| Abstract [eng] |
The monkey goby (Neogobius fluviatilis Pallas, 1814) is an invasive fish from the Ponto-Caspian region that has rapidly spread in European waters only in recent decades. In Lithuania, N. fluviatilis was first discovered in 2015, in the river Neris, on the border with Belarus, where it entered through an artificial canal system, connecting the Neris and Berezina rivers (the right tributary of the Dnieper). Although almost a decade has passed since N. fluviatilis entered the Nemunas basin, there is still very little knowledge about the impact of this invasive species on fish communities, and no detailed studies have been conducted on the nutritional characteristics of N. fluviatilis and the competition of N. fluviatilis with local fish species in the Nemunas basin. In this work, the fish communities in the Kaunas water reservoir, rivers Neris and Nemunas were evaluated, the diet of N. fluviatilis was determined in different habitats in the Nemunas basin. The diet of N. fluviatilis and the local fish – gudgeon (Gobio gobio) – were compared, since they occupy similar habitats. In 2021-2022, fish were caught in five research locations in the Nemunas basin with an electrofishing device and a juvenile trawl, their abundance and biomass were determined. Fish nutrition was determined by stomach content analysis method. A total of 272 N. fluviatilis and 60 G. gobio stomachs were analyzed. The estimated relative abundance of N. fluviatilis showed that the older the invasion, the relatively more individuals are present in that fish community. Analysis of the stomach contents showed that the diet of N. fluviatilis is dominated by the larvae of Chironomidae in stagnant water, in rivers N. fluviatilis also feed on Chironomidae larvae, but a large part of the diet consists of bivalve molluscs (Sphaeriidae), mayflies (Ephemeridae, Baetidae) and caddisflies (Hydropsychidae). Relative importance index (IRI) was used to determine the importance of food items, Schoener's index was used to determine nutritional overlap. It was found that the nutritional niches of N. fluviatilis and G. gobio overlap by 52.4%. Data were processed using Microsoft Excel 2021 and PAST 4.11 programs (Mann-Whitney U and Kruskal Wallis tests were used). |
