Alik Yu. Asanov, Candidate of biological sciences, senior researcher, Volga Research Center of Aquaculture and Aquatic Bioresources, Penza State Agricultural University (30 Botanicheskaya street, Penza, Russia), E-mail: firstname.lastname@example.org
Background. The Surskoye (Penza) reservoir is the largest artificial reservoir of the Sursky Territory (Penza Region, the Republic of Mordovia), the main source of water supply for Penza and Zarechny, the main fishery reservoir with commercial fish stocks, and a recreation site for the population. To prevent “blooming” of the reservoir in 2000, 2002 and 2003 herbivorous fish were brought into the reservoir and algolization with chlorella was carried out. Stocking was carried out in subsequent years, which made it possible to maintain the ecological balance in the reservoir and avoid large-scale “blooming” until 2018. However, in 2018 and 2019, there was a massive development of plankton with concentrations that threaten to cut off the water supply to cities. One of the reasons for the outbreak of plankton numbers is a decrease in the stocks of planktivorous fish in the reservoir due to the fact that predators eat them, since 2011 they have been constantly populated by too small fish. Therefore, the purpose of this work is to assess the effectiveness of preventing the “blooming” of the Surskoe (Penza) reservoir depending on the size of the silver carp stocked with determination of the optimal parameters of its fish stocking material.
Materials and methods. The work used materials on pike perch Sander lucioperca – age composition, size and weight indicators, the share of pike perch ichthyomass from the total fish stock; for silver carp Hypophthalmichthys – the weight of the individual and the volume of fish fry stocked. The materials were obtained as a result of monitoring of aquatic biological resources in the Surskoe reservoir in 2009–2019 and stocking in the period 2000–2019.
Results. In 2000–2006 silver carp was released in the Surskoye reservoir at two years of age weighing 300–400 g, in 2011–2016, 2019 yearlings weighing 15–25 g. The stocks of the main predator of pike perch in the reservoir during this period were at the maximum level, averaging over the past 9 years – 18,3 ± 4,6 % of the total fish stock. A similar indicator in a number of Volga reservoirs, where the loss of silver carp underyearlings from predators reaches 95 %, is 6–9 times lower. That is, underyearlings of silver carp, stocked in the Surskoe reservoir since 2011, having common feeding grounds with pike-perch, are practically completely consumed. The number of older generations of silver carp 2000–2006 due to natural loss and catch has decreased significantly.
Conclusions. The use of silver carp as a melioration fish for preventing the “blooming” of the Surskoye reservoir gave positive results for 17 years. At the same time, a silver carp weighing 300–400 g from fish hatcheries of the Penza region was used for the introduction. Probably, the improvement of the ecological state of the reservoir contributed to a decrease in the mortality of juvenile zander and an increase in its number, due to which the pressure on juvenile fish increased. Therefore, despite the stocking of silver carp under the year in 2011–2019 it was not possible to form the necessary stocks of silver carp of new generations against the background of the decline of the previous ones and to protect the reservoir in 2018, 2019 from the critical mass development of plankton. The recommended sizes of juvenile silver carp, avoiding eating by pike-perch, are individuals weighing more than 200 g, more than 22 cm in length, at the age of two years and older. The use of silver carp from Penza fish hatcheries accelerates their adaptation in the reservoir.
Surskoye (Penza) reservoir, phytoplankton, juveniles of cultivated fish, stocking, silver carp, pike perch
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