The Neka river originates from Shah-Kouh Mountains in the eastern part of Mazandaran Province and flows westward parallel to the Caspian Sea coastline. Near the village of Ablo (vicinity of the town of Neka) the Zarandin tributary joins the river. Seven km south of the town of Neka, the river leaves the mountains and flowing northward across a flat country, enters the Caspian Sea. The river's watershed area in the region where it emerges from the mountains is about 2 400 km2.
The total length of the Neka river is 176 km. The average width of its river bed is 10–15 m. In some areas the river bed narrows (Nouzar-abad 5–6 m), in other areas it is wide (Ablo 40–50 m).
The temperature of the Neka river's water varies directly as the air temperature of the surrounding country. During 200 days a year the average temperature of the air is about 17°C and the number of days with below-zero temperature does not exceed 30 days a year. The maximum air temperature is as high as 35°C.
The Neka has been visited in six stations. The river bed in Padjim (probable dam construction site) is rocky and stony; in Ablo and Hadji-abad it is covered with rubble (diameter 10 cm) and gravel; in Bazmin-abad and Nouzar-abad the bed is clayey and silty. In all these stations the river banks are mostly composed of clay and downstream of Ablo their height is 2–6 m. In the period of springtime floods, the river, in its lower part (several kilometres upstream of Nouzar-abad), overflows the banks and inundates 23 000 ha of surrounding country comprising 9 000 ha of woods, pastures, thickets of indigenous trees and bushes, ponds and rice fields, the remaining 14 000 ha of flooded land being used mainly for cultivation of cotton.
This river plays an important role in the reproduction of valuable commercial fish of the Caspian Sea. Every year a great number of anadromous fish (kutum, common carp, Caspian roach, barbel, some eturgeon and “Sevruga”) as well as indigenous fish spawn in this river.
A considerable amount of biogenous substance carried down by the waters of the Neka river ensures reproduction of food organisms (both vegetable and animal) on which fish larvae and fry feed during the period of their life in the river proper and in the preestuary area of the sea.
At present the Ministry of Water and Power of Iran (Technical Bureau of the Water Division) in accordance with the Atrak and Neka Project is considering construction of a dam with reservoir for the purpose of meeting irrigational and municipal demands for water as well as with the aim of producing electric power. Six possible dam construction sites are being explored now, the Padjim station (71 km upstream of the river's mouth) being the most probable one.
It is planned to erect a 100 m high dam at this site. In that case, the future reservoir will be 7.5 km long and its width will be 0.5–1 km in most places. Maximum volume of water in the reservoir will amount to 235 million m3 and the lowest level of water will be in July–August.
Annual consumption of the reservoir's water will equal 110–120 million m3. Three possible variants of water consumption distribution are given in Table 9.
Present water discharge of the Neka river ensures annual influx equalling 123 million m3 of water. After construction of the dam and impoundment of the river, almost all this water will be used for irrigation, municipal demands and production of electric power. Besides, construction of another dam is envisaged in order to store the water discharged through turbines in non-irrigation periods with a view to its subsequent utilization for agricultural consumption. Therefore, the amount of water flowing in the lower Neka and being supplied mainly with waters of the Zarandin tributary will decrease till ½–⅓ of its pre-impoundment amount, at the minimum.
With the exception of high-water years (once in every five years), this situation will cause a sharp decrease of water flowing in the Neka river. Thus, the dam with the reservoir construction project which provides for the utilization of a great amount of the Neka river's water will do considerable damage to the fish stocks in the river due to the following reasons:
Considering the fact that productivity of future fish generations depends on abundance of water while, according to the documents of the dam construction project, water supply in the principal spawning months of the Neka river's fish will be reduced by one half or even more, it can be assumed that the number of the majority of the Neka river's commercially valuable species will diminish in the same ratio, i.e. it will constitute one half or even one third of its present number. As regards the common carp and the Caspian roach, their number will be reduced in much greater proportion (as compared to other species) and will go down to a minimum. This prediction is based on the fact that after construction of the dam, the Neka will not overflow its banks in spring and 23 000 ha of land normally inundated by floods and serving as a spawning area for the common carp and the Caspian roach will not go under the water. Consequently, these species' spawning grounds will be lost and multiplication of common carp and the Caspian roach in the Neka river will cease almost completely.
Construction of a dam with reservoir will result in a decrease of the amount of biogenous substances present in the Neka river which in turn will cause reduction in the amount of fish food both in the river and in the sea (its preestuary area).
Therefore, construction of a dam with a reservoir on the Neka river and utilization of a great volume of water for irrigation, electric power production and municipal water-supply will cause drastic changes in the river's hydrological and hydrobiological conditions and is going to inflict a considerable damage to fish stocks which cannot be compensated by natural reproduction of fish. The simplest and most economic way of compensating the damage which will be done to fish stocks is artificial fish cultivation. To accomplish this, a fish culture station should be established there.
In view of the proposed dam on the Neka river and the utilization of its water, a 100 ha spawning-and-rearing fish culture station should be constructed if the river's commercially valuable fish stocks are to be maintained. The main species to be reared at this establishment should be common carp (Cyprinus carpio L.) and kutum (Rutilus frisii kutum). These are the most valuable food fishes in Iran and they are very popular with the people in this country. Once the biological techniques of cultivation of the above-mentioned fish are mastered, the work on propagation of some other species could be started in the process of mixed rearing their young with young common carp and kutum.
The spawning-and-rearing piscicultural establishment could be set up on one of the plots adjacent to the Neka riverbed, downstream of the town of Neka, where the flood-lands are inundated in the spring season. The following ponds and production premises should be constructed on the chosen plot of land (See Fig. 6):
Four ponds, 24 ha each, for rearing of young common carp and kutum (two ponds for either species).
Four ponds, 0.25 ha each, for spawning of the common carp's brood fish (one female and one male require a spawning bed of 50–60 m2 area; therefore, one pond should not be stocked with more than 50 females and 50 males).
A canal for water supply and drainage.
A 230 m2 room for incubation of the kutum's eggs and collection of its larvae.
A 10 m2 room for fish culture implements and equipment.
A 30 m2 room for service personnel.
The fish culture station should be separated from the river by earthen dykes. The spawning ponds should be constructed near the ponds where young common carp is reared. All the ponds should be completely drainable. The spawning ponds' depth should range from 0 to 1 m, while the rearing ponds should be 0.5–1.5 m deep. The spawning ponds' bed should be thickly sown with soft submerged aquatic vegetation. A canal should connect the ponds to the river. This canal will supply the river water to the ponds in the springtime, while in summer season the water with reared young fish will be let out by this canal from the ponds into the river (as a result of the difference between the river's water level and that of the ponds in the spring and summer). A bulkhead gate should be installed in the canal's upper part, where it is to be connected to the river. A bulkhead gate should also be installed in each pond. This gate is opened when the water is let in during filling of the pond and when the water is let out of the pond along with reared young fish. The upper gate (on the river) should be fitted with a grate preventing outside fish from entering the fish culture station during filling of the ponds. Water collector ditches ensuring complete drainage of the pond's whole area and providing for concentration of reared young fish in these ditches after the drainage, should be dug out along the ponds' bed. When, during 20 days, the rearing ponds are filled completely two by two, the water consumption rate of the spawning-and-rearing fish culture station will amount to some 0.5 m3/sec.
The kutum and common carp cultivation techniques are not complicated, but it requires certain skill and accuracy at all stages of the production cycle.
Mature spawners should be transported to the fish culture station from an estuary or coastal area of the Caspian Sea, where the fish catching stations are located. Once the common carp brood fish have spawned and the kutum spawners' reproductive products are taken for the eggs' fertilization, these fishes could be sold on the market. The common carp and kutum's posterity will be raised in separate ponds. When the young fish reaches the migratory stage of its development which usually occurs at the age of one-and-a-half or two months, they are counted and released with water from the ponds into the river. At this stage, a young kutum will have individual average weight of 1.0 g, a young common carp - 2.5 g. These young fish will migrate down the river to the Caspian Sea.
Catching of the kutum spawners should be started in March. In case there will be some spawners with unripe reproductive products being on the fourth stage of development, they should be kept till complete ripening of the products in wooden lattice live-boxes of 3 × 2 × 1.5 m dimensions. The live-boxes should be installed in the river. The males and females should be kept in separate live-boxes. The boxes with males should be installed upstream while those containing females are to be set up downstream. Time of keeping the brood fish in the live-boxes ranges from 3 to 15 hours. Afterwards, the ripe reproductive products can be taken from the fish. Eggs and sperm should be procured by method of stripping. To do this, two females' eggs should be stripped into an enamel basin and the sperm obtained from three males should be poured over it. The fertilized eggs should be washed with water for 40–60 minutes. As a result, the eggs cease to be sticky. Then the eggs should be loaded into Ses-Grin incubators which could be installed in the river. Otherwise, the eggs can be incubated in Weiss apparatuses or Youschenko incubators which are normally installed in a room intended for eggs' incubation. The period of embryo development depends on water temperature and lasts from 5 to 20 days. The kutum larvae should be kept in special baths or on trays. They start feeding on their own at the age of three to five days. In this period the larvae consume green algae and nauplius of Copepoda. Once the larvae start active feeding, they should be transplanted into rearing ponds which are to be filled five to eight days in advance. After 15–25 days, which depends on water temperature, the kutum larvae metamorphose into fry which consume adult forms of Cladocera and insect larvae. After 60 days (from the day of larvae transplantation into the ponds) young kutum attains individual average weight of 1.0 g and they should be released with water from the rearing ponds into the river.
Catching of the common carp spawners should be started in April. The mature spawners should be brought to the fish culture station and released into the spawning ponds. The common carp spawners spawn at water temperature of 16–20°C. Embryo development within the eggs lasts for three to seven days, after which period hatching occurs. Later on, five to seven days after hatching, the larvae of common carp commence to feed actively and then they should be transferred from the spawning ponds into the rearing ponds. The larvae feeding on their own transform into fry which consume Cladocera, Copepoda as well as insect larvae inhabiting the rearing ponds. At the age of one-and-a-half months the young common carp gains an individual average weight of 2.5 g. Then it should be released with water from the ponds into the river.
Once the kutum and common carp's young are released from the rearing ponds, the ponds' bed should be throughly dried up. Subsequently, it could be ploughed and sown with crops.
The process of cultivation of the above-mentioned fishes in the spawning-and-rearing fish culture station will be repeated in the spring of every alternate year.
When breeding the kutum and common carp, the biological techniques and standards worked out in the U.S.S.R. for these species' cultivation at the spawning-and-rearing piscicultural establishments sited in areas climatically and biologically similar to the Mazandaran province can be applied with certain alterations made to fit the local conditions. (See Table 13.) Proceeding from these standards, it is possible to assess the capacity of the prospective spawning-and-rearing fish culture station (See Table 13).
The technical service of the fish culture station can be carried out by seven persons: one skilled fish culturist and six workers.
A piece of land adjoining the Neka river should be surveyed for the establishment of a fish culture station for spawning and rearing of fish. The station should have an area of 100 ha and include eggs incubation division and several ponds for cultivation of kutum, common carp and the Caspian roach.
All expenses on construction and establishment of the fish culture station, as well as its water supply should be borne by the Ministry of Water and Power of Iran (as a compensation of damage which will be done to natural reproduction of the fish).
Management and technical supervision of the fish culture station should be a function of the Ministry of Natural Resources.