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This paper reports the occurrence of three new fish species, extremely rare in the Baltic Sea, and provides new data on their parasite fauna. The fish collected were Barbus barbus (Linnaeus, 1758), Salvelinus fontinalis (Mitchill, 1814), and Scophthalmus rhombus (Linnaeus, 1758). Their taxonomic identity was confirmed through genetic analyses using DNA extracted from fin clips. The stomach contents were examined, and age was determined by otolith or scale readings. Parasitological examinations focused on the skin, vitreous humour, eye lenses, mouth and nasal cavities, gills, gonads, viscera, and muscles. Furthermore, the changes of fish species composition over 20 years in Pomeranian Bay were analysed. The sequence comparisons against GenBank records revealed that sequences obtained for B. barbus and S. rhombus from Pomeranian Bay represent new rhodopsin barcodes. Record of the juvenile B. barbus in this study is the first in the Baltic Sea. Scophthalmus rhombus is a new host for the ciliate Trichodina jadranica, while Neogobius melanostomus (Pallas, 1814) is a new food item in the diet of S. rhombus in the Baltic Sea. Acanthocephalan Pomphorhynchus laevis found in the adult specimen of B. barbus and myxozoan Myxobolus musculi, noted in the juvenile specimen, have not been recorded previously in this fish species in Polish waters. Species collected as bycatch can potentially be used for monitoring potential changes in the overall fish community structure and biodiversity.

Summary: Etmopterus spinax is a deep-sea shark species that inhabits the northeast Atlantic and the western Mediterranean Sea. Skagerrak and Kattegat are reported to be part of the distribution of the species, but it has never been noted in the southern Baltic. Lacking any commercial value and commonly discarded in trawl and longline fisheries, E. spinax has been poorly studied. We reported on the first record of one specimen of E. spinax caught in the Pomeranian Bay on October 13, 2016 at a depth of 10 m. It was a female measuring 42.7 cm in total length. The morphological examination of the specimen was supported with COI barcode analysis, whereas species assignment to the population of origin was conducted based on a control region (CR) sequence of mtDNA. COI and CR sequence searches against GeneBank confirmed its identity as E. spinax and revealed that the specimen shared identical haplotypes with fish from populations in the Azores, Rockall Trough, and west of Ireland in the northeast Atlantic. The stomach contents, parasitic fauna, and hepatosomatic index of the individual were also examined. Only one L3 larval Anisakis simplex nematode specimen was collected from the stomach lumen of the shark. The specimen could have arrived in the Pomeranian Bay along with an inflow from the North Sea. In December 2014, a strong Major Baltic Inflow brought large amounts of water into the Baltic Sea, followed by some inflows of moderate intensity. Keywords: Etmopterus spinax, Anisakis simplex, Pomeranian Bay, Southern Baltic Sea, Inflow from the North Sea

Summary The presence of exotic fish species in the Baltic Sea and its tributaries poses a serious threat for native ichthyofauna, mainly due to the spread of new pathogens. As the accurate identification of species is essential for an effective assessment of changes related to the appearance of non-native species in an aquatic environment, in this paper we tested the usefulness of biometrics and molecular markers in identifying a specimen from the Mugilidae family found in the Odra estuary. The results demonstrated that unambiguous identification of the specimen using biometric features was impossible due to high morphological similarities shared by grey mullets. Unambiguous identification was possible only due to molecular markers, e.g. rhodopsin gene, which helped to identify the collected fish specimen as Liza ramada (Risso, 1827), the first specimen of this species found in the Odra River estuary. The presence of an L. ramada specimen in the Odra River – which could signal the expansion of non-native species into wider ranges – may be linked to climate change or human activity.

Biometric character analyses were conducted on Atlantic sturgeon Acipenser oxyrinchus, a species included in a re-establishment programme in the Baltic Sea basin. The study sought to identify measurable and countable characters most useful for distinguishing A. oxyrinchus from three alien species found in open waters of Poland: Acipenser baerii, Acipenser gueldenstaedtii, and Acipenser stellatus. Measurable characters that contributed most to discrimination included preorbital distance, eye diameter, ventral fin base to anal fin base, and postorbital distance. Among countable characters, the number of lateral scutes made the greatest contribution. The data from the present study may be used to supplement existing systematic keys and lay the foundations for creating a catalogue or atlas of popular species and interspecific hybrids of sturgeon, including their complete systematic determination.

This paper presents the results of studies on endangered and rare non-commercial fish species (Spinachia spinachia, Nerophis ophidion, Syngnathus typhle, Agonus cataphractus, Pholis gunnellus, Enchelyopus cimbrius, Cyclopterus lumpus) and one lamprey species (Lampetra fluviatilis), recorded as bycatch during monitoring surveys in 2010–2013 in the Pomeranian Bay. Two species were observed for the first time in the Pomeranian Bay: A. cataphractus and E. cimbrius. Descriptions of parasite fauna are provided for C. lumpus and E. cimbrius, which were infected with four pathogenic species from Neomonada, Digenea, Nematoda, and Acanthocephala. Almost all parasite species were new in the hosts examined.

The first occurrence of striped red mullet Mullus surmuletus in the Pomeranian Bay (in 2007) and the occurrence of three very rarely noted species (tub gurnard Chelidonichthys lucerna , Atlantic horse mackerel Trachurus trachurus , thicklip grey mullet Chelon labrosus ) collected in 2007–2008 in the Pomeranian Bay, Szczecin Lagoon and Lake Dąbie are reported. Their expansion is probably due to increased sea temperatures resulting from climate change, as well as the inflow of saline water. The ‘visitors’ hosted eight pathogens from four taxonomic groups: Protozoa, Nematoda, Acanthocephala and Mollusca. Nematodes, the most numerous ones, were found in three host species. All the parasite species were new for the hosts examined; only the larvae of the acanthocephalan Corynosoma strumosum had already been recorded in one of the hosts ( Chelidonichthys lucerna ). The stomachs of almost all the fish examined were empty, but the species composition of the parasite fauna found showed that the fish must have ingested some food in the Pomeranian Bay.

Background. Monitoring the genetic diversity of fish populations can provide information necessary to determine fishing quotas for the commercially caught species. One of the species subjected to intensive exploitation is the yellowstripe scad, Selaroides leptolepis (Cuvier, 1833), commonly occurring in the coastal waters of Vietnam, Cambodia, Malaysia, and Indonesia. This paper is the third part of a larger project: ”Development of a genetic-based system for identification of food products from fisheries and aquaculture introduced to the European Union customs area”. Materials and methods. Fin fragments of the yellowstripe scad, Selaroides leptolepis, were obtained in 2012 and 2013 from local markets in Vietnam (SVN), Cambodia (SKH), Malaysia (MMY), and Indonesia (MID). The analyses focused on the amplification and sequencing of a fragment of the nuclear rhodopsin gene which utilized as identification label. Subsequently, in the obtained SVN, SKH, MMY, and MID samples, 11 microsatellite regions (SRR) were analysed. Sequence analyses were performed using the BioEdit and BLAST software, while the analysis of the obtained SRR data was conducted using the GenAlEx software. Results. The analysis of the obtained loci variants divided the investigated populations into two genetically homogeneous groups: the Vietnamese–Indonesian group and the Malaysian–Cambodian group. The analysis of genetic diversity revealed statistically significant deviations from the Hardy–Weinberg equilibrium in the investigated populations and indicated the Vietnamese population as the most stable, while the Malaysian population as the least stable. Conclusion. The study provides information on the genetic diversity of the investigated populations and allows assignment of the captured fish to the geographical regions specified. Moreover, indicate that among analysed populations the safest populations were those caught in the local fisheries (continental shelf) of Vietnam and Cambodia due to their high mean genetic diversity.

Exotic species of acipenserid fishes have been frequently encountered in the commercial catches of the Baltic Sea, since the early 1990s. Such sightings are rarely reflected as published records. The present paper provides detailed descriptions of two specimens of Russian sturgeons, Acipenser gueldenstaedtii caught in the Exclusive Polish Economic Zone of the Baltic Sea.

Background. Genetic traceability of seafood as well as population identification using molecular methods provide useful information about the fish origin and are important for protection of overfished populations, as well as for monitoring illegal, unreported, and unregulated (IUU) fisheries. The presently reported study focused on Indian mackerel, Rastrelliger kanagurta (Cuvier, 1816)—a pelagic species with a wide range of distribution—especially important for many tropical countries, such as India, Philippines, and Thailand. This paper is the first part of a larger project: ”Development of a genetic-based system for identification of food products from fisheries and aquaculture introduced to the European Union customs area”. Materials and methods. Samples consisting of fin fragments of Indian mackerel were obtained from local markets in Thailand (MTH), Vietnam (SVN), Cambodia (SKH), and Madagascar (SMG) within 2012–2013. Two genes were analysed: nuclear rhodopsin gene (RH1) and mitochondrial D-loop (D-loop) region through RFLP analysis simulation and sequencing. Additionally, the samples from Cambodia and Madagascar were analysed with eight microsatellite loci (SSR). The data processing was aided by GenAlEx 6.5 and GeneClass2 software. Results. A comparison of the RH1 gene section revealed a total homology among the studied samples. A comparative analysis of D-loop sequences in the studied groups revealed intrapopulational diversity for MTH-, SKH-, SMG-, and SVN samples, at the level of 1, 1, 0.5, and 0.6 percentage points, respectively. Furthermore, the D-loop sequences identified a characteristic restriction site for SMG population. Based on the allele frequencies, we randomly assigned selected individuals to their original populations. GeneClass2 software correctly assigned only 16 out of 21 individuals to either the Cambodian or the Madagascar population, which jointly constituted 76% of all samples. We demonstrated, using AMOVA and GenAlEx 6.5, that the highest level of variability occurred among individuals within the respective populations, while the lowest interpopulation diversity was between the SMG and SKH populations. Conclusion. Our results may help the relevant authorities in the countries of the European Union to identify Indian mackerel and especially its products and trace them to the respective locality. Our findings may also be used for species-specific conservation measures hopefully undertaken by fisheries authorities of the countries where we took our samples. Results on other fish species, prepared in the frames of the same project, will be presented in other papers that will follow soon.

Background. Asian pangasiids (Actinopterygii: Siluriformes: Pangasiidae), commonly referred to as “panga”, have recently became an important item on the European fish markets. The fish are currently imported from south-east Asia but the growing consumers’ demand is likely to motivate European fish growers to culture the “panga” locally. This in turn could bring about unforeseeable consequences for the aquatic environment. The presently reported study provides the first record of a pangasiid fish (two specimens) from the European natural waters. We attempted to identify the fish through complex morphometric procedures and to study all their parasites, thus determining their potential threat for the environment. Materials and methods. Two specimens of pangasiid fish were captured in a pond, in the city of Szczecin, Poland. The fish were examined following procedures commonly accepted in morphological studies yielding detailed measurements. The key structures were described and illustrated (e.g., the shape of dentition on both the vomerine and palatine plates). The measurements were taken with an electronic calliper and a dissecting microscope (Nikon SMZ 1000), coupled with the Lucia Measurement System. Additionally, during necropsy, selected organs were checked for the presence of parasites. Results. One of the fish specimens hosted the monogenoid parasite, Thaparocleidus caecus, that has never been found in Europe. Metric and meristic characters of fish studied, as well as the presence of monogenoid T. caecus suggest that the fish found were representatives of Pangasianodon hypophthalmus, however, some features, especially those related to the ratio between fins and body or total length, differ markedly from the species description. Comparative analysis suggested that the two specimens collected in Szczecin are hybrids, most likely of P. hypophthalmus with other species, of unknown origin, presumably imported from Thailand. Conclusion. The specific identity of pangasiids imported alive to Europe should be monitored in the future. Additional genetic studies are needed. The monogenoid parasite found on the fish studied poses no threat to the native ichthyofauna (because of its very narrow host-specificity).

Background. The presently reported finding of leopard pleco, Pterygoplichthys gibbiceps (Kner, 1854) (Loricariidae), in open waters of the Brda River in the centre of Bydgoszcz, constitutes the first record of a south-American loricariid fish species in Poland. The specimen found is described and illustrated. The finding is discussed in association with other alien species sightings in Poland. The described leopard pleco is possibly the next example of an emerging alien fish species in inland Polish waters.

Global consumption steadily increases due to development of aquaculture but also more efficient fisheries sector. Therefore, fish processing plants and ultimately consumers face products from new fish species which significantly differ in case of their nutritional values, technological or culinary properties. The aim of the study was to randomly collect specimens of bigeye sea perch, Helicolenus barathri; New Zealand sole, Peltorhamphus novaezeelandiae; white bass, Morone chrysops; thicklip grey mullet, Chelon labrosus and ridge scaled rattail, Macrourus carinatus and provide multidimensional characteristics i.e. species authentication, proximate assessment, structure and texture analysis as well sensory evaluation. Study confirmed authenticity of all fish samples and new DNA barcodes were introduced into database of fish profiles. Chemical composition of fillets differed significantly among species, and the unfavourable nutritional values had ridge scaled rattail, bigeye sea perch and New Zealand sole which had unfavorable fatty acid profile, high atherogenic (AI) and thrombogenic (TI) indexes, and low hypocholesterolemic to hypercholesterolemic acids ratio. On the other hand, fillets of freshwater white bass had the best PUFA:SFA ratio, and favourable TI and AI indexes from the consumer’s health point of view. Moreover, fillet of the white bass was selected by panellists as the most desirable. Structural analysis also revealed different degree of undesirable changes in fillets observed as breakdown of myofibrils and connective tissue. Multidimensional analysis characterized randomly selected sample and provided a set of useful information both for customers and fish processing sector.