawning. In the pre-mouth areas of the tributaries of Issyk-Kul, the formation of spawning trout schools occurs in September-October. Some individuals, mainly males, enter the rivers along the southern shore of the lake as early as October, but the entry of trout schools into spawning rivers begins in November, when the water temperature in the rivers drops to -3 to -5°C, and continues until January. Some individuals enter the rivers to spawn in January and even February.
Fish