Analyses of intestinal content of round goby Neogobius melanostomus (Pallas, 1814) in the Serbian part of the Danube River Basin

Abstract

In the Serbian part of the Danube River, of the 25 fish species recorded, five species from the Gobiidae family have a participation with 10-20%. Since the early seventies, the spreading of the gobiids along the Danube River has been reported, mainly owing to the construction of dams and channels linking larger rivers. The round goby Neogobius melanostomus is a fairly small bottom-dwelling fish, living in brackish and freshwater environments. It is typically found near sandy, stony bottoms. This fish mostly stays in one place with noticeably restricted movement. A patchy distribution and long distances between native regions of occurrence and newly settled areas is characteristic for the current world distribution of the species. Most probably, transport has occurred in ballast waters. The aim of our study was to analyse the intestinal content of round goby in the Serbian part of the Danube River Basin. The fish samples were collected during October 2018 at three localities in the Danube River (Zemun and Stari Slankamen) and Velika Morava River (Ljubičevo). A total of 35 individuals of round goby were collected and examined. Fish were caught with electrofishing ((HONDA 1,2кW, 6 А) and transported to the laboratory, where the analysis of their intestines for food items was conducted. The intestines were examined under an Olympus binocular microscope and an Olympus stereomicroscope. Identification was carried out to the species level, using the appropriate identification keys. At the locality Ljubičevo, eight from 18 sampled specimens were without intestine content. At the localities Zemun and Stari Slankamen, one specimen of ten and seven, respectively, was without food items. The analysis showed that the intestinal content of the round gobies consisted of representatives of the family Gammaridae (Dikerogammarus sp.), insect larvae (Trichoptera), Gastropoda, Bivalvia (family Unionidae) and Oligochaeta. The diet of fish samples from Ljubičevo consisted mostly of gammarids and oligochaets, while this of fish from Zemun and Stari Slankamen from caddisfly larvae and molluscs. Round gobies are voracious feeders, eating mussels and other molluscs, with up to 60% of their diet made up of mussels in some places. They also eat aquatic insect larvae and the young and eggs of other fish.