Sander - Asp

Zander - Zander lucioperca - Lucioperca lucioperca

The zander is a typical lake-river fish that can also live in brackish areas of the seas.

Successfully acclimatized in our water bodies, this predator was introduced in the mid-20th century. Its acclimatization was particularly successful in Lake Issyk-Kul, where it found favorable conditions for reproduction and growth. However, the introduction of zander into Lake Issyk-Kul caused significant damage to the indigenous fish, many of which are endemics, especially the beloved loach.

On the recommendation of the famous ichthyologist F. A. Turdakova, zander was brought to Lake Issyk-Kul in 1958 by workers of the Glavrybvoda from Lake Zhizhitskoye in the Pskov region with fertilized eggs (500,000 pieces), after which 450,000 larvae were released into the Tyup Bay following incubation. In the same year, 1,400 zander breeders were brought from the mouth of the Ural River (Guryev) and released into the Rybachinsky Bay. About a month after the release, zander migrated to the eastern areas (Tyup and Dzhergalan Bays).

Justifying the feasibility of introducing zander into Lake Issyk-Kul, F. A. Turdakova aimed to use this predator to suppress the population of small non-commercial species and loach. He wrote: “According to rough estimates, there are about 130,000 centners of loach and nuisance fish in the lake. If we also consider the juveniles of commercial fish, it seems not difficult to annually fatten 6-10 thousand centners of predatory fish on this basis.” Unfortunately, the idea of reconstructing the ichthyofauna of Lake Issyk-Kul lacked scientific basis and therefore resulted in ecological and economic losses.

Finding favorable conditions for reproduction and a rich food base in the form of nuisance fish (bullheads, gudgeon, loach) and a mass of small commercial fish — loach, zander quickly formed commercial stocks. As expected, it occupied the most brackish areas of the lake — Tyup, Dzhergalan, and Pokrovsky Bays, where the largest rivers — Tyup, Dzhergalan, and Chon-Kyzyl-Su flow in. These bays were the most fish-productive areas of Issyk-Kul before the introduction of zander, where about 30% of the annual fish catch in the lake was obtained. Since the 1970s, loach and carp have fallen out of commercial fishing in these areas due to the depletion of their stocks by zander and irrational fishing practices.

Zander reaches sexual maturity in Lake Issyk-Kul at the age of 3-4 years. Spawning occurs from April to mid-May. Zander spawns in the backwaters and bays of the lake on sandy-stony substrates. Submerged bushes of last year's reeds or plant roots serve as a substrate for egg deposition. Before laying eggs, females create a kind of nests in the sand — depressions, where they lay eggs, which are zealously guarded by males until the larvae hatch.

According to Yu. M. Tairov, some zander enter the Tyup River for spawning, moving up it for 30 km to the San-Tash state farm.

Zander has quite high fecundity, reaching up to a million eggs or more. However, despite this, the survival rate of its offspring, as well as that of other fish species, is extremely low — out of 100,000 laid eggs, only one fish survives to maturity. A lot of eggs and juveniles die from sharp temperature fluctuations, during storms, and from numerous enemies (larvae of aquatic insects, egg-eating fish, etc.). Many juveniles in their first year of life are eaten by predatory fish — adult perch, asp, catfish, and zander. Therefore, fish, like other living organisms, have developed a number of adaptations (physiological, morphological, behavioral) in their historical development to ensure the survival of the species. Thus, the high mortality of offspring in fish is compensated by their high fecundity.

After spawning, zander switches to active feeding, moving to deeper areas and hunting for food in small groups or alone. In the early years of zander's naturalization in Issyk-Kul, it mainly fed on small non-commercial fish (gudgeon, bullheads, loach) and loach. However, when the stocks of nuisance fish in the lake sharply decreased, zander switched to feeding on loach and juveniles of other commercial fish (loach, carp, tench, bream) and its own juveniles. Larger tench, small carp, and even loach cannot be taken by zander due to its narrow throat. Therefore, it has to settle for small fish.

In the first year of life, benthic invertebrates — insect larvae, crustaceans (amphipods, mysids) play an important role in the diet of zander juveniles, but as zander grow, they switch to feeding on juveniles of other fish species. It has been noted that juvenile zander are mainly active during the daytime. In contrast, adult zander are active during twilight and nighttime when their prey leads a less active lifestyle. Active biting in adult zander is observed before sunrise and after sunset.

Unlike pike, zander avoids areas of the water body that are heavily overgrown with vegetation. It also shuns silted substrates, preferring sandy-stony ones. It readily settles under steep cliffs in deep areas. Generally, large zander leave the shallow zone after spawning and move to deeper waters. Throughout the year, zander in Issyk-Kul forms two well-defined shoal aggregations in the shallow zone of the lake — a spring spawning aggregation (from mid-March to mid-May) and an autumn feeding aggregation (September - November). These seasonal aggregations coincide with its fishing. Zander is caught using set nets and shore-dragging seines. The most successful catch occurs in April - May when it approaches the shallow zone for spawning. At this time, 35 to 60% of the annual catch is obtained.

After depleting its food base in the eastern part of Issyk-Kul, since the mid-1970s, zander has begun to spread to the north and south of the lake towards the west, depleting the stocks of local loach populations along the way. Only the intensification of zander fishing will allow for a reduction of its negative impact on the stocks of peaceful fish.

The number of zander in the lake can also be reduced by placing artificial spawning grounds in its breeding areas, then collecting the eggs laid on them in separate containers for aquaculture purposes.

For this, fertilized eggs should be incubated in aquaculture trays, and the hatched larvae should be raised to viable juveniles, which can then be used to stock reservoirs.

Fish