Several years ago, Uzbekistan became an independent country and initiated the first steps towards the market economy. This has been also reflected in the new approach to the management of water resources. During the years prior to independence, the decision to grow cotton as a highly dominant crop was dictated by the overall policies and needs of the Soviet Union, and this led to the need for maximizing the utilization of water through river regulation. There are 26 irrigation reservoirs in Uzbekistan (excluding Karakalpakstan) covering 170 600 ha at present. The water is distributed through 13 000 km of canals and collected into 12 700 km of drains (collectors).

Construction of reservoirs was expected to provide challenge for the development of fisheries. However, at present only the large reservoirs are being utilized for this purpose, while the medium and small-size irrigation reservoirs, canals, large collectors and other reservoirs supplying agricultural needs are not used.

Uzbekistan reservoirs are situated predominantly in the basins of rivers Syr-Darya, Akhangaran, Zaravshan, Kashka-Darya and Surkhan-Darya. Many of them are the result of damming of rivers, but some were constructed far away from rivers in natural depressions, and are supplied with water by canals connecting them with rivers.

The total number of fish species and sub-species in Uzbekistan reservoirs is 86. The setup of fish fauna in the reservoirs is largely the result of historical evolution, but lately human activities have substantially changed the fish stocks in some of the water bodies. The development of irrigation systems interconnecting various river basins, and fish species transfer from drainages outside Central Asia have been the major two factors behind the changes.

As a result of the development of irrigation systems, Syr-Darya is now connected with the River Sanzar and the Sanzar with the Kashka-Darya. The latter one is connected through the main Karshin canal with the Amu-Darya and the Zaravshan is connected with the latter one through two canals, i.e. the Amu-Bukhara and Amu-Karakul canals. This irrigation net has played a major role in the establishment of the current set-up of fish stocks.

Attention has been paid recently to the negative impacts of irrigation on other uses of water resources, especially on fish and fisheries. In addition to the impact of water regulation, pollution from industries and non-point pollution from agriculture have interfered with the natural productivity of waters, with water quality, and this in turn has affected fish production potential of the water bodies. On the positive side, the human interference with water resources has resulted in a dramatic increase in reservoir water surface area, while the number of natural lakes has

decreased only marginally. In Khorezm district of the Amu-Darya basin major changes in water area redistribution have resulted from the formation of water storage lakes as a result of the accumulation of drainage and wash water in depressions.

In the Syr-Darya basin, a number of lakes in the delta of the river as well as on its floodplains have partially desiccated or completely disappeared. On the other hand, as a result of floods several lakes formed in Ferghana Valley and outside it, e.g. Arnasai, Tuzgan and Aidara. Since 1970 water level in these lakes started declining, but the decline has recently stopped, and the surface area in the lower Zaravshan has been increasing.

All the existing water bodies now contain fish which can be grouped under economically important and not important categories (Table 1) (see written version -same as Table 14). But not all water bodies have fishing activities. While fisheries on natural lakes date far back, those on reservoirs are of a recent date and are an organized activity of fishing companies. The fishery has been largely exploiting the existing fish stocks. The low fish production (see written version) is given by several factors: (i) the existing fish stocks are unable to fully exploit the existing fish food resources; (ii) the water bodies have poor spawning and nursery conditions for the economical important fish species; (iii) the set up of fish species in some water bodies contains only a few, or no fish species of economic importance.

This has led to the formulation of fishery resources management programme for a number of water bodies of Uzbekistan. It contains suggestions for increasing the production of economically important fish species through their best utilization of the natural productivity in each water body. The programme also addresses the best ways for organizing fisheries, both commercial and recreational. Implementation of the programme should lead to an increase in fish production to an average of 30 to 40 kg/ha/y, which could be 4 to 6 times higher than the present one.

Uzbekistan is a country with a predominantly dry desert climate situated in Central Asia. In the north it is delimited by the Ust-Urt plateau, in the north-east by the sandy desert Kyzylkum, and in the south-east by snow-capped mountain ranges. It is the rainfall and snowfall in the mountains, shared by Kyrgyzstan and Tajikstan, which provides this very dry country with most of its water. According to the information provided by the Gidroproekt Institute, in Uzbekistan 98% of water is now used for agriculture needs, 0.5% for domestic supply, and 1.5% for industrial needs.

The two major rivers passing through Uzbekistan are the Amu-Darya and the Syr-Darya, but there are also three other large rivers, Zarafshan, Surkhan-Darya and Chirchik which supply water to this thirsty country. Since the 1940s many irrigation canals and systems have been constructed, among which the most important are the Amu-Bukhara canal, irrigation canal system in the Hungry Steppe, Karshin Canal, and the canals of the Surkhan-Darya region. The large-scale irrigation system established for cotton production and other crops also includes a number of reservoirs. The Zarafshan River has several reservoirs, viz. Kattakurgan, Kuyumazar, Tudakul and Shurkul, constructed during the 1940s-1950s. Winter and spring floodwaters of the Kashka-Darya River are stored for irrigation in Chimkurgan (formed in 1958), Kamashin (1953) and Pachkamar (1968) reservoirs, and those of the Surkhan-Darya in Uchkyzyl (1955), Degrez (1953) and Yuzhnosurkhan (1965). There are several reservoirs in the Ferghana Valley in the Tashkent and Syr-Darya regions.

Uzbekistan has 3 000 km of rivers, 257 000 ha of lakes, and 125 000 ha of reservoirs. Lakes of fisheries importance are situated in the following regions: Khorezm, Bukhara, Syrdarya and Dzhizak (for example the Arnasai system of lakes, which covers 180 000 ha). The largest reservoirs are Kattakurgan (10 000 ha) and Yuzhnosurkhan

(6 500 ha).

Development of agriculture in the countries of Central Asia led to maximizing the use of the available water resources. This has had a major impact on the Aral Sea. It was a combination of the increased water demand with drought lasting over at least 20 years, which led to a reduced discharge into the Aral Sea through the two major rivers, i.e. Syr-Darya and Amu-Darya. This has led to a gradual desiccation of the sea, to increased salinity and to disappearance of fish. While during the 1950s the capture fishery harvested 35 000 to 40 000 t per year, today the Aral Sea has completely lost its fishery importance. In Uzbekistan now only reservoirs, rivers, natural lakes and lakes receiving drainage water are fished, but there is a growing pond culture fishery as well. New lakes have been created from the drainage water, viz. Arnasai lake system of the Hungry Steppe, Lake Alan in Karshi Steppes, lakes Dengizkul, Shurgak, Karakyr and Tuzgan in the Bukhara region, and some others in Khorezm region and on the lower Amu-Darya River.

Over the last 60 years, on the middle and lower Amu-Darya, over 6 000 km of irrigation canals have been constructed, together with the reservoirs Kelif and Tuyamuyun, and the pumping stations Amu-Bukhara and Karshin, which lift the Amu-Darya water 130 m high to feed Talimardzhan reservoir and Karakul canal and some others.

Regulation of Uzbekistan rivers has led to profound changes in the natural aquatic environment. Dams have stopped fish migrations and reservoirs have flooded natural spawning and feeding grounds. This has lowered the reproduction rate, which in turn, has resulted in a decline in the riverine fish stocks. Consequently, fish catches have declined. The situation has been further aggravated by the often irreversible water uptake for human needs. Not only are large volumes of water diverted for irrigation, industries, cooling of hydrothermal power stations, but the uptakes have diverted most of the young fish onto irrigated fields or into industrial sites. The level of this damage is about the same as that caused to fisheries by dam construction and pollution. The highest demand for irrigation water is during summer when water is rich in young fish. It is estimated that in the irrigation canals of Karakalpakstan alone 5 billion young fish perish annually (Pavlovskaya et al., 1968).

2.1 The Amu-Darya River

Those floodplain lakes situated many kilometres from a river, with river water reaching them only in autumn and winter experience a drop in water levels. In spring and summer. This may be accompanied by an increase in water salinity, which negatively affects especially the young of common carp and bream.

The pH in floodplain lakes ranges from 7.2 to 8.2, dissolved oxygen concentration from 8.2 to 17.7 mg/l, which corresponds to 90.6 to 198.4 % saturation. In several lakes (Abulkul, Khodzhakulgan and Tokizchokur) the dissolved oxygen concentration at the bottom declines to only 55% saturation in summer. The lakes ionic composition is dominated by sodium chlorides.

Khorezm region which covers 47 000 km², is an oasis situated on the left bank of the lower Amu-Darya. In the south and southwest it is bordered by the sands of the Karakum desert. The Amu-Darya River in Khorezm region has a strong current and is turbid. During floods the river often spills over the banks and forms a wide floodplain. The water of Amu-Darya in Khorezm region is diverted into a system of canals with a total length of 900 km. The length of collector canals totals 215 km. Northern collectors join collector Daryalyk and this in turn brings the drainage water into another large collector, which then joins with the drainage waters from the Khorezm and Tashauz regions and discharges water into the Sarykamysh depression.

A total of 36 fish species are known for the Khorezm region. Grass carp, silver carp, common carp, Turkestan barbel, roach, rudd are found among macrophytes and above hard substrates, such as sand, at the riprap of dams, in canals and collectors. Clay or clay-sandy bottoms have gudgeon, ostroluchka, goldfish, and above sand and usually in current are found riffle minnows and Amur stone loach. Close to riprap of dams are also found juveniles of Aral asp, pikeperch and silver carp, and during the spawning period also grass carp, silver carp and Aral asp. Many fish species and their juveniles (common carp, Aral asp, rudd, Aral roach, crucian carp, mosquito fish, barbel, shemaya, riffle minnow) are found in spring and summer in the littoral of lakes and reservoirs. After spawning the adults retreat into deeper water.

Running waters of the Khorezm region are inhabited by the rheofilic fish Amu-Darya stone loach, Aral barbel, shovelnose, Aral asp, razorfish, pikeperch. Those with preference for still waters are Aral bream, crucian carp, gobies, rudd, white-eye, pike, roach, ide.

The majority of commercial fish species mature in the second or third year (bream, wels, common carp, white-eye, roach, crucian carp, razorfish), and the low-value Turkestan gudgeon, striped bystranka, spiny bitterling, golden spiny loach, stone morokos which lay eggs during the first and second year. Aral asp and Turkestan barbel mature at the age of 4-6 years. Mature males are usually smaller than mature females.

Spawning of the riverine fish takes place during spring and summer. Asp, roach, pikeperch and white-eye spawn over a period of one week to one month, with the whole batch of eggs being released at once. The spawning period of the other species (serial spawners) may extend over 2-3 months.

Starting in mid-April large quantities of fish larvae and some juvenile pikeperch - up to 1.5 million within 24 hours - enter irrigation canals (Table 1). The larvae and juveniles are carried by the current. In May small pikeperch dominate in irrigation uptakes, but the number of fish is lower than in April. On average 200 000 juveniles and larvae enter the irrigation system every 24 hours through the two canals, starting from the pumping station. It is estimated that in May the pumping station lifts 27 million cubic metres of water from the Syr-Darya, and with it 4.5 to 5 million juvenile fish which end on irrigated fields (Table 1). During June-August the bulk of fish pumped into the canals are juveniles, but there are still some fish larvae as well.

Table 1. Juvenile fish incidentally pumped out from the Syr-Darya with irrigation water

In spring, when river water is murky and there is a strong current, the young fish cannot orientate visually and cannot resist the current and therefore enter the pumps. In summer the juveniles are bigger and more capable of resisting the current and in the less turbid water they can avoid the pumps.

Aquatic macrophytes represent a major problem for irrigation canals. This problem has been handled in the Karakum Canal by introducing grass carp. This canal, which branches off the Amu-Darya River, and its lateral lakes, has in the past experienced growth of aquatic plants on a large scale. To sort out the problem, grass carp was introduced in 1958 and released in large numbers in 1960 and 1961. By the mid-1960s, large-scale natural reproduction of grass carp took place and within a few years most of the aquatic macrophytes disappeared. Some problems, however, remained. Selective feeding of the grass carp led to succession in macrophytes, with Myriophyllum spicatum being replaced by Ranunculus, which is considered toxic to grass carp. Charyev (1984) who summarized the experience with the introduced Chinese carps into the Karakum Canal, emphasized the need to protect the higher aquatic vegetation, particularly in cases where macrophytes represent spawning substrate for other fish, such as common carp. The combination of three Chinese carps, viz. grass, silver and bighead, has been considered very suitable for maintaining good water quality, and at the same time the three carp species constitute 75 to 80 percent of the total catch from the canal and its associated water bodies.

Grass carp and silver carp stocks in reservoirs, lakes and irrigation canals depend on a number of variables, such as predatory fish, size of fingerlings of Chinese carps used for stocking, and the character of the water body itself. Good results are obtained if 2-year-old fish are stocked but hydrological parameters such as width, depth, transect of the canal, current velocity in it are also of importance and determine what size of fish to be stocked and when. The density of stocking grass carp will depend on the quantity of aquatic plants present in the irrigation system. Large canals should be stocked with 2-3 year old carps, small canals and collectors with 1-2 year-old. Large canals should be stocked in autumn, small canals and collectors in early spring. During the first year after stocking there is usually little effect on aquatic plants, but results become clearly visible during the second and third years.

Irrigation of the Hungry Steppe soils required construction of many collector canals, of a total length of over 1 000 km. The function of these canals was to collect the residual water from irrigated fields. The water entering collectors from fields has an elevated salinity and this encourages the growth of aquatic plants. Small collectors will overgrow with aquatic plants already during the first year. The first to appear are usually submersed filamentous algae, Potamogeton pectinatus and P. crispus, Zanichellia sp. and in some canals also Naias maritima and Ruppia maritima. Later on sixty percent of these are replaced by the reeds Phragmites communis and Typha angustifolia.

Much of the drainage and collector water is reused. This leads to a gradual increase in water salinity and to salinization of irrigated land. From the annual volume of 19 to 21 km3 of drainage water in the Amu-Darya river basin, 9.7 km3 is returned back to the river. Over the last 30 years water salinity in the lower Amu-Darya has increased to 3 g/l. Such salinity causes problems both in the irrigated fields and in water bodies receiving drainage water.

2.2 Floodplain lakes

The lower Amu-Darya lakes and lakes in the Khorezm region of Uzbekistan are fed by drainage and ground water. The lakes of the Khorezm oasis are of three types: those fed by the Amu-Darya water through irrigation systems; those which do not receive the Amu-Darya water but are connected through collectors with other lakes, and those which partially or completely dry out during summer. The chemical composition of water differs. Water salinity ranges from 1 044 to 3 040 mg/l are rich in plyto- and zooplankton. Mysids and freshwater prawns entered the lakes from the Amu-Darya and Syr-Darya and are also consumed by most fish species.

Floodplain lakes of the Amu-Darya in Uzbekistan still have good spawning and feeding conditions for the local fish. At present some 50 species of fish are found in these lakes, and 20 species are of economic importance. While common carp, pike and wels are heavily fished, the low-value species such as roach, dwarf common carp, goldfish, and perch are neglected. As a result, stocks of low-value fish are high. Fish yields in lakes average about 15 kg/ha. Currently, attention is being paid to increasing the fish production of Lake Tuzgan (Dzhizak region) and Ulli-Sharkul (Khorezm region), which cover some 32 000 ha. Management measures proposed are stocking of mysids and introduction of gammarids from the River Don delta and from Mingechaur reservoir. Another proposed measure is to develop combined fish stocks of common, grass and silver carps.

Enhancement of lake and reservoir fish production has become a priority with the collapse of the Aral Sea fishery. In the Khorezm region, situated in the Amu-Darya delta and one of the oldest agricultural areas in the world, there are more than 100 water bodies suitable for fisheries. Since 1974 Khorezm Fish Farm, with 900 ha of ponds, has been producing 2 600 - 2 900 kg/ha of fish. The total fish pond harvest is about 20 000 t/y. The pond area will be expanded to 1 500 ha. Fisheries managers hope also to harvest a total of 5 000 t from open waters of this region. and there are plans to convert lakes with low fish production into managed fish-producing water bodies.

2.3 Reservoirs

Uzbekistan reservoirs total over 20 and cover 110 000 ha. Of the 80 species listed for Uzbekistan reservoirs, twenty have economic importance. A fishery exists on seven reservoirs. The catches change from year to year. In 1970 the total catch from reservoirs was 328.8 t, in 1975-1979 it ranged between 100 and 200t. Reservoir fisheries management has focused on the following:

- introduction of new fish species and fish food organisms

- management of spawning sites, fish protection, improvement of the efficiency of fishing methods

- intensification of fish production in separated or isolated parts of reservoirs

- fish production in the littoral zone

- pond and cage culture.

Reservoirs Kattakurgan, Kuyumazar, Tudakul and Chimkurgan, which have low or no stocks of introduced fish, have also very low yields. Common carp, which forms 15 to 20% of all fish stocks, is the most important economic fish species.

Reservoirs in the semi-desert or desert areas, viz. Farkhad, Kairakkum, Kattakurgan, Kuyumazar, Tudakul, Chimkurgan and Uchkyzyl have a relatively low primary and secondary production and therefore poor fish food resources. In spite of that, the introduced Chinese carps which feed on macrophytes and plankton, became well established in some of these reservoirs (e.g. Chimkurgan). This shows that such reservoirs have good fisheries potential, and that the estimate of natural fish food production should not be based on standing crop but on turnover rate, which, due to the high water temperature and insulation is believed to be high. There is a need for fundamental studies on the primary and secondary productivity of reservoirs, as well as on biology and fish dynamics, both for the native and introduced fish species.

During the 1950s to 1980s the following fish species were released in Uzbekistan reservoirs: goldfish, Aral bream, pikeperch, silver carp, grass carp, bighead carp and some other species of fishery importance. Together with them, 15 species of low-value fish were also incidentally introduced. While the first group of fish was becoming established, the fish of the second group, due to their high adaptability to new conditions, quickly spread though the water bodies of Uzbekistan. As a result, the original fish fauna composition has changed considerably. Some valuable fish species such as khramulya, Turkestan barbel and shemaya, as well as the less valuable Zarafshan dace, ostroluchka, gudgeon, riffle minnow have become rare.

The proposed management measures include stocking of Chinese carps, establishment of artificial spawning substrates, and expanding closed seasons and closed areas. Regular stocking of the common carp and Chinese carps should increase the reservoir fish yield to 40-50 kg/ha, resulting in an annual reservoir fish catch of 1 600 to 2 000 t of fish.

Establishment of reservoirs has had a positive impact on the growth rate of the wild form of common carp. In the Amu-Darya reservoirs Uchkyzyl, Dagrez, Yuzhnosurkhan and Chimkurgan a two year-old common carp ranges between 14.9 and 16.8 cm length, while in the rivers Kafirchirgan, Surkhan-Darya and Amu-Darya (region Termez-Aivaj) the length is only 10.5-12.1 cm. A four-year old carp in Surkhan-Darya and Amu-Darya is 21.3-22.3 cm long, in reservoirs 25.3-28.1 cm. The fast growth rate in reservoirs is noticeable and this is surprising as the carp there feeds on plant detritus. In reservoirs, common carp faces the problem of finding suitable spawning sites, as a rapid drop in water level due to irrigation demands is common. As a result, fertilized eggs of carp, bream, crucian carp and wels usually die. Nevertheless a large fishery development potential exists in Uzbekistan reservoirs and can be realized by regular stocking of hatchery-raised fingerlings. Further intensification is possible through developing semi-intensive fish culture in cages, which could be made largely independent of reservoir water level fluctuation. Induced breeding could be practised on fish other than Chinese carps, such as Turkestan bream and Aral asp, khramulya and snowtrout which require river currents and are migratory. Both conditions are no longer available to them.

Current fish yields of Uzbekistan reservoirs range between 7 and 30 kg/ha and this is considered to be low. At present any increase in catch is achived through an increase in fishing pressure.

Lakes, as well as reservoirs, have major importance for fish and fisheries. Due to the high silt load, turbidity and fast current, as well as rapid changes in discharge rates, the rivers Zarafshan, Surkhan-Darya and Kashka-Darya have little fishery importance. In summer Kashka-Darya completely dries out while Surkhan-Darya and Zarafshan carry only a small amount of water.

Factors that determine the current low fish production of Uzbekistan reservoirs and other water bodies are still not clear enough to allow formulation of sound management strategies for a steady increase in fish yields. It is probable that each reservoir and lake may require a specific approach. The management measures need to address protection of the existing fishery resources, especially of the riverine fish of the Syr-Darya, Amu-Darya and Zarafshan, current levels of fishing pressure, ways of increasing fish stocks in the individual reservoirs and floodplain lakes. Special attention needs to be paid to small lakes and the potential for converting them into semi-intensive well managed fisheries bodies.

REFERENCES

Abdullaev, M.A., 1969. Biological basis of rational reservoir fisheries in the desert zone of Uzbekistan (river basins of the Bukhara and Kashka-Darya regions). Ph.D. thesis, Tashkent. (in Russian)

Abdullaev, M.A. and D. Urchinov, 1989. Economically important fish in water bodies of the lower Zeravshan River. Tashkent, Pub. FAN. (in Russian)

Amonov, A., 1985. Fish ecology of water bodies in the south of Uzbekistan and neighbouring republics. Tashkent, Pub. FAN. (in Russian)

Berg, L.S., 1948-9. Freshwater fish of the USSR and neighbouring countries. (in Russian)

Charyev, R., 1984. Some consequences of the introduction and acclimatization of grass carp, Ctenopharyngodon idella (Cyprinidae) in the Kara Kum Canal. J.Ichthyol. 24 (3): 1-8.

Nikolsky, T.V., 1940. Fish of the Aral Sea. MOIP.