The peculiarities of nearshore fish communities in the Vita River mouth and Dnipro River straits

Purpose. To investigate the current state of nearshore fish communities and peculiarities of aquatic plants and zoobenthos distribution in the Vita River mouth and Dnipro River channels. Methodology. The study was carried out in summer and autumn 2022 at 4 sampling sites in the Vita River mouth and at 3 sampling sites in Dnipro River straits in the Zhukov Island area. Fishes were caught by a beach seine (6 m in length, 1.5 m in height, 1.5 сm mesh size). Two to three hauls were made at every site depending on the riverbank and bottom structure. Fishes were identified to the species level keeping them in containers with fresh water. Then they were released alive to the river. Findings. Higher aquatic vegetation of the investigated area of the Dnipro River straits was presented mainly by high grasses and attached vegetation with free-floating leaves (associations of common reed Phragmites australis – crisp-leaved pondweed Potamogeton crispus; common reed Phragmites australis + lesser bulrush Typha angustifolia – Potamogeton crispus; yellow water-lily Nuphar lutea). These sites were characterized by optimal oxygen regime for the development of periphyton and lithophilic groups of zoobenthos, the main prey for benthophagous and euryphagous fishes. The biomass of benthic invertebrates was 9.44 g/m2, and their abundance was 24400 ind./m2. In the Dnipro straits, 25 fish species of 5 genera were recorded. Two thirds of them were native species; the most abundant were white bream (Blicca bjoerkna Linnaeus, 1758), roach (Rutilus rutilus Linnaeus, 1758), and monkey goby (Neogobius fluviatilis Pallas, 1814). The share of neolimnetics was 28%, among which gobies (Gobiidae) dominated. In general, long-cycle fishes dominated (44%). Of total species number, 52% were limnophiles, and 32% were reophiles. The share of the psamolithophiles was 40%, and phytophiles were 40%. It shows that these river reaches are very important for spawning the mentioned ecological groups of fish. In the Vita River mouth area, the free-floating vegetation dominated, which was represented by associations of salvinia or floating fern (Salvinia natans) and common or small duckweed (Lemna minor). The dominant phytophilous group of zoobenthos had a biomass of 5.78 g/m2 and abundance of 8365 ind./m2. In the this area, 14 fish species of 7 genera were registered, the most abundant of which were white bream (Blicca bjoerkna Linnaeus, 1758), rudd (Scardinius erythrophthalmus Linnaeus, 1758), and roach (Rutilus rutilus Linnaeus, 1758). The native species formed the maximal share of the fish fauna. Of total species number, 14.3% were neolimnetics and 14.3% remote invaders. Fish community of coastal areas of the Vita River was presented by long and medium cycle species. The share of indifferent and limnophiles fish species were 50 and 43% respectively. Phytophiles dominated in relation to the spawning substrate (57%). Five fish species are included into the protection lists of various levels: knife (Pelecus cultratus Linnaeus, 1758), European bitterling (Rhodeus amarus Bloch, 1782), ide (Idus idus Linnaeus, 1758), common nase (Chondrostoma nasus Linnaeus, 1758), asp (Aspius aspius Linnaeus, 1758). Originality. A comprehensive analysis of vegetation associations, zoobenthos and fish communities of the Vita River mouth area and Dnipro River straits was carried out. Ecological structure of the littoral fish communities was established by species composition and relative abundance, the feeding type, life cycle, spawning type and relation to the water current. Practical value. The preservation of the landscape and biotope conditions of the Vita River mouth area and adjacent Dnipro straits is important for the reproduction of typical ichthyological communities of the Dnipro River middle section.