Pastoral aquaculture in the reservoirs of the Kuban basin

The article provides calculations and recommendations for fisheries development and improvement of fish productivity of reservoirs in the Kuban basin. The taxonomic composition of water biological resources has been studied and the natural bio-production potential of some reservoirs in the South of Russia has been determined. It is proposed for the purpose of pastoral aquaculture to produce directed formation of the ichthyofauna of reservoirs by yearlings Hypophthalmichthys molitrix, Hypophthalmichthys nobilis, Ctenopharyngodon idella, and as anaddition Cyprinus carpio, Mylopharyngodon piceus, Liza haematocheila with an individual mass not less than 25-30 g, which will allow rational use of forage resources of aquatic ecosystems.


Introduction
In the Kuban basin, there are more than 15 reservoirs located on the territory of four southern regions of the Russian Federation: the Karachay-Cherkess Republic, Stavropol territory, Krasnodar territory and the Republic of Adygea.
In the Krasnodar territory there are 3 reservoirs with a total area of 47.9 thousand ha, including Krasnodar area of 40 thousand hectares -pond two regions (Krasnodar Krai and Adygeya Republic); Kryukovskaya area of 4 hectares and Varnavinsky -3,9 thousand hectares of the Reservoir, as pasture reservoirs are operated very inefficiently. In recent years, the catch in reservoirs has decreased by 5.6 times compared to the beginning of the 90 -ies of the last century, while herbivorous species that make up more than 65% of the catches have not been found in catches since 2001. Currently, the fishery is based mainly on low-value fish species (Pelecus cultratus, Carassius auratus, Rutilus rutilus, Blicca bjoerkna, etc.). The reasons for the inefficient use of reservoirs as pasture reservoirs are insufficient volumes of stocking them with fish-planting material of herbivorous species, low efficiency of fishing, as well as unrecorded catch.
The varnavinskoye reservoir was created in 1971 on the Varnavinskiye plavniks, located in the left-Bank floodplain of the Kuban river, 10 km North-East of Krymsk, Krasnodar territory. The area of the reservoir at the NPU is 3900 ha, the volume is 40 million m 3 .
Of many rivers (Abin, Second, Adagum, And Heceptin, Khobza, Kudako, Nepal, Psif, Sebas, Schuch), conditionally related to the river system, Varnavinsky reservoir, reservoir flow Abin, And, Second, the Adagum. The Abin river is the largest and most water -rich: its length is 81 km, its catchment area is 450 km2, and the average long-term annual flow is 207 million L3. The other rivers are much smaller. The water resources of the rivers of the Varnavinsky reservoir system are used mainly for agricultural purposes, they are included in the Varnavinsky and Fedorovsky rice systems. The water of the Varnavinsky reservoir belongs to the second type of hydrocarbonate-calcium group (mineralization-0.44-0.65 g / l, hardness-4.40-6.68 mg-EQ/l, alkalinity-3.25-4.58 mg-EQ/l).
The main ions are NSOs-and Ca2+, which determine the carbonate equilibrium. Active reaction of water pH of 7,5-8,6. The content of biogenic elements varies: nitrogen-1.34-1.91 mg / l, phosphorus-0.12-0.36 mg / l. Thus, the hydrological and hydrochemical regimes of reservoirs in the Kuban basin are generally satisfactory and do not interfere with pastoral fish farming.
The microflora of the Krasnodar reservoir is characterized by seasonal dynamics, and there is a direct dependence of population accumulation on water temperature. The correlation coefficient is 0.701.
In winter, environmental conditions, especially low water temperatures and short daylight hours, determine the small number of phytoplankton, which is about 3.1 % of the annual amount. In the following months, there is an increase in the mass of algae, reaching the highest number in July -42.9 %, then there is a gradual decrease in the number.
In winter and in the early spring, diatomeae (Diatomeae) prevail among the microalgae of the reservoir in terms of number and biomass. Mass development at this time is achieved by representatives of the genera Cyclotella, Melosira, and Naricula. Protococcal (Protococcophyceae), blue-green (Cyanobacteria), euglenic (Euglenoidea), volvocaceae and other groups of microflora in winter plankton are very poorly represented.
The value of Protococcophyceae in the reservoir increases from winter to autumn. During the year, they are represented by small forms of the genus Chlorella, Ankistrodesinus, their number is significant-50-5208 thousand copies/m 3 , but their primary role in plankton is periodically obscured by the predominance of Cyanobacteria (the most widespread of them are Merismopedia punctata, Anabaenopsis Elenkinii, Oscillatoria limnetica).
The horizontal distribution of phytoplanktin in the reservoir is uneven, the most productive microflora is the dam site and the left-Bank shallow zone between the mouths of rivers such as Psekups and przysz. The tiered distribution of the taxonomic composition and biomass of lower algae also has certain regularities. Lowering the water temperature and reducing the amount of sunlight with increasing depth, make the environment for these organisms less attractive. As a rule, with increasing depth, the biomass and number of suspended plant organisms decreases, and the taxonomic composition becomes much poorer. The most preferred for the development of phytoplankton is the upper part (0.5 m) of the water column of the reservoir, at a depth of about 2 meters, its biomass is reduced by almost half. At depths of about 5 meters, the average phytoplankton biomass is just over 30 % of that recorded at the upper level.
Over the entire observation period, including active vegetation and relative rest in the cold season, the average values of biomass of lower plant organisms in the water column varied from 1.17 to 18.2 g / m 3 .
In addition to typical planktonic forms, larvae of bugs of the genus Corixa, mosquitoes of the family Chironomidae, larvae of beetles of the genus Dytiscus, representatives of the subclass Oligochaeta, class Ostracoda and type Nematoda were found in significant numbers in zooplankton. Observations of the seasonal dynamics of zooplankton in the period from April to September showed that it is characterized by a pronounced periodicity.
In spring, the reservoir maintains a river regime, which is why rotifers (Rotatoria) predominate in the zooplankton (115 thousand ex/m 3 ), accounting for 85% of the total number of organisms; the average zooplankton biomass during this period is low -0.59 g/m 3 , with fluctuations from 0.20 to 1.27 g/m 3 .
In the summer, when the water temperature increases, there are significant changes in the development of zooplankton in quantitative and qualitative terms: rotifers (Rotatoria) are significantly inferior to lower crustaceans (Entomostraca). Values are averages of biomass of zooplankton in reservoirs in spring and summer hesitate from 0.88 g/cm 3 to 1.58 g/m 3 , which is associated with a predominance of larval and copepodite crustaceans in summer. The highest values of zooplankton biomass in the reservoir were observed in the autumn period (up to 2.85 g / m 3 ).
Significant changes in the development of zooplankton occur both by season and in different parts of the reservoir. So, in the river section, where the strongest currents and a large number of suspensions were observed, zooplankton had the lowest biomass indicators during the entire growing season. Only in summer, with a decrease in the flow rate, it reaches a maximum of development-2.36-3.98 g / m 3 .
The zooplankton biomass in the upper section is also small: in the spring 0.14-0.97 g / m 3 , in the summer-up to 1.31 g / m 3 ; rotifers and oar-legged crustaceans predominate. In autumn, this section of the reservoir is drained and filled again only in April-March.
In the Central section of the reservoir, zooplankton biomass varies slightly from 1.95 to 2.45 g / m 3 .
Zooplankton biomass ranges from 0.16 to 8.18 g / m 3 in the near-dam section.
The lowest numbers and biomass of zoobenthos were found in former riverbeds, deep areas along the dam, and in the Central zone. The greatest number and biomass of bottom fauna during the entire growing season are observed in shallow areas of the left Bank of the reservoir with sparse shrubby thickets and coastal aquatic vegetation; the fauna was represented mainly by Oligochaeta, detritus-eating and predatory larvae of chironomids (Chironomidae).
Macrophytes in the reservoir is currently concentrated in the coastal shallow areas, they are significantly developed at the mouths of the rivers Psekups and Pshish. Amphibian buckwheat (Polygonum amphibium) forms the largest areas of overgrowth in the reservoir and is distributed to a depth of 6 m.previously existing associations of Phragmítes Australis, Bolboschoenus sp. both the angustifolia Turkha are in a depressed state due to a significant increase in the water level.
The zoobenthos includes representatives of the 5 groups of benthic organisms. The species composition of zoobenthos includes 31 species.

Kryukov reservoir
Feed resources (phytoplankton, zooplankton, zoobenthos) of the Kryukov reservoir are developing well. Thus, the phytoplankton biomass varies in the spring period from 0.83 to 4.86 mg / l (the summer phytoplankton biomass reaches 26.3 g / m 3 ). The average for the growing season is 18.6 g / l 3 .

Varnavinsky reservoir
Feed resources (phytoplankton, zooplankton and zoobenthos) of the Varnavinsky reservoir are developing satisfactorily.
Phytoplankton is represented by 112 taxa belonging to 9 groups. The most diverse in taxonomic terms are protococcal algae (Protococcophyceae) -49 species. An equal number of 15 species were represented by blue-green (Cyanobacteria) and diatomaceous (Diatomeae). Relatively less diversity was characterized by Volvocaceae (Volvocaceae) -8 species, desmidiales (Desmidiales) -6 species, euglenoidea (Euglenoidea) -11 species and pyrophyta (Pyrrophyta) -4 species. The minimum number of 2 species was represented by yellow-green (Xanthophyta) and Golden (Chrysophyta) algae. Phytoplankton biomass ranges from 0.88 to 4.86 g/m 3 in spring, and summer phytoplankton biomass reaches 24.8 g / m 3 . On average, during the growing season, the biomass of phytoplankton in the Varnavinsky reservoir is 13.9 g / m 3 .
The zooplankton of the reservoir is represented by three typical planktonic groups of organisms: oar-footed (Copepoda) and branch-billed (Cladocera) crustaceans and rotifers (Rotatoria).
The dynamics of zooplankton biomass for the entire growing season (April-October) has the form of a curve with two vertices. The maximum values of zooplankton biomass in the reservoir were recorded in the spring period (April-may) and ranged from 3.8 to 5.6 g / m 3 . In the summer, with the establishment of high water temperatures, there is a sharp decline (0.5-0.8 g / m 3 ), which is due to the biological characteristics of some species of branched crustaceans (Cladocera). By mid-September, when the water temperature approaches optimal values and the gas composition is normalized, the zooplankton biomass begins to grow again, reaching 1.6 g / m 3 . Thus, during the growing season, changes occur in the dominant number and biomass of taxa, in this connection, the number of zooplankton organisms ranges from 12 to 320 thousand copies/m3, and their biomass -from 0.5 to 5.6 g / m 3 , making an average for the observation period-2.3 g / m 3 .
Zoobenthos. Organisms representing the EPI-and infauna of the bottom communities of the reservoir belong to the following groups of organisms: chironomid larvae (Chironomidae), Oligochaeta (Oligochaeta), beetle larvae (Dytiscus), mysida (Mysida), Gammaridae (Gammaridae)). The larvae of chironomids (Chironomidae) dominate, the biomass of which varied from 0.4 to 3.5 g/m 2 during different observation periods. On average, during the growing season, the total biomass of invertebrate organisms inhabiting benthic communities is 1.89 g / m 2 .
According to the level of development of forage organisms, the Kryukov and Varnavinsky reservoirs are medium-sized reservoirs.

Krasnodar reservoir
The formation of the ichthyofauna of artificial reservoirs of complex purpose has a number of General regularities. The ichthyofauna of the Krasnodar reservoir formed at the expense of fishes that lived before in Texcom reservoir, fish the middle and lower reaches of the river Kuban and its left-Bank tributaries: the rivers Laba, Belaya, Pshish, Psekups, etc. Various sources note the great diversity of the fish fauna of the basin of the Kuban river, with more than 79 species and subspecies of fish, of which 36 are constantly encountered in the reservoir, and 43 species and subspecies occur sporadically at different times of the year [5,6,7]. They include marine, pass-through and semi-passable fish (Beluga (Huso huso), sevruga (Acipenser stellatus), russian sturgeon (Acipenser gueldenstaedti), black sea shad (Alosa maeotica), black sea sprat (sprat) (Clupeonella cultriventris), three-legged stickleback (Gasterosteus aculeatus), and Common percarina (Percarina demidoffi), donets ruffe (Gymnocephalus acerinus), European anchovy (Engraulis encrasicholus) and some types of gobies), which found favorable conditions for reproduction both in the reservoir bowl and in the rivers that flow into it, as well as some universes -sturgeon (Acipenser ruthenus), american paddlefish (Polyodon spathula), smallmouth buffalo (Ictiobus bubalus), grass carp (Ctenopharyngodon idella), black carp (Mylopharyngodon piceus), channel catfish (Ictalurus punctatus), silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis).
According to the nature of reproduction, the ichthyofauna of the Krasnodar reservoir is divided into 5 ecological groups. The most widely represented phytophilic ecological group includes 17 species and subspecies of fish. Lithophilic ecological group -6 species, psammophilic-8 species, pelagophilic-4 species, gestating-2 species of fish.
According to the terms of spawning, the main part of the fish species of the Krasnodar reservoir belongs to the spring-spawning and spring-summer ones. However, the timing of fish spawning in the Krasnodar reservoir is not constant and depends on spawning temperatures and water level regime. Almost every year, due to a sharp discharge of water on the farm, the beginning spawning course of fish to spawning grounds is interrupted three times, and sometimes the spawning of fish. In this regard, the spawning efficiency of the main commercial fish species is extremely low.
The systematization of fish in the Krasnodar reservoir by the nature of food is complicated by the fact that the main part of the species feeds on a variety of forage organisms. It is difficult to identify the dominant food item. The main part of the species is peaceful, and only 6 species (Sander lucioperca, Sander volgensis, Perca fluviatilis, Silurus glanis, Esox lucius, Aspius aspius) are predatory. Peaceful fish in the diet are divided into the following groups and subgroups: herbivorous -fitoplanktona (Hypophthalmichthys molitrix), macropelopia (Ctenopharyngodon idella), purificatory (Chondrostoma nasus); animal-eaters -zooplantophages (Chalcalburnus chalcoides schischkovi, Alburnus alburnus, Leucaspius delineatus, Pelecus cultratus, Hypophthalmichthys nobilis), zoobentophages (Cyprinus carpio, Abramis brama, Blicca bjoerkna, etc.); detritosdetritophages (Carassius carassius). However, when analyzing the range of fish nutrition in the Krasnodar reservoir, we can trace the multicomponent composition of their food and the existing species composition of fish, which masters almost all the food niches of the reservoir. The basis of the diet of predatory fish is mainly small low-value species.
Thus, the ichthyofauna of the Krasnodar reservoir and rivers flowing into it are represented by 36 species of fish that live permanently and 43 species that come in for spawning or short-term feeding. However, the fishery is based on 5-8 species of fish (Cyprinus carpio, Abramis brama, Sander lucioperca, Pelecus cultratus, Carassius auratus, Blicca bjoerkna, Rutilus rutilus).
The nature of power in the ichthyofauna is represented by 5 groups: fitoplancton, phytophages, zooplanktivore, benthophage and prey, among which the most numerous are zooplanktonic and bentofag.
The formation of the fish fauna occurs mainly in a natural way. This led to the formation of populations of low-value fish species (Scardinius erythrophthalmus, Rutilus rutilus, Perca fluviatilis, Leucaspius delineatus, etc.), which currently occupy the first place in both numbers and ichthyomass. Directed formation of the ichthyofauna of the Kryukovsky reservoir has been going on for a long time, but the introduction of valuable fish species into the reservoir is carried out in insufficient numbers. In addition, the issue of conducting fishery reclamation measures aimed at reducing the number of weedy and lowvalue fish species that act as trophic competitors to commercial species is acute. Valuable fish species (Cyprinus carpio, Abramis brama, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis, Ctenopharyngodon idella, Sander lucioperca, Mylopharyngodon piceus) are characterized by high biological indicators, but their number is insignificant.
The process of formation of the ichthyofauna is mostly completed and now the reservoir is inhabited by both representatives of the native ichthyofauna and acclimatisers. The largest number is created by low-value fish species, the number of valuable species is relatively small. Natural reproduction, due to abiotic factors (reservoir filling and drainage, temperature, weather conditions, etc.), is difficult and its efficiency is low.
The efficiency of natural reproduction depends entirely on the level, temperature, and wind conditions of the reservoir. High water content in the spring period is later replaced by a sharp decrease in incoming water, which leads to limited areas of spawning grounds and feeding of young. Ultimately, this determines the weak efficiency of natural reproduction of phytophiles.
In the most unfavorable environmental conditions, Cyprinus carpio is very sensitive to changes in abiotic factors and the quality of spawning grounds. However, despite the relative plasticity of other fish species (Abramis brama, Rutilus rutilus) in the selection of spawning substrate and spawning sites, high efficiency in their reproduction is not observed. Violation of gradual warming and falling water levels, combined with rainy and windy weather, inhibits the participation of producers in spawning, leads to drying out of spawning grounds and disruption of the reproductive process of females. The resulting generations of fish are very small and a significant increase in commercial stocks, except for Carassius auratus, is not expected.
To increase the efficiency of natural reproduction of valuable fish species, it is necessary to carry out a number of fish-breeding and reclamation measures, which should include the installation of artificial spawning grounds, stocking with valuable fish species, as well as an agreed schedule of water intake for agriculture, taking into account the fisheries.
The fish that live in the Varnavinsky reservoir do not differ significantly in biological data from the fish of the Kryukovsky reservoir. Fish spawning begins at the same time, the terms of maturation of carp, bream, pike perch coincide, the fertility of females of the Varnavinsky reservoir is the same as in Kryukovsky. The range of nutrition and the rate of linear and weight growth of carp, bream, walleye and herbivorous fish in both reservoirs is the same.
Thus, despite the small size of the Varnavinsky reservoir, it is of fishery importance and requires fish-breeding and reclamation activities, since the native ichthyofauna will not be able to provide high fish productivity.
Studies conducted on reservoirs in the Kuban basin have shown that the Krasnodar reservoir is the most rich in species, with 79 taxa. The species composition of the ichthyofauna of the Kryukovsky and Varnavinsky reservoirs includes 23 and 27 species, respectively.
The ichthyofauna of the reservoirs of the Kuban basin (mainly Krasnodar) is constantly replenished with new species from remote ecosystems as a result of fish-breeding and acclimatization works and hydrostructure. To date, there are more than 38 species (Pseudorasbora parva, Rhodeus amarus, Ictalurus punctatus, Ctenopharyngodon idella, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis, Oryzias latipes, Cobitis melanoleuca, Neogobius syrman, etc.). It should be noted that the ichthyofauna of the Kuban river basin has been replenished with a significant number of new species, including naturalized due to introductions (7 species), self-dispersing (5 species) and expanded ranges (18 species).
Along with this, the ichthyofauna of reservoirs in the Kuban basin is represented by a significant number of endemic forms (Chondrostoma colchicum kubanicum, Barbus tauricus kubanicus, Leuciscus aphipsi, Alburnoides kubanicus, Romanogobio pentatrichus, Sabanejewia kubanica, etc.). Thus, the current composition of the ichthyofauna of the reservoirs of the Kuban river basin is represented by 79 species of fish, among which there are both mass ubiquitous and single-occurring tuvodnye, semi-passable, passable, acclimatized and self-acclimatized species [8,9].
Methods for increasing fish productivity of reservoirs of pasture aquaculture in the Kuban basin Studies have shown that forage resources (phytoplankton, zooplankton, zoobenthos, macrophytes) of reservoirs are developing quite well. The average seasonal biomass of phytoplankton in reservoirs ranges from 13.9 g / m 3 (Varnavinsk reservoir) to 18.6 g / m 3 (Kryukov reservoir), zooplankton from 2.3 g / m 3 (Varnavinsk reservoir to 4.52 g / m 3 (Krasnodar reservoir), zoobenthos from 1.89 g/m 2 (Varnavinsk reservoir) to 2.86 g/m 2 (Krasnodar reservoir). However, feed organisms mainly use low-value, low-growth fish species that produce low-quality fish products. Phytoplankton and macrophytes are hardly used by local fish species.
Climatic conditions cause a high bio-production capacity of reservoirs in the southern region. However, without carrying out work on constructive regulation of the species composition and number of individual fish species in reservoirs, their actual fish productivity becomes significantly lower than the potential [10][11][12][13][14][15][16]. When determining the potential fish productivity of pasture aquaculture reservoirs, we used the following P / V coefficients for more reliable calculations: for phytoplankton -45, for zooplankton -15, for zoobenthos -6, for macrophytes -1.1. The obtained data on the production of phytoplankton, zooplankton, zoobenthos and macrophytes are indicative, but they can be used to directly determine the potential fish productivity of reservoirs (table.1). In order to achieve the calculated indicators of fish productivity of reservoirs in the Kuban basin, it is necessary to carry out a set of reclamation works to reduce the number of low-value and predatory fish species. The basis of commercial ichthyofauna should be valuable fast-growing species. In this regard, to ensure the achievement of the planned indicators of the commercial yield of fish stocking of reservoirs is advantageously carried out with fingerlings (Ctenopharyngodon idella, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis) and extension: Cyprinus carpio, Mylopharyngodon piceus, Liza haematocheila, etc.) individual weight below 25-30 g, at the rate of 250 ind/ha white silver carp, 100 ind/ha bighead carp, and 50 ind./ha grass carp, 30 ind./ha carp-carp. In the third year after stocking, when the fish reach an individual weight of 2.0-2.5 kg and when leaving the fish landing 15-25%, the fish productivity of the Krasnodar reservoir will be 195 kg/ha, the Kryukovsky reservoir -168 kg/ha, and the Varnavinsky reservoir-192 kg/ha.in addition, local fish can give up to 5 kg / ha of fish products. In total, the fish productivity of reservoirs can reach about 200 kg / ha. Currently, the catch is based on lowvalue fish species (Carassius auratus, Pelecus cultratus, Blicca bjoerkna, Rutilus rutilus, Scardinius erythrophthalmus, etc.), the fish productivity is 2-5 kg/ha. Thus, the reservoirs of the Kuban basin are quite suitable for growing commercial fish by pasture type. When conducting fish-breeding and reclamation works on reservoirs and stocking them with valuable fast-growing fish species, the fish productivity can reach 170-200 kg/ha.