Microbiological studies of the round goby (Neogobius melanostomus) from the Puck Bay, southern Baltic Sea.

In summer 2017 numerous dead round gobies ( Neogobius melanostomus) and individuals covered with white coating were observed in the Puck Bay. The aim of our research was to determine the microbiological composition of the round goby from the Puck Bay, focusing on the presence of pathogens. Bacteria were identified by biochemical methods and, by sequencing of 16S rRNA. The dominant bacterial species were Shewanella baltica, Pseudomonas spp. and Aeromonas spp. - opportunistic pathogens, commonly present in many fish species, which may become harmful for the organism in unfavorable conditions. It was the first trial to determine the composition of the bacterial flora of N. melanostomus from that area.

Saduria entomon infected with Hysterothylacium aduncum found in situ in the stomach of cod (Gadus morhua) from the Baltic Sea.

The parasite fauna of cod (Gadus morhus) is well described, but the life cycles of Baltic cod parasites are known only in general terms. Invertebrates commonly found in the stomach of cod are recognized as intermediate hosts in the life cycles of nematodes or acanthocephalans. The aim of this study was to determine the source of infection of Baltic cod with parasites found in situ in invertebrates present in the cod stomach. Our results indicate that Saduria entomon is both a source of infection of Baltic cod with parasites and an intermediate host in the life cycle of Hysterothylacium aduncum in the Baltic Sea.

Great sandeel (Hyperoplus lanceolatus) as a putative transmitter of parasite Contracaecum osculatum (Nematoda: Anisakidae).

In the Baltic Sea, the great sandeel (Hyperoplus lanceolatus), a common fish species that inhabits sandy substrates, is an important element in the diet of marine mammals, sea birds, and piscivorous fish. It can also act as a transmitter of parasites to its predators, but parasitological studies on this species are limited. We sampled great sandeels in April 2016 in two areas of the southern Baltic Sea (SB-south of Bornholm and GG-the Gulf of Gdansk) and found parasitic anisakid nematodes in both locations. The only one species of nematode parasites has been detected: liver worm (Contracaecum osculatum) with average prevalence of infection 8.96%. This is the first study to report on infection of H. lanceolatus with anisakid nematodes in the southern Baltic Sea and our results suggest that the great sandeel may play a role in the transmission of liver worm in the food web of this marine environment.

Host condition and accumulation of metals by acanthocephalan parasite Echinorhynchus gadi in cod Gadus morhua from the southern Baltic Sea.

In this study, we analyzed the relationship between concentration of metals in the host-parasite system (cod - acanthocephalan Echinorhynchus gadi) and Fulton's condition factor (FCF) of the host. The relationship between metal (Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Pb, Sr, Zn) concentrations in E. gadi and cod tissues was expressed as a bioconcentration factor (BCF), the ratio of the concentration in the parasite tissue to that in host tissues. Acanthocephalans accumulated mainly toxic metals (Cd, Pb), as well as Sr, Ca, Na. Cadmium showed the highest bioconcentration in parasites (BCF >200) compared to fish muscle. Significant negative correlation was detected between FCF and the concentration of Cd and Hg in cod liver. In contrast, FCF was positively correlated with the concentration of Hg in acanthocephalan tissues.