Wintering of the eastern subtropical freshwater shrimp (Macrobrachium nipponense de Haan, 1849) in the conditions of the Dnister River basin

Purpose. To study the characteristics of wintering of Macrobrachium nipponense in natural conditions of the Lower Dniester basin and experimental assessment of the effect of physical condition, soil composition and type of shelter on the survival of wintering shrimps. Methodology. The results of field and experimental studies conducted in 2018–2020 were used in the study. The locations and conditions of mass wintering of shrimps in natural conditions in the lower reaches of the Dniester River were studied. The abundance of wintering individuals was determined by the method of direct counting and their physical condition was analyzed. Shrimps were kept in a RAS at the Laboratory of Aquatic Bioresources and Aquaculture of Odesa State Ecological University, where environmental parameters were maintained as close as possible to the conditions of wintering under natural conditions. In chronic experiments, the selectivity and effect of the composition of natural substrates and the thickness of the soil bed on shrimp survival were investigated. The selection and effectiveness of the shrimp's use of above-ground shelters of various natural and anthropogenic origin for shrimp wintering was assessed depending on their physical condition (presence or absence of injuries). Shrimp for experiments were caught in October - November in the lower reaches of the Dniester River and the Dniester estuary. The location of mass wintering of shrimps was recorded using a GPS navigator. Findings. It was established that shrimp M. nipponense in natural conditions of the Lower Dniester river winters in aboveground shelters (of natural and anthropogenic origin) or by burrowing into the soil. The shrimp's choice of aboveground shelters for wintering in natural conditions depended on their physical condition. Injured individuals (lost claws and limbs) preferred easily accessible aboveground shelters (sheaves of grass, flooded snags). Healthy individuals wintered in cracks between plant roots and stones. A significant part of shrimps overwintered in aboveground shelters of anthropogenic origin. The most complex and reliable aboveground shelters of natural origin were occupied by the least damaged shrimp individuals. More than 59% of shrimps are buried in the soil (soil shelters) for wintering. Healthy individuals prefer sandy soils or soils that contain sand. The highest yield of healthy shrimp overwintering was observed on sandy or sandy-gravel soils with a thicker soil layer. The depth of burial of shrimp depended on soil composition. It was the maximum in soils consisting of sand, sand-gravel mixture and chernozem or chernozem with inclusions of gravel. The survival of wintering individuals was inversely dependent on the depth of burial. The maximum yield of uninjured individuals from wintering was observed when they were buried in the soil, the minimum — when using aboveground shelters. The share of surviving injured shrimp in soil shelters decreased in proportion to the severity of the injury. Maximum survival of injured individuals was ensured by wintering in aboveground shelters. Originality. For the first time, the data of field observations on wintering of alien shrimp M. nipponense in the conditions of the Lower Dniester basin are presented. Locations and conditions of mass wintering in natural conditions have been established. As a result of experimental studies, an analysis of the selectivity and effectiveness of the use of soil and aboveground shelters of various natural and anthropogenic origins by shrimp during wintering, their selectivity depending on the physical condition of wintering individuals (presence or absence of injuries) is given.