The Ob River is one of the largest rivers in the world. The basin area, about 3 million km2, is the largest in Eurasia. The main part of the basin is located in the West Siberian Lowland in territory of the Russian Federation (Fig. 1). The part of the basin with the Russian Federation only that may be used for fishing industry is colossal (156 km2). Stocks of whitefish (Coregonus sardinella, C. autumnalis, C. peled, C. tugun, C. lavaretus pidschian, C. muksun, C. nasus, Stenodus leucichthys nelma) are the main fishery resources of the Ob River basin, considering its climatic features.  

FIGURE 1. Map of whitefish farms in the Ob basin.1 – Kharp hatchery, 2 – the egg collection base Rahtynya, 3 – Ugra hatchery, 4 – Tobolsk regional fish farm, 5 – Lake Volkovo, 6 – Kyshtymskoe fish farms, 7 – Chebarkul hatchery.

FIGURE 2. The species composition of the total catch of whitefish in the Ob basin in 2015.

An average of 11,000 t of whitefish was caught in the 1970s to 1980s, but natural stocks of whitefish have declined significantly in recent years. Annual catches have fallen from 6,120 t in 2004 to 4,730 t in 2014. The total catch of whitefish in the region dropped to a record low value of 3,001 t in 2015 (Fig. 2). The most catastrophic situation is with C. muksun. Catches of this species decreased from 552 t to 51 t during the same period. This has resulted in a temporary ban on commercial fishing of C. muksun and S. l. nelma since 2015. The main reasons for the decline in whitefish resources are pollution of the feeding and wintering zones of whitefish by the oil industry and longer periods of low water level that occurred in the basin from 2008 to 2013.

Artificial Propagation and Stocking of Floodplain Lakes

To compensate for negative impacts on whitefish populations, there has been an increase in artificial propagation activities. According to biologically-based calculations, the annual needs for basin recruitment of whitefish fry range from 0.3 to 1.6 billion. The current approach of stocking the Ob River basin is mass-scale stocking of whitefish larvae in specifically selected small floodplain reservoirs immediately after ice breakup. The basic requirements for such reservoirs are a small number of predatory fish due to winter freezing and the availability of a hydrological connection with the river during summer floods. Mass appearance of juvenile whitefish in the river channel starts when the river water level begins to recede after the flood peak and water in floodplain lakes warms to 16-18 C. By this time, juveniles reach about 1-5 g. The average survival rate of stocked larvae is 40 percent. The total number of juvenile grown this way reached 106 million in 2009. There were 92 million juveniles released in the Ob River basin in 2015, including 74 million C. peled and 13 million C. muksun (Fig. 3).

Extensive Aquaculture of Whitefish in Lakes

The role of commercial whitefish farming is growing in the context of declining stocks of commercial fish from natural populations. The main form of whitefish aquaculture in the Urals and Western Siberia is extensive farming in lakes. The main species of lake fisheries are C. peled and its hybrids. Currently, about 3,000 t of whitefish are caught from small- and medium-size lakes in the forest-steppe and steppe zones of the Urals and Siberia. Most lakes stocked with whitefish have no other fish at all or have only crucian carp, which does not prey on whitefish larvae. This is the main factor that determines survival rate of early larval whitefish in these lakes, even without rearing. Single-season growing of whitefish usually requires lakes of 1 to 50 km2 with an average depth of 2-3 m, a water salinity 1-8 g/L and pH of 7.5-9.0. These lakes are usually eutrophic and the average concentration of zooplankton is 2-10 g/L. Usually whitefish larvae are stocked at 1-5 days of age at 3-5 mg in weight and 7-9 mm in length. Sometimes larvae are grown for 5-10 days in hatchery tanks and fed with Artemia nauplii before being stocked in lakes. The stocking density of larvae in lakes is 1,000-4,000/ha. Whitefish reach an average weight of about 100 g (Fig. 4) during the first growing season (May to October) and then are captured for processing and marketing.

Fingerlings of hybrid C. peled and C. nasus are 30-40 percent larger in weight than C. peled. Therefore there is more demand for stocking hybrid whitefish; as many as 200 million hybrid larvae are sold annually. A 30-y statistical analysis has shown that the average stocking of 1 million larvae provides a harvest of 11 t of commodity C. peled fingerlings. The maximum value of this indicator reached 70 t from 1 million larvae. On average, the seasonal catch of first-year whitefish is 26 kg/ha, with a maximum of 114 kg/ha, providing a commercial return of 13 percent. In the most successful cases, commercial returns reach 50 percent. This form of extensive aquaculture is highly remunerative in these lakes.

Commodity whitefish fingerlings are grown in lakes because of the availability of natural food resources. In this regard, buying whitefish larvae for stocking lakes and harvesting market-size fish are the main expenses of a fish farmer. First-year whitefish are processed into salted, dried or smoked forms that are considered to be a delicacy. Thus, there is a large consumer demand for these products at all times.

The main risk of production failure is connected with excessive summer warming of lakes in some years. In this case, complete mortality of fish in small lakes may occur. In addition, a large number of fish-eating birds, especially cormorant Phalacrocorax carbo, significantly reduces the effectiveness of growing whitefish in lakes, as well as poaching. Whitefish fisheries are also adversely affected by the uncontrolled dispersal of fish species such as Perccocottus glenii from the Far East and Leucaspius delineates from the European part of Russia. These alien fish species have a high tolerance for oxygen deficiency in winter and spring and represent a serious threat to whitefish larvae. In addition, they reduce the share of food resources potentially suitable for the consumption by whitefish. The most damaging parasitic disease of whitefish grown in lakes is caused by trematode larvae of the genus Diplostomum.

Two- and three-year growing of whitefish is carried out in lakes with a favorable winter oxygen regime. In this case, the size of whitefish reaches 300 g after the second year and 600 g after the third year. If a lake has an existing fish community, one of the major conditions for successful growing is the use of relatively large-size stocking material. Usually such lakes are stocked with fingerlings that are grown in special lake-nurseries. In some cases, aeration equipment is installed in lakes to ensure suitable conditions for overwintering. However, such intensification measures significantly increase the cost of the resulting fish products. Therefore, ponds with two or three-year production cycles account for less than 10 percent of C. peled and its hybrids.

In addition to C. peled, large forms of European vendace C. albula ladogensis and C. lavaretus maraenoides have been grown in small and medium size, relatively deep man-made lakes of the Urals for over 50 years. As objects of aquaculture, these whitefish were brought to the Urals from Ladoga and Peipus Lakes in the 1930s. In 2015, 147 t of C. albula ladogensis and 5 t of C. lavaretus maraenoides were harvested.

Given the area of suitable lakes, the scope of extensive aquaculture of whitefish in the south of Western Siberia and the Urals can be increased to 21,000 t. However, implementation of these plans is constrained by a number of legal and organizational problems.

Read the rest of this article in the March 2016 issue of World Aquaculture Magazine here