ECOLOGICAL ANALYSIS OF THE PARASITE FAUNA OF VALUABLE AND COARSE FISH IN THE LOWER REACHES OF THE AMUDARYA DELTA
1Allamuratova Z.B., 2Allamuratov B., 2Allamuratova G.B.
1Nukus branch of Tashkent state agrarian university, Uzbekistan.
2Nukus state pedagogical institute, Uzbekistan.
e-mail: [email protected]
Abstract. The article reveals the results of the study on the ecological characteristics of fish parasites in the lower reaches of the delta of Amudarya river in the Aral Sea region. The dynamics of infestation of young Aral roach in the first year of life with pathogenic parasite Dactylogyrusnanus has been studied in the ecological conditions of Central Asia. Observations of the formation of the parasite fauna of fish in the system of Turtkul pond farm show that for 40 years in the lower reaches of the Amu Darya, the parasite fauna of individual fish has significantly depleted. This is due to a number of abiotic factors: current, fluctuations in the water level, frequent water changes, siltation and other environmental factors that create unfavorable conditions for fish parasites.
The species composition, extensiveness and intensity of fish parasite infestation in Turtkul pond farm system were not the same, which depends both on biotic (species composition, number and stationary distribution of intermediate and definitive hosts of parasites, etc.) and on abiotic (flow rate, gas and salt regime of the reservoir, etc.) factors. The study of the parasite fauna of fish in the systems of Turtkul pond farm is not only of practical, but also of great theoretical importance, since it makes possible to learn the process of formation of the parasite fauna of fish, depending on changes in environmental conditions. Despite the wide distribution in fish D. vastator, the death of young fish from this parasite in Turtkul pond farm was not observed, which we explain by an increase in water salinity in ponds in summer (53.3%) and in winter (26.7%). The infestation of carp with parasites is the weakest, which can be explained by both an increase in water temperature and a decrease in water temperature in winter, and a decrease in the fatness of fish. The main ways in solving the problem of improving the aquatic ecosystems of the region is a monitoring of the state of ecological purity and safety of water reservoirs.
Key words: Amudarya, Southern Aral, region, parasite, fauna, infestation, ecological assessment, ecosystem, ecological factors.
INTRODUCTION
At present, the solution to the problems of hydrochemical changes in aquatic ecosystems has led to an increase in chemical toxicosis of fish, and an increase in the prevalence of parasitic invasions, a decrease in the biological productivity of water ponds, in the ecological purity and sanitary condition of water ponds. Therefore, the main ways in solving the problem of improving the aquatic ecosystems of the region is a monitoring of the state of ecological purity and safety of water reservoirs [11, 16].
Fish industry plays an important role in providing food in the republic, therefore the creation of reservoirs provides good opportunities for increasing the fish supply. However, the regulation of river flow adversely affects the reproduction of some valuable fish species (carp, bream, grass
carp, silver carp, pikeperch, etc.). In this regard, the development of measures aimed at protecting and improving natural spawning becomes important when rearing young marketable valuable fish species in specially created pond farms. The creation of pond and lake farms gives great opportunities for increasing fish production.
The successful management of fish pond and lake farms is often limited by parasitological factors [9]. The operation of such farms showed that their fish farming was often accompanied by massive parasitic diseases and the death of both whitebait and valuable adult fish. Diseases of fish not only disrupt the production activities of pond farms, but with insufficient attention to health-improving measures, these farms can turn into centers of the spread of dangerous fish diseases in pond and lake farms of the Republic.
Aquaculture is currently the fastest growing industry in the world due to its high efficiency and the opportunities to deliver high quality products to markets throughout the year. Recently, the productivity of aquaculture in many countries has increased continually [4, 10]. Fish, like other animals, are susceptible to various diseases. Diseases of fish can occur both in natural water reservoirs and in various fish farms. In natural water reservoirs, diseases often occur with the intense impact of anthropogenic factors on natural ecosystems. With artificial cultivation, diseases more often occur in cases when unfavorable conditions are created for fish farming objects and facilities [4, 10]. Fish are susceptible to invasive diseases, some of which are dangerous to the health of the fish themselves and often cause their mass death, others are dangerous to human and animals that feed on such fish. In addition, invasive diseases sharply reduce the quality of fish products [2, 10]. The spread of parasitic fish diseases is facilitated by various factors, including the use of low-quality feed, violations of fish keeping technology, etc.
[4].
Until now, there is no information on the infection of whitebait with the pathogen Dactylogyrus nanus by one of the representatives of the class of monogenetic flukes, depending on the morphoanatomical features, their behavior on water temperature. Therefore, this article presents the results of the study of dynamics of infection by the pathogenic monogenetic fluke Dactylogyrus nanus of fish Rutilus Aralensis at the first year of life, which are found in water reservoirs of the lower reaches of Amudarya delta. In this regard, the development of measures aimed at protecting and improving natural spawning becomes important when rearing whitebait marketable valuable fish species in specially created pond farms. The creation of pond and lake farms gives great opportunities for increasing fish production.
MATERIALS AND METHODS
According to the data from experts, the bottom fauna of river Amudarya consists of 38 species and forms that belong to 15 systematic groups. Of these, the larvae of chironomids are 8 species and forms, ephemera-7, beetles-6, caddisflies and biting midges -3, the remaining systematic groups are represented in 1 or 2 species. The number of chironomids in the riverbed in the Tuyamuyun region ranges from 6.11 to 83.4%, the biomass from 1.1 to 72.0%, the number of biting midge larvae from 4.4 to 50%, and the biomass from 1.2 to 31.9 %. The total average number of organisms in the studied areas ranges from 6 to 114 specimens, the biomass - from 4.7 to 291.5% mg / m2.
Zooplankton is absent in the channel and branches of the Amudarya River. The backwaters of the culture differ from the channel and branches by the absence of a current, silted soil and high transparency. In this type of adventitious water ponds, zooplankton (cladocerans, copepods) develop well. Many young fish enter the cults and backwaters for feeding. 20 species of fish live in the riverbed in the area of the reservoir. The lakes, located in the zone of influence of the Tuyamuyun reservoir (Turtkul, Kelteminar) are in close connection with the canals and quickly dry up with a decrease in its level. The water of inland water reservoirs has a salinity of the order of 1-5 (8) g / l.
On the territory of the Turtkul district of Kelteminar, the area before used to be 600 hectares, and now it is possible to develop fishing and poultry farming on the lake. The studies were carried out in 2017-2020. The fish were studied from various systems: channal-Yanbosh-yop, 4.6 compartments of ponds, collectors and lakes of the Turtkul pond farm. Thirteen species of fish forms in the amount of 949 specimens were subjected to complete parasitological analysis. To clarify the seasonal dynamics of the parasite fauna of the common carp in Turtkul pond farm, 60 specimens of fish of various ages were examined in spring (March, April), summer (July- August), autumn (September-November), and winter (January-February) during 2017-2019.
The species of fish were determined by the methods of L.S. Berg (1949), Kamilov G.К (1964), Mirabdullaev I.М., Mirzaev U.Т., Khegay V.N.(2001). Processing of collected materials was performed according to accepted parasitological methods of V.А. Dogel (1933), А.P. Markevich (1950), E.М. Lyayman (1966), I.Е.Bykhovskaya-Pavlovskaya (1952,1960) and others.
Along with valuable commercial fish (common carp, carp, bream, pike perch, grass carp, etc.), coarse fish and trash fish were also studied in order to clarify their role while having dangerous parasites. The study of fish and the experiments on parasites were carried out according to the generally accepted method. Measurements were made using an eyepiece of a micrometer, and sketching using an Abbe drawing apparatus. Phase contrast microscopy was used to study mucous sporozoans. The processing of fish in salt, formalin, ammonia baths was carried out according to the method of A.I. Posovsky (1953) and A.K. Sherbinin (1960).
RESULTS AND DISCUSSION
The work of a number of researchers has been devoted to the study of the parasite fauna of fish in the reservoirs of Amudarya river. These works were carried out from 1960 to 1980 of the last century. For example, on the basis of reports and references of S.O. Osmanov (1980), 141 parasite species in fish have been identified in the area of Tuyamuyun water reservoir [9].
Naturally, from 1980 to the present, there have been significant changes in the ichthyoparasite fauna. In Tuyamuyun reservoir, only 55 species of parasites were found in fish. We found that the depletion of the parasite fauna of fish is associated with the depletion of the fauna of aquatic organisms and ecological niches in this region.
The studied area of the lower reaches of the river Amudarya delta in the Aral Sea region is plain, in places elevated over 200 m above sea level. The climate in water reservoir zone is sharply continental, the winter in this area is moderately cold with little snow (the average temperature in January is -50C), the summer is dry (the average July temperature is t = 280C). The sands of the desert in summer heat up to + 700С, in winter there are sometimes significant cold snaps up to - 290С (Dargan-Ata). The average annual rainfall is 100 mm per year (Dargan-Ata). Gray-brown,
fine-grained stony soils are widespread here, there are also takyrs (bare), and bog soils and salt deposits are found in the tracts. In areas somewhat distant from the riverbed, fixed sands come across. Near the river bed, there are significant areas occupied by alluvial, boggy floodplain, culturally irrigated soils, meadow gray soils.
In total, 55 species of parasites were found in the studied fish, including 29 species in fish in Yanbosh-yop channel, 55 species in ponds of 4.6 divisions, 23 species in collectors, 13 species in Turtkul lakes and 11 species in Kelteminar lakes. In a systematic respect, the identified parasites belong to 13 classes and forms:
1) Flagellata (6 species), 2) Sarcodina (1),
3) Sporozoa (1 ), 4) Cnidosporidial (3), 5) Microsporidia (1), 6) Cilita (30),
7) Dermocyptium (1), 8) Monogenoidea (19), 9) Cestoidea (2), 10) Trematoidea (1), 11) Nematoda (1), 12) Hirudinea (1), 13) Crustacea (3) species.
Among the parasites discovered, the most diverse species composition is characterized by the class of monogenetic flukes (19 species were found). It is mainly represented by specific species, and only some Dactylogyrus vastator, D. anchoratus and some others were found in 2 hosts. The most numerous were the pathogenic genera Dactylogyrus (19 species). Of the protozoa, the most numerous in terms of species were parasitic ciliates - 20 species, of which the genus Trichodina (10 species).
Most of the parasites we found are common in fresh water reservoirs of Uzbekistan. A number of species are indicated for the first time for the reservoirs of Central Asia (Hemiophrus branchiarum, Scyphidia doneccae, Apiosoma baninae). For Bothriocephalus opsarichtydis, previously unknown final hosts have been established (Pseudorasbora parva, common hemiculter, Amur bitterling).
Among the detected parasites there are species known as causative agents of dangerous fish diseases both in ponds and in natural reservoirs. They are costia necatrix, Eimeria carpelli, Glugea luciopereae, Myxobolus muelleri. M.pfeiferi, M.cyprini, Ichtyophthirius multifiliis, Apiosoma carpelli, Trichodina nigra, Dactylogyrus vastator, D. extensus, Gyrodactylus elegans, Bothriocephalus opsarichthydis, Ligula intestinalis, Diplostomum spathaceum, Piscicola geometra, Argulus foliaceus , etc.
Most of the parasites found in fish from Turtkul pond farm were also found in fish from Yanbosh-yop channel. In a place with water, fish and intermediate hosts, they can penetrate into ponds, which must be taken into account to improve their health when carrying out fish breeding and sanitary activities.
During the period of our research (2009-2019) in the ponds of Turtkul stationary fishery farm, we studied the dynamics of infestation of whitebait Aral roach in the first year of life, pathogenic with the parasite Dactylogyrusnanus, in the ecological conditions of Central Asia.
It was found that the extent of infection was 8.0%, in the pre-larva on days 1-5, on April 1-5, the intensity of invasion was 1-1 specimens, and on 28-30 June at 90 days of age, the extent of infection increased by 68%, the intensity of invasion was 1– 21 specimens, then on December 28-30, extensiveness was 12.0%, intensity of invasion 1-8 specimens, on 20-30 January, the extent of infestation of whitebait roach decreased to 8.0%, intensity 1-3 specimens, in February, the extent of infection of the whitebait roach of this year of life with the pathogenic parasite D.
nanus decreased to 4.0%, the intensity to 1-1 specimen, on March 28-30, in 2019, the extent of infection of whitebait Aral roach of 13 months (1+) was 30.0 %, intensity 1-15 specimens. Of 949 specimens of the investigated fish, 350 specimens of 13 species and forms of fish were found to be infected. In particular, in the ponds of 4.6 division, 63.1% of the studied fish were infected, in Yanbosh-yop channel -22.6% infected, in the collector-26.7%, in the lakes: Turtkul- 36.0% and Kelteminar-8.0 %.
The total parasite infestation was noted in such fish as common carp (20.0-86.7%), carp (20.0- 60.0%), Turkestan barbel (30.8-85.0%), Aral roach (20.0 -86.7%), Aral bream (10.0-81.0%), grass carp (26.6-83.3%), Prussian carp (16.7-60.0%), catfish (13, 3-61.1%), pike perch (18.4- 61.1%), silver carp (20.0-60.0), bighead carp (15.4-37.5%). The fauna of parasites was less diverse in Amur topmouth gudgeon (12.3-33.3%), common sharpbelly (13.3-40.0%), Amur bitterling (13.3-46.7%).
The species composition, extensiveness and intensity of fish parasite infestation in Turtkul pond farm system were not the same, which depends both on biotic (species composition, number and stationary distribution of intermediate and definitive hosts of parasites, etc.) and on abiotic (flow rate, gas and salt regime of the reservoir, etc.) factors. The study of the parasite fauna of fish in the systems of Turtkul pond farm is not only of practical, but also of great theoretical importance, since it makes possible to learn the process of formation of the parasite fauna of fish, depending on changes in environmental conditions.
Especially, great changes have occurred in the fauna of the carp and some other fish species.
Carp is one of the most valuable commercial fish in Amudarya ponds and in the systems of the Turtkul pond farm. In different water reservoirs of the farm and in different seasons, 75 specimens of carp were examined, including 15 specimens in Yanbosh-yop, in 4.6 divisions of ponds - 15, in collectors - 15, in lakes Turtkul-15, Kelteminar-15 specimens. Of the 14 species of parasites found in carp (20-86.7%), infection of 4.6 ponds on the farm are the most common pathogens in Eimeriacarpelli- (13,3-53,3%), Jchthyophthiriusmultifiliis-(13,3-60,0%), Apiosomapiscicolum- (73,3),Trichodinanigra-(26,7-66,7%), Dactylogyrusvastator-(6,7-80,0%), D.extensus-(6,7-53,3%), Bothriocephalusopsarichthydis-(20,0-53,3%), etc. Species composition, the extensiveness and intensity of parasitic carp infestation in Yanbosh-yop channel, collectors, lakes were not the same, it depends both on biotic and abiotic (flow rate, water turbidity, gas and salt regime of reservoirs, etc.) factors. (fig.1).
Figure 1. Dynamics of seasonal infection of whitebait in the conditions of Turtkul pond farm in the Southern Aral Sea region
In general, the observations of the formation of the parasite fauna of fish in the system of Turtkul pond farm show that for 40 years in the lower reaches of the Amu Darya, the parasite fauna of individual fish has significantly depleted. This is due to a number of abiotic factors: current, fluctuations in the water level, frequent water changes, siltation and other environmental factors that create unfavorable conditions for fish parasites [11, 16].
Elucidation of seasonal changes in the parasite fauna makes it possible to gain a deeper understanding of the biology of parasites, to establish the periods of their greatest activity and increase in numbers, and therefore the periods of greatest danger for fish in a given geographic zone. This is important for planning sanitary activities [12, 14, 19, 25].
In spring and autumn, the infestation of the fish Eimeriacarpelli increases, which makes 66,7%
and 60,0% respectively, Ichthyophthyiriusmultifiliis - 73,3% and 60,0%, Dactylogyrusvastator - 66,7% and 53,3%, Gyrodactyluselegans - 46,7% and 33,3%, Bothriocephalusopsarichthydis - 40,0% and 26,7%. In autumn the carp got infected at 73,3%, while in winter 26,7% (fig.2).
66.7
73.3
66.7
46.7
40
73.3
60 60
53.3
33.3
26.7 26.7
0 10 20 30 40 50 60 70 80
parasitic fauna infestation %
in the spring in the fall
Figure 2. The number of total fish parasite infestations in Turtkul pond farm in the Southern Aral Sea region
Despite the wide distribution of D. vastator in fish, the death of whitebaits from this parasite in Turtkul pond farm was not observed, which we explain by an increase in water salinity in ponds in summer (53.3%) and in winter (26.7%). The infestation of carp with parasites is the weakest, which can be explained by both an increase in water temperature and a decrease in water temperature in winter, and a decrease in the fatness of fish. The existing practice of controlling fish diseases suffers from some one-sidedness, since the whole complex of measures aimed at breaking the epizootic chain is not used [18, 22]. Long-term rearing of whitebaits (4-5 months), sometimes lack of feed in certain periods of rearing, long descent and fishing in the ponds, accompanied by traumatization of fish, sometimes lack of flow in nursery ponds create condition for the occurrence of diseases and determine the specifics of health measures. Under these conditions, in order to prevent mass fish diseases, a set of measures is required aimed at all links of the "parasite-host-external environment" system based on knowledge of the specific parasitological situation. [15, 17, 21, 24, 26].
The fish diseases controlling measures should be aimed, first of all, at preventing the pathogen in the reservoir or suppressing its number, strengthening the defenses of the host organism, creating conditions that prevent the development of diseases. Conventionally, control measures can be divided into general, special and organizational.
General measures to control fish diseases include adequate feeding of fish and the creation of a rich natural food base, high-quality fish farming, keeping ponds in a good sanitary and fish- breeding condition, control of trash "extraneous" fish, avoiding excessive fish stocking densities near ponds, combating intermediate and definitive hosts of parasites (mollusks, fish-eating birds, etc.), reduction of trauma during fishing ponds and fish transplantation, reduction of the time for rearing whitebaits on farms, constant monitoring of the food supply and hydrochemical regime, as well as the state of fish, etc.
0 10 20 30 40 50 60 70 80 90
20 20
30.8 20
10
26.6
16.7
13.3 18.4 20
15.4 86.7
60
85 86.7
81 83.3
60 61.1 61.1 60
37.5
parasitic fauna infestation %
min max
Most of these measures are necessary elements of intensification and, in addition to disease prevention, are aimed at increasing fish productivity [15, 18, 20].
Special control measures are aimed at eliminating (or suppressing the number) individual pathogens by using special means and methods, increasing the general and specific resistance of fish, creating conditions that prevent the development of diseases. The use of special measures does not exclude combating fish diseases, but on the contrary requires complete adherence to general preventive measures. In the practice of fisheries, this is often not taken into account and with the help of some means they try to improve the health of the farm. This may not lead to the desired result. By applying a set of measures aimed simultaneously at several links of the
"parasite-host-external environment" system, it is possible to more effectively control fish diseases [11, 14].
CONCLUSION
To prevent invasive diseases of whitebaits of one-year-olds and two-year-olds (ichthyophthyroidism, amiosomiasis, trichodinosis, dactylogyrosis, gyrodactylosis) with remedies, the antiparasitic baths of 6-7% sodium chloride solution lasting 6 minutes, formalin in baths 1: 2500 at exposures of 4-6 minutes can be recommended before transferring fish in wintering ponds and back to feeding ponds. It is advisable to process fish in our conditions in autumn and spring in order to provide the best conditions for wintering of fish.
Controlling fish diseases in such complex fish farms as Turtkul pond farm, requires a number of organizational measures. This is, first of all, the availability of qualified personnel, the preparation of annual, seasonal plans for sanitary activities, taking into account and recording the effectiveness and efficiency of the applied control measures, etc.
Some pathogenic species of fish parasite fauna of the Turtkul pond farm multiply rapidly in ponds and under certain conditions, they cause serious diseases and even death of fish (Сryptobiacyprini, Ichthyophthiriusmultifiliis, Dactylogyrusvastator, D. extensus, Ligulaintestinalis, Gyrodactyluseleganus, Bothriocephalusopsarichthydis, Diplostomumspathaceum, Lerneacypinacea and etc.). We have briefly described the role of parasites that were widespread during the period of our study. Therefore, in our conditions, when drawing up projects for fish farms, the specialists in fish diseases from research institutes and the state veterinary service of the Republic of Karakalpakstan and Uzbekistan should be involved.
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