The spread of aquatic non-indigenous species (NIS) is recognised as a major threat to the recipient regions ecosystems. The present study reviewed all NIS that have been introduced to the marine waters of the European Union (EU) until 2021, and their introduction pathways. Further, the study statistically analysed temporal trends in new NIS introductions and addressed uncertainties in relation to transporting pathways. Time-series analyses indicated that the observed trends in new NIS introductions have followed smoothly increasing trajectories for the entire study area, Mediterranean Sea, North-East Atlantic Ocean, and the Baltic Sea, whereas abrupt increase was detected for the Black Sea. It is noteworthy that the increasing trends started to slow down at the end of 2010s. Strongly increased research interest towards marine invasions since the early 2000s, and new environmental policies likely affected the observed trends. Future updates will be key to assessing whether this slowdown is truly a persisting trend or only an anomaly in the long term. The pathway assessment suffered from notable uncertainties, as the assigned confidence levels for pathways were low or unassigned for a large proportion of the introduced NIS in all study regions. Transport by shipping vectors was assigned as the most common pathway (51%) for new NIS introductions to EU seas, although there was very rarely direct evidence of this. The study highlights the need to overcome the pathway uncertainties, as robust information on introduction pathways is critical to manage new NIS introductions effectively.

In terms of ichthyology, Bosnia and Herzegovina (BiH) is one of the most interesting parts of Southeast Europe, due to its rich biodiversity and high level of endemism. Despite its relevance, the entire territory has been poorly explored. Here, we provide an updated inventory of the current state of knowledge on fishes, including lampreys, from the freshwaters of BiH by hydrographic basin, with recent distributional data and updated taxonomic status reviewed and compared with previous lists. The checklist was compiled based on the existing scientific and grey literature, technical reports, scientific congresses, academic dissertations, and unpublished/personal observations. In total, 123 species including diadromous and euryhaline fishes have been documented in BiH freshwaters to date. Of these, 110 are primarily freshwater. In comparison to the last published monography (Sofradžija 2009), we present a 9% increase in species number (11 species), resulting mainly from taxonomic re-evaluations of existing taxa on the basis of new information and the adoption of a new changes in the taxonomic status of several species. Among the valid primarily freshwater species, 87 are native and 23 are non-native. A total of 38 endemic species have restricted distribution, and are threatened by numerous anthropogenic pressures. Four species are considered endemic only to BiH: Cobitis herzegoviniensis Buj & Šanda, 2014; Phoxinellus pseudalepidotus Bogutskaya & Zupančič, 2003; Telestes dabar Bogutskaya, Zupančič, Bogut & Naseka, 2012; and T. metohiensis (Steindachner, 1901). In total, 75 genera and 34 families are represented: Leuciscidae is represented by 37 species, the Salmonidae by 13, followed by the Cyprinidae, Cobitidae and Percidae, each with eight species. The native species richness follows a pattern similar to that observed in other southern European countries. A national list of endangered species has not yet been proposed to BiH and management strategies for their protection or conservation are also not implemented. Hopefully, this updated checklist will serve as a basis for future research aimed at understanding the origin and status of conservation of the BiH fishes diversity, and supporting effective management and conservation programmes.

Marine litter is an issue of growing concern in the Mediterranean, one of the most polluted regions in the world. In the marine environment, floating marine litter (FML) can pose a threat, but also represent a short-term habitat for various marine organisms, including fish that can temporarily reside in these unique surroundings. However, unlike the FADs, the role of FML as habitat, shelter or dispersal vector for fish remains poorly documented, and insufficiently is known about the ecological functions of these artificial habitats or associated behavioural responses of fish. This study presents the diversity and abundance of fishes associated with FML. Data were collected accidently during other research and through contributions from non-scientific observers in fisheries and maritime traffic over the last two decades in the Croatian part of the eastern Adriatic Sea. A total of twelve fish species from eight families were identified, Balistidae being the most frequent (46.34%), followed by Carangidae (34.14%) and Serranidae (31.70%); Balistes capriscus was the most frequent species (43.34%), followed by Polyprion americanus (31.70%). Juveniles predominated with the >95% suggesting that FML may act as important shelter and nursery areas, contributing to the recruitment and redistribution of juvenile fish. Due to the limited availability of natural floating substrates in pelagic zones, fish appear to opportunistically exploit available habitats for shelter and foraging, showing similarity with FADs. This study highlights the value of Local Ecological Knowledge provided by civil society, which proved to be an important source of information on fish associated with FML.

The Mediterranean flyingfish Cheilopogon heterurus (Rafinesque, 1810) is known to have a broad global distribution, with reports from the Pacific Ocean, including Australian waters (Gomon et al., 1994), and the western Atlantic, such as the Gulf of Mexico (Smith, 1997). However, in the northeastern Atlantic, the species is only sporadically captured in areas like Denmark, southern Norway, southern England, and France (Parin, 1986). South of the Strait of Gibraltar, C. heterurus has been documented off the coasts of Morocco (Lloris and Rucabado, 1998), Mauritania (Maigret and Ly, 1986), and likely from Senegal to the Gulf of Guinea (Blache et al., 1970). Of the nine exocetid species identified in the Mediterranean Sea (Parin, 1986, 1996; Parin and Belyanina, 2000; Ben Souissi et al., 2005; Capap & eacute; et al., 2016), only five are considered part of the Adriatic ichthyofauna (Lipej and Dul & ccaron;i & cacute;, 2010; Dul & ccaron;i & cacute; and Kova & ccaron;i & cacute;, 2020). C. heterurus is an extremely rare species in the Adriatic Sea, typically caught by accident (Dul & ccaron;i & cacute; and Kova & ccaron;i & cacute;, 2020). Although listed as part of the Adriatic ichthyofauna, scientific literature lacks substantial documentation of its presence. There is only a single record of an individual in the Natural History Museum in Rijeka and a singular catch from the middle Adriatic with no further details (Kova & ccaron;i & cacute; et al., 2020). The purpose of this paper is to present the northernmost record of C. heterurus in the Mediterranean Sea and the first confirmed documentation of the species in the Adriatic Sea.

This study reports the first capture of Lagocephalus sceleratus in the northern Adriatic, specifically in Medulin Bay at a depth of 19.7 m. The specimen, a 522 mm male weighing 1330 g, was caught on 13 May 2024. This is the fourth record in the Adriatic and the northernmost one for both the Adriatic and Mediterranean seas. Stomach analysis revealed bivalves, gastropods, sea urchin fragments, and inorganic particles. The further spread of this tetraodontid species in the Adriatic poses ecological and socio-economic risks, such as disruptions to fisheries, biodiversity loss, and threats to marine ecosystems. Effective management requires monitoring, regulation, public education, and citizen science involvement.

Records of Monrovia doctorfish Acanthurus monroviae in the Croatian part of the Adriatic Sea are reported. The first occurrence of this non-native species was detected by one of the authors and was subsequently publicly reported by citizens via social media. The origin of introduction is unknown, but it is most likely active migration from the Mediterranean through the Strait of Otranto.

New records of introduced species in the Mediterranean Sea (December 2025)

Brama brama, the Atlantic pomfret or ray's bream, is uncommon in the Mediterranean Sea and very rare in the Adriatic area. We report two historical records of this species from the northern Adriatic Sea, which represent the northernmost records in the Mediterranean. The detailed morphological data of these specimens and their comparison with available data from specimens from the Mediterranean Sea reveal the variability of the morphology of adult specimens

The age and growth of the blackspot seabream, Pagellus bogaraveo, were determined by examining sagittal otoliths from fish sampled in the eastern Adriatic Sea. A total of 674 specimens (181 males, 90 hermaphrodites, 108 females, and 295 immatures) ranging from 8.80 to 47.27 cm (21.93 ± 9.00 cm) in total length were analyzed. The maximum observed age for the whole sample was 13 years. The sample was dominated by 1-year-old specimens as a consequence of an abundance of juvenile specimens collected by beach seines. Growth was described by the von Bertalanffy growth curve (L∞ = 52.3 cm, K = 0.15 year−1, t0 = 0.49 year, R2 = 0.97), and the growth performance index (Φ’) was 2.61. The length, width, thickness, and mass of the otoliths were compared with the total length and age of P. bogaraveo from the eastern Adriatic. The analysis showed that the measures were adequate predictors of age. These results can be of value for more effective management measures aimed at the conservation of this species.

This Collective Article presents new information about the occurrence of 23 marine taxa that belong to five Phyla: two Chlorophyta, one Annelida, six Mollusca, three Arthropoda, eleven Chordata (one Ascidiacea, one Elasmobranchii and nine Teleostei) and extending from the Western Mediterranean to the Levantine Sea. All these records were reported from nine countries from the western to the eastern Mediterranean Sea, with a broad biogeographical coverage as follows: Spain: first records of the sacoglossans Cyerce graeca and Placida tardyi for the Alboran Sea and first records of the nudibranch Marionia gemmii for the Mediterranean waters of Spain; first records of nudibranch Algarvia alba in the Mediterranean Sea. Italy: First report of the long-legged crab Paragalene longicrura, a further new Mediterranean record of the rare offshore rockfish Pontinus kuhlii, first documented record of the spiny butterfly ray Gymnura altavela in Sardinia (Tyrrhenian Sea), new record of the red‐spotted wrasse Lappanella fasciata from the Messina Strait, first documented record of the rarely observed brown moray Gymnothorax unicolor in the Ionian coast, first record of the colonial ascidian Botrylloides israeliensis, first record of the Morocco dentex Dentex maroccanus, first record of mottled shore crab Pachygrapsus maurus and of an adult specimen of barracudina Lestidiops sphyrenoides in the Adriatic Sea, and further new Mediterranean records of Ross worm Sabellaria spinulosa along the same coast. Tunisia: second record of smalleye squaretail Tetragonurus cuvieri from the African Mediterranean coast. Slovenia: first records of the sea slug Trapania graeffei and Melanochlamys wildpretii, with the last one also representing the northernmost finding of this species. Croatia: northernmost record of the endangered twaite shad Alosa fallax in the Adriatic coast. Albania: first records of the Mediterranean spearfish Tetrapturus belone. Türkiye: first record from the Aegean coasts for Türkiye of the green macroalgae Cladophora battersii and Valonia aegagropila. Israel: first record of the skeleton shrimp Caprella acanthifera in the Southeastern Mediterranean Sea. Syria: first record of the Smooth grenadier Nezumia aequalis from Syrian marine waters.

The first record of the little known stomatopod Parasquilla ferussaci (Roux, 1828) in the Adriatic Sea is documented. One specimen was captured near islet Blitvenica in the eastern Adriatic (Croatian coast) on 26 January 2021 with a bottom trawl. This record indicates the extension of the known distributional range of this species in the Mediterranean Sea. Here we also provide the first data on the molecular identification of Parasquilla ferussaci supported by the detailed morphological description of the investigated specimen. Parasquilla is derived as a sister group to Faughnia , which together are sister to the genus Pseudosquillopsis .

Over the past four decades, the understanding of Mediterranean oceanography has evolved considerably. From a purely stationary view, there has been a shift to a concept that considers the Mediterranean as a highly dynamic sea in which ocean-typical processes occur on smaller spatial and temporal scales. The recent discovery of the mechanism called BiOS (Adriatic-Ionian Bimodal Oscillating System) has further highlighted the highly variable nature of Mediterranean oceanography and the interconnectedness of its sub-basins. The BiOS is a mechanism by which the deep thermohaline cell of the eastern Mediterranean, originating in the southern Adriatic, is connected to the upper circulation of the Northern Ionian Gyre via positive feedback, causing a decadal circulation change that leads to a redistribution of salt throughout the Mediterranean. The effects of this variability are manifold: decadal modulations of the intensity of winter convection in the southern Adriatic, with variations in the volume and thermohaline properties of the dense water produced; variations in preconditioning in the eastern Mediterranean, affecting the salinity of the intermediate Levantine waters; influence on biodiversity in the Adriatic due to the import of Lessepsian organisms or those of western Mediterranean and Atlantic origin; variations of the trophic regime in the Ionian Sea due to the different vertical dynamics of the nutricline during the cyclonic or anticyclonic circulation of the Northern Ionian Gyre; significant contribution to the preconditioning of the northwestern Mediterranean Sea by the salinity variability of the Levantine Intermediate Water. In this study, the BiOS mechanism, the underlying theory, and the implications for the oceanographic features of the Mediterranean Sea are presented, based on the extensive literature published in the last three decades and some new analyses.

To enrich spatio-temporal information on the distribution of alien, cryptogenic, and neonative species in the Mediterranean and the Black Sea, a collective effort by 173 marine scientists was made to provide unpublished records and make them open access to the scientific community. Through this effort, we collected and harmonized a dataset of 12,649 records. It includes 247 taxa, of which 217 are Animalia, 25 Plantae and 5 Chromista, from 23 countries surrounding the Mediterranean and the Black Sea. Chordata was the most abundant taxonomic group, followed by Arthropoda, Mollusca, and Annelida. In terms of species records, Siganus luridus, Siganus rivulatus, Saurida lessepsianus, Pterois miles, Upeneus moluccensis, Charybdis (Archias) longicollis, and Caulerpa cylindracea were the most numerous. The temporal distribution of the records ranges from 1973 to 2022, with 44% of the records in 2020-2021. Lethrinus borbonicus is reported for the first time in the Mediterranean Sea, while Pomatoschistus quagga, Caulerpa cylindracea, Grateloupia turuturu, and Misophria pallida are first records for the Black Sea; Kapraunia schneideri is recorded for the second time in the Mediterranean and for the first time in Israel; Prionospio depauperata and Pseudonereis anomala are reported for the first time from the Sea of Marmara. Many first country records are also included, namely: Amathia verticillata (Montenegro), Ampithoe valida (Italy), Antithamnion amphigeneum (Greece), Clavelina oblonga (Tunisia and Slovenia), Dendostrea cf. folium (Syria), Epinephelus fasciatus (Tunisia), Ganonema farinosum (Montenegro), Macrorhynchia philippina (Tunisia), Marenzelleria neglecta (Romania), Paratapes textilis (Tunisia), and Botrylloides diegensis (Tunisia).

A biometric analysis was performed on a sample of 420 specimens of the blackspot seabream, Pagellus bogaraveo (Brunnich, 1769), from the eastern Adriatic Sea. The total length of all specimens ranged from 9.2 to 47.8 cm (23.70 ± 7.63 cm). Eighteen morphometric and eight meristic characteristics were determined. There were no statistically significant differences between the sexes in the morphometric and meristic characteristics of the blackspot seabream in the Adriatic Sea. Regarding meristic characteristics, there are no significant morphological differences between the blackspot seabream population in the Adriatic Sea and that in other areas of the Mediterranean Sea and the eastern Atlantic Ocean. Relative growth was studied by comparing changes in morphological characteristics with growth in total length and head length. The results indicate the presence of a single population of P. bogaraveo in the Adriatic Sea.

This work presents refined, updated subregional and regional non-indigenous species (NIS) inventories for the Mediterranean Sea, validated by national and taxonomic experts, with species records observed until December 2020. These datasets will be used as the baselines for the implementation of the Integrated Monitoring and Assessment Programme for the Mediterranean (IMAP) and the Mediterranean Quality Status Report 2023. In total, 1006 non-indigenous species have been found in Mediterranean marine and brackish waters. The highest numbers of NIS were observed in Israel, Türkiye, Lebanon and Italy. Approximately 45 species were categorized as data deficient, either due to lack of consensus on their alien status or the validity of their identification. Polychaeta, Foraminifera and macroalgae were the groups with the highest numbers of controversial species. There was a general increase in the yearly rate of new NIS introductions after the late 1990s, which appears to be slowing down in the last decade, but this may be confounded by reporting lags and differential research efforts. Between 1970 and 2020 there has been a steep increase in the proportion of shared species present throughout all four Mediterranean subregions, which are predominantly transported via shipping and recreational boating. While Lessepsian species are gradually spreading westwards and northwards, there is still a considerable invasion debt accumulating in the eastern and central Mediterranean.

By introduction of DNA barcodes in Adriatic larval fish identification possible presence ofnew Gobiidae - Buenia massutii Kovačić, Ordines, and Schliewen, 2017, was noticed. Till now, occurrence of this species was restricted only to the Western Mediterranean and to the neighbouring part of the Atlantic Ocean.

The paper presents an analysis of biogeographic and habitat distribution patterns, and the conservation status data of Adriatic fishes, based on the last published checklist and evidence-based critical analyses of species presence. The total number of species recorded in the Adriatic is 449. The Adriatic has 58.8% of Mediterranean species richness, 76.1% of its families, and 87.8% of its orders. Among species discovered in the Adriatic after 2010, twelve species were attributed to biological invasion, mostly Atlantic immigrants or alien species, and ten species were attributed to improved research on the native ichthyofauna of the Adriatic area. About 58% of species are native species of Atlanto-Mediterranean origin, 21% are native species of wider global occurrence, 15% are Mediterranean or Mediterranean and Black Sea endemics and 5% originated outside Mediterranean Sea. The majority of species inhabit the benthic environment (71.9%), while others occur in the pelagic environment (20.7%) or are euryhaline (7.3%). The benthic littoral species are the most numerous Adriatic fishes, representing 40% of all species richness, whereas pelagic fishes are mainly eurybathic or epipelagic; only 3.6% of species are deep pelagic species. A Red Book of marine fishes of the Adriatic Sea is urgently needed to assess their conservation status, covering the entire Adriatic Sea and reviewing all fish species to assess their conservation status.

In this Collective Article on alien and cryptogenic diversity in the Mediterranean Sea we report a total of 19 species belonging to nine Phyla and coming from nine countries. Several of these records concern fish species, and of particular interest are the first records of: Terapon puta for Italian waters; Pteragopus trispilus from Malta; Plotosus lineatus from Cyprus; and the northernmost Mediterranean record of Lagocephalus sceleratus. The northernmost Mediterranean record was also reported for the sea urchin Diadema setosum. The portunid crab Thalamita poissonii was recorded for the first time in Libya. The copepod Pseudodiaptomus marinus was recorded for the first time in the Marmara Sea. The polychaete Branchiomma luctuosum was recorded for the first time from the Mediterranean coast of France. The alien anemone Diadumene lineata was recorded for the first time from Slovenia. The macroalgae Sargassum furcatum was recorded for the first time from Italy. The new Mediterranean records here reported help tracing abundance and distribution of alien and cryptic species in the Mediterranean Sea.

The paper reports the first record of Nemichthys scolopaceus leptocephalus in the Adriatic Sea, including a detailed description of the specimen with morphometric measurements and meristic counts. A single leptocephalus specimen was caught on 18th September 2016 in south Adriatic with a small mid-water trawl at a depth of approx. 120 meters. Further research is needed to reveal more information about the distribution and potential spawning and nursery areas of slender snipe eel as well as the mechanism of retention and dispersion of their larvae in the Adriatic.

By introduction of DNA barcodes in Adriatic larval fish identification possible presence of new Gobiidae - Buenia massutii Kovacic, Ordines, and Schliewen, 2017, was noticed. Till now, occurrence of this species was restricted only to the Western Mediterranean and to the neighbouring part of the Atlantic Ocean.