Abstract. The paper highlights the prospects of cultivating heat-loving species, such as Australian crayfish and freshwater shrimps in the VI fish breeding zone. Australian crayfish and freshwater shrimps breeding is considered economically attractive for entrepreneurs, having a limited area for farming facilities. At the same time, pond ecosystems require the individual approach and close study in terms of the environmental conditions for the cultivated species upkeeping and the natural forage base that determine the pond biological productivity. Today, there are no clear recommendations on the summer keeping warmwater aquaculture species, in particular, Australian crayfish and freshwater shrimp in the Astrakhan region. To cultivate the new objects of warmwater aquaculture in 2017-2019 the small innovative enterprise Modern Sharapovskiy Fish Breeding Complex researched the production potential of ponds of various categories for receiving marketable products; there was studied the forage base, biomass of zooplankton and zoobenthos satisfying the nutritional needs of farmed objects. As a result of experimental work, it was found that in pond No.2, where freshwater shrimps were grown, there were registered 5 species of Cladocera and 1species of Rotifera, while in pond No.1 used for breeding Australian crayfish there were registered 4 species of Rotifera and only 1 species of Cladocera. Presumably, the observed species composition of the studied ponds is specified by the selectivity of the cultivated objects in zooplankton consumption. The possibility of increasing the bio-productivity of ponds by alternate growing aquaculture and agricultural products has been considered.
The article presents an assessment of the quantitative and qualitative composition of zooplankton in the zoocenosis of the water bodies of Astrakhan. There have been analyzed bioindicators that allow to determine the structure of zooplankton during the research period. A comparative characteristic of the reservoirs has been carried out, according to the indicators of species density (species richness), complexity of the community structure and dominating species. Samples of zooplankton collected in the autumn of 2016 and 2017 in the water bodies within the city limits (the Tsarev river (stations Strelka, Bridge) and the Kutum river (station Strelka opposite the Civil Registry Office and nearby N. Ostrovsky Street) served as the research material. According to the analysis results of biodiversity indices, it has been found that the highest increase in quality indicators (almost doubled in 2017, compared to 2016) was observed in relation to the density of organisms in the Tsarev river. At the same time, the indicator of complexity of the plankton community structure, expressed in quantitative terms, showed an increase by 1.4 times at all stations in 2017, compared to 2016. This is a signal of improvement in the environmental component in urban water bodies. According to the Simpson index values in 2017, plankton species can be assumed to dominate in the zoocenosis. The population of the zoocenosis in the water bodies of Astrakhan is exposed to the anthropogenic impact, which causes changes in the quantitative and qualitative characteristics of communities and their structure. However, increasing values of all three considered biodiversity indices in 2017 indicate a gradual restoration of the biocenosis structure, and an increasing proportion of species in composition of the plankton community.
Today, biological indication methods are recognized as highly effective, since they allow to directly assess the state of the ecosystem and its individual components. Even casual examining of hydrobionts can provide fast and reliable information on water quality. The rivers Kutum and Tsarev located on the territory of the city of Astrakhan were selected as objects of research. Samples of zooplankton collected in the fall of 2016 and 2017 served as research material. Organisms belonging to different zones of saprobity were selected as an indicator group. Calculations of weighted average saprobity were made. Both reservoirs under study have been found to belong to beta-mesosaprobic zone. At station 1 of the Kutum River and at station 1 of the Tsarev River there were registered equal values of the indicator of weighted average saprobity that correspond to oligosaprobic and beta-mesosaprobic zones. This may be explained by the change of community and by the fact that the identified organisms at these stations had a very wide tolerance to polluting factors. At station 2 of the Kutum River in 2016 and 2017 there was stated the predominance and increase in the number of bioindicators of the oligosaprobic zone, while at the other stations the organisms gravitating towards beta-mesosaprobic zone did not seriously change their indicators. As it can be inferred from the results of the saprobiological analysis of the urban watercources (the Kutum River and the Tsarev River), they are undergoing an active process of self-purification, culminating in mineralization of water (beta-mesosaprobic zone) with transition to oligosaprobic zone (almost pure water). However, the presence of indicator organisms and their predominance in plankton samples give grounds to regard the studied water bodies as moderately polluted. That is why it is recommended to lower the recreational load on the urban water bodies by reducing wastewaters discharge from the urban storm sewage system.
Trophological studies of ctenophore Mnemiopsis leidyi conducted in the Caspian Sea more often included species at the later stage of development, as a result, juveniles, metamorphic larvae and larvae were ignored. Ctenophore is known to start feeding since the moment the larva emerges from the egg. Studying the availability of food resources and their size range allowed to trace a certain dependence in the diet of ctenophore, and to determine at which stage of development the jellylike organism in the population feeds most intensively. During the period of naturalization of invasion in the Caspian Sea (1998-2016) there has been registered an increasing number of species with an empty gastrovascular cavity (GVC) in the Mnemiopsis population. According to the analysis results obtained during the study period, the share of individuals with empty GVC in the North Caspian increased to 77.8%, which is associated not with the climatic or hydrological factors, as in 2015 and 2016, but with the availability of food items and internal competition for food resources. There has been found the diversity of the items making food stuff of Mnemiopsis in nature. The main food component is mesozooplankton, as well as meroplankton (cirriped nauplii, larvae of polychaete worms). In food requirements ctenophore does not show selectivity of food resources, the basis of its food make the most available forms of zooplankters.
The article presents a quantitative and qualitative determination of the composition of the plankton zoocenosis reservoirs of the Volga-Akhtuba interfluves. Biological diversity was studied on zootsenotic level using the indices of biodiversity. The comparative characteristic of reservoirs on the above mentioned parameters. Sampling was carried out at the boundary of the conservation Park Volga-Akhtuba interfluves. As the material for this work there were used samples of zooplankton collected in the summer of 2016. Thus, the results of sample analysis detected from 13 up to 19 species of planktonic invertebrates, among which dominated mainly copepod crustaceans ( Eucyclops macruroides ). The dynamics of their abundance and biomass in all the study reservoirs is almost similar, due to the biology of organisms that are dominant in hydrobiocenoses. The calculation of biodiversity indices revealed that the richest were the lakes, where the Margalef index varied from 1.6 to 1.2 units, and the index of Shannon-Weaver, reflecting the complex structure of hydrobiocenosis, had high values (2.97 bits/unit and 2.74 bits/mg). The Simpson index demonstrating dominant position of different species in zooplankton community, was also higher in the lakes. Using selected indicator organisms there were calculated indices of waited average saprobity, according to which water reservoirs of the invironmental park "Volga-Akhtuba interfluves" can be characterized as moderately polluted. i.e., in zooplankton community the leading role belongs to organisms actively participating in the self-cleaning processes of the water reservoir.
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