Reproductive characteristics of the introduced species ― Eastern freshwater shrimps (Macrobrachium nipponense de Haan, 1849) in the lower Dnister river

Purpose. To study reproductive characteristics of female freshwater shrimp M. nipponense (Dniester population) in natural and artificial conditions. Methodology. Field studies were carried out from April to October 2016-2019 in the Kuchurgan and Dniester lagoons, fish ponds and lakes of the lower Dniester and Turunchuk rivers. Shrimp were caught in coastal areas with net and special traps using a bait (ground silverside). The studies were conducted in the field and laboratory conditions. For experimental work, the caught shrimp was transported to the aquarium department of aquatic biological resources and aquaculture of Odessa State Ecological University. For the cultivation and reproduction of shrimp, 0.3 m³ glass aquariums were used, combined in an experimental setup with a recirculating aquaculture system (RAS) with a total working volume of 1.2 m³. During the experiment, the conditions were close to the environment, where shrimp were caught. During the biological analysis of the shrimp, following parameters were determined: sex, total length and body weight (stage and duration of embryogenesis). The survival of M. nipponense under various conditions was also recorded. Following modern instruments were used for the express analysis of hydrochemical parameters of the environment: ECOTEST -2000 T (О2; NO-2; NO-3; NH-4; CO2; phosphates, pH), Azha-101M thermooximeter (Т, оС; О2), pH meter-150 m); ATAGO-100 refractometer (salinity and water density). Saline solution, in special experiments, was produced in laboratory conditions by diluting seawater. Findings. Fertilized shrimp eggs have an oval shape, and their average sizes varied within 0.58-0.66 mm (length) and 0.39-0.46 mm (width). It was found that the size of fertilized eggs in M. nipponense of the Dniester population differed in size in various natural waters. The largest sizes (0.66 ± 0.035 and 0.46 ± 0.014 mm) and an average volume of 0.073 mm3 were observed in shrimp eggs from the Kuchurgan estuary. These parameters significantly (P≥0.95) differed from shrimps from the Dniester estuary, which had the smallest sizes (0.58 ± 0.022 and 0.39 ± 0.011 mm) and average volume (0.046 mm3). Shrimp from ponds and lakes of the Dniester and Turunchuk had average size and egg volume, which, according to these parameters, did not significantly differ from those of individuals from the Kuchurgan and Dniester estuaries. An analysis of shrimp fertility of the Dniester population showed that the IRF and FRF increase in direct proportion to the increase in the size and weight of females that is natural for all poikilothermic animals. IRF in the linear size range of female M. nipponense from the Dniester population of 2.5-7.9 cm and weight of 2.2-7.3 g increases from 3441 ± 942 to 10241 ± 1323 eggs in one clutch. The duration of embryogenesis and survival of shrimp embryos with an increase in water temperature from 18 to 31 ° C is reduced from 42 to 20 days. The optimum is at a temperature of 27 ° C, which ensures the survival of 98% of the embryos. Shrimp M. nipponense can reproduce at a salinity from 0 to 9‰, but the optimum salinity is 5‰ which in the range of optimal temperatures ensures the survival of 98% of embryos with a minimum duration of embryogenesis. Originality. The reproductive characteristics of female M. nipponense from the Dniester population were studied for the first time. It was shown that the fertilized shrimp eggs of the Dniester population differ in size in different areas of the lower reaches. The dependence of the initial (IRF) and final (FRF) realized fertility on the mass of shrimp was found. The duration of embryogenesis and the survival rate of embryos were studied depending on the temperature and water salinity.