This study presents primary observations of the natural diet of two endemic fishes, Delminichthys ghetaldii and Telestes dabar, along with an examination of their niche overlap. The feeding habits of these species were analyzed based on a dataset comprising 115 specimens collected from five karst poljes during the year 2018. Statistical analyses, including one-way ANOVA and Tukey’s HSD post-hoc testing, were employed to discern significant differences in body size and weight among the five populations of Delminichthys ghetaldii. Numeric indices such as numerical abundance, weight percentage of abundance, and frequency of occurrence, alongside a composite index (IRI - index of relative importance), were applied to elucidate the feeding strategy of these species. The diversity of diet and poljes utilization was assessed using Simpson’s diversity index, while predation selectivity was analyzed through the electivity index. Considerable overlap in the diet of Delminichthys ghetaldii was observed among the five poljes, as well as in the overlap between these two species. The findings of this study indicate that Delminichthys ghetaldii exhibits a zoophagous planktivorous diet, i.e. carnivorous, while Telestes dabar demonstrates a phytofagous planktivorous diet, i.e. herbivorous.

The primary objectives of this study were to advance understanding of the morphological intricacies exhibited by the endemic fish species Delminichthys ghetaldii, , commonly known as the Trebinje minnow, and to determine intraspecific morphological variability. The study involved the examination of 76 mature specimens collected since 2018 from five distinct karst fields located within the Dinaric region of Eastern Herzegovina, Bosnia and Herzegovina. A comprehensive analysis of 22 morphometric and 8 meristic characteristics was conducted to unravel the underlying patterns of variation. Discriminant function analysis was employed for the thorough investigation of the morphometric traits, whereas canonical correspondence analysis was applied to scrutinize the meristic traits. The discriminant function analysis yielded noteworthy outcomes, revealing substantial differentiations across 17 morphological characteristics within samples from diverse karst fields. Furthermore, it revealed notable dissimilarities in four morphometric characteristics when data including both male and female specimens were examined. Remarkably, these analyses showed that Delminichthys ghetaldii specimens inhabiting the Popovo karst field exhibit significant morphological disparities compared to those in the other fields. Conversely, individuals from the Fatni & ccaron;ko karst field showed a pronounced morphological affinity with their counterparts from the Mokro karst field. Intriguingly, a resemblance in morphometric characteristics was noted between Delminichthys ghetaldii inhabitants of the Dabarsko karst field and those from the Ljubomirsko karst field. The assessment of osteological meristic characteristics across samples from the five distinct karst fields, as well as the differentiation between male and female specimens, did not reveal any statistically significant distinctions.

Chondrichthyans are considered a highly threatened marine species, due both to the intense fishing pressure they have experienced in the world's Oceans over several decades, and other threats, such as habitat loss, climate change and marine pollution. A rapid decline in their populations could trigger significant negative changes in marine ecosystems, highlighting the need for improved conservation measures. This study analyzes the current state of this group in the waters of Montenegro (in the southeastern Adriatic Sea). The first national checklist is provided here, comprising of 44 species, with information on their occurrence frequencies in Montenegrin fishery catches. The dataset used consists of 1469 records obtained from 281 field samplings conducted as part of the official monitoring of commercial fisheries (DCF-DCRF) as well as 1222 records derived from citizen science. The latter contributed significantly in documenting a greater number of species, particularly those considered threatened or rare in the region, and/or overlooked by DCF-DCRF monitoring. The frequency of species in Montenegrin catches is described based on the percentage of their records in the total number of records originating from local fisheries. The obtained results indicate that only 16% of the species recorded in Montenegro are commonly present in country's catches, while 66% are either rare or not observed in local fishery. The creation of the country's first checklist might contribute to overcoming drawbacks in national legislation and protection measures, notably by reporting the presence of endangered species in national marine waters.

and Telestes montenegrinus (Vuković, 1963) from River Morača, Montenegro.Also, the paper provides the first comprehensive data of LWRs for endemic species for Telestes montenegrinus for which no LWR information was available in Fish Base.Values of b parameter ranged from 2.613 to 3.343, while values of a parameter ranged from 0.004-0.038.The results of this study could provide some additional insight into the ecology of the species and useful information for fisheries management in the studied river.

The aim of this study was to determine the concentrations of 28 elements in the liver, kidney, muscle, and heart of a small Indian mongoose from Montenegro. Element concentrations were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). Significant differences in elemental concentrations between analyzed tissues were observed for Ag, Al, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, P, S, Se, and Zn. The concentrations of Ag, Fe, Mo, and S were significantly different between all analyzed tissues. Muscle tissue is characterised by higher concentrations of some macroelements (K, Mg, S) and liver tissue by higher concentrations of some trace elements (Fe, Mn, Mo, and Zn). Cardiac tissue could be the target organ for bioaccumulation of Ag and Se. The molar ratio Se:Hg was higher than 1 in all studied tissues. There were few significant differences between element concentrations in mongooses from three analyzed (Airport, Saline, Inland) groups. Significantly higher concentrations of Ag and Se were found in liver tissue of Inland mongooses compared to animals from Airport and Saline. There were few significant differences (Zn in liver and muscle, Fe in muscle) in element concentrations between females and males.

A pool of data already existing about D-loop, i.e., the Control Region (CR) haplotypes of the mitochondrial DNA (mtDNA) of brown trout, Salmo trutta Linnaeus, 1758, tentative Adriatic trout Salmo farioides Karaman, 1938, and tentative Macedonian trout, Salmo macedonicus (Karaman, 1924), and their reconstructed phylogeography makes a good starting point for resolving their evolutionary history. That includes the dating of particular events in it. The events have hitherto been dated using the method of a molecular clock. Various calibrations were applied for the mutation rate, owing to the incongruence between the time of divergence that various authors notified and general knowledge about events in geological history and the periods in which they occurred in the Mediterranean region. Since geological history events were mandatory for setting the scene for the evolutionary history of brown trout, the incongruence between them has questioned the molecular clock calibration’s validity. From results about both the phylogeography and phylogenetic relations between native haplotypes (both partial and whole CR sequences) and the population genetics that characterized particular populations, we calculated the time of divergence between haplotypes in the regions of the western part of the Balkans: Iron Gate broader area in eastern Serbia, continental Montenegro and south-eastern Serbia. The distinct status of adjacent populations was verified by frequencies of microsatellites’ alleles and the STRUCTURE analysis that examined the significance of differences between them. In particular, we examined the populations that were clearly separated either by physical barriers, such as a waterfall in eastern Serbia (e.g., the upper and lower River Rečka supplemented by nearby rivers Vratna and Zamna), or by underground drops in Montenegro (e.g., upper and lower River Zeta, and rivers Nožica and lower River Mrtvica as isolated counterparts). We used the so far most common substitution rate of 1% in a million years’ (MY) period. The divergence times we obtained were compared to the events known for the region from available geological history data. There was a fairly good congruence between the dating obtained by the molecular clock method and that by geological history where the advanced, i.e., modern haplotypes, were concerned. In contrast, the congruence was worse for dating of divergence when more ancient haplotypes were in question, being much better if the mutational rate would be decreased to lower rates. That supported results both from the Rate Correlation Test about the independence of evolutionary rates in different lineages of brown trout, and from the Molecular Clock Test, which revealed that the evolutionary rate throughout the phylogenetic tree is not equal. That implies a difference in the speed of evolution in them, which was likely slower and faster, in the ancient, pre-Pleistocene haplotypes and the advanced, Pleistocene ones, respectively. The setting of the variable, or non-linear (i.e., logarithmic) speed of evolving seems helpful, since the early cladogenesis with the dominance of mutations was most likely combined afterwards with the acting of other evolutionary mechanisms, especially of genetic drift in populations that passed through the bottleneck episodes of the abrupt decrease in population size during the unfavourable periods of their evolutionary history.

A comprehensive study of fish diversity, relative and absolute biomass of registered species in Zeta River, Montenegro was accomplished.The data were collected during 2019 from three major ecological sectors of the river.A total of 14 fish species were recorded.The highest relative and absolute biomass were recorded on the Lower Zeta -Bjelopavlićithe lower part of the watercourse.Data presented in this paper shows a dramatic decline in both, the abundance and biomass of trout species from this river.Although in the 2019 th river Zeta watercourse in Bjelopavlići Valley was proclaimed as a Park of Nature, we haven't detected any benefits for the fish species, especially for the salmonid ones and their abundance continued with decreasing trend.Most probably the bad practice of poaching with forbidden tools just continued no matter on newly proclaimed protection status.It is shown that proclaiming some area or river in the protected area of any level doesn't benefit to biodiversity if it is not followed with precise management plans and strict implementation.

Elasmobranchs are among the most endangered marine species nowadays and many of them are threatened with extinction. The Adriatic Sea represents the northernmost arm of the Mediterranean Sea and is an ecosystem affected with centuries-long exploitation of marine resources. The data presented here date from the period from June 2015 to September 2020 and describes occurrences of elasmobranchs, considered to be either rare or endangered by the Data Collection Reference Framework (DCRF) manual of the General Fisheries Commission for the Mediterranean and Black Sea (GFCM). The data were obtained primarily from the commercial fishing fleet of Montenegro, with some provided by recreational fishermen, and located in the South-Eastern Adriatic Sea (GSA 18). The data were gathered from official DCRF data, scientific surveys and citizen science. Nine species listed as either rare or endangered in the DCRF Manual were found to be present in catches, among which the blue shark Prionace glauca (Linnaeus, 1758) was the most frequently encountered species. There were also occurrences of 5 more shark species and 3 batoids. The greatest numbers of records were observed in pelagic longline fishery and recreational big game fishing.

Salmonids are an extensively hatchery-reared group of fishes that have been introduced worldwide mainly for their high commercial and recreational value. The Balkan Peninsula (south-eastern Europe) is characterised by an outstanding salmonid diversity that has become threatened by the introduction of non-native salmonids whose potential risk of invasiveness in the region remains unknown and especially so under predicted climate change conditions. In this study, 13 extant and four horizon non-native salmonid species were screened for their risk of invasiveness in the Danube and Adriatic basins of four Balkan countries. Overall, six (35%) of the screened species were ranked as carrying a high risk of invasiveness under current climate conditions, whereas under predicted conditions of global warming, this number decreased to three (17%). Under current climate conditions, the very high risk (‘top invasive’) species were rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta (sensu stricto), whereas under predicted climate change, this was true only of O. mykiss. A high risk was also attributed to horizon vendace Coregonus albula and lake charr Salvelinus namaycush, and to extant Atlantic salmon Salmo salar and brook trout Salvelinus fontinalis, whose risk of invasiveness, except for S. fontinalis, decreased to medium. For the other eleven medium-risk species, the risk score decreased under predicted climate change, but still remained medium. The outcomes of this study reveal that global warming will influence salmonids and that only species with wider temperature tolerance, such as O. mykiss will likely prevail. It is anticipated that the present results may contribute to the implementation of appropriate management plans to prevent the introduction and translocation of non-native salmonids across the Balkan Peninsula. Additionally, adequate measures should be developed for aquaculture facilities to prevent escapees of non-native salmonids with a high risk of invasiveness, especially into recipient areas of high conservation value.

The endangered European eel biological life cycle consists of five stages of metamorphosis: leptocephalus, glass eel, elver, yellow eel, and silver eel.Montenegro has limited data on biological and population parameters of glass eel e.g.accurate time and the number of migration waves, condition, rate of survival, recruitment success, etc.Since the early 1980s, the occurrence of glass eels in European waters has decreased significantly.Accordingly, after almost 25 years the first research was conducted on glass eel in the river Bojana (Montenegro).This study was done during the winter and spring of 2021 and 2022.Stage of pigmentation and condition were examined on 50 registered individuals of glass eel.Four pigmentation stages: VIA0, VIA1, VIA2, and VII were registered.Its biometric characteristics indicate that one migration wave was registered with the domination of stage VIA1.This research indicates the necessity of further research on the glass eel, as well as the threats they are facing in the river Bojana and another small river in the Adriatic catchment of Montenegro, with the aim of establishing the management plan for better protection conservation of this important but vulnerable species.

Alongside climate change, the introduction of non-native species (NNS) is widely recognized as one of the main threats to aquatic biodiversity and human wellbeing. Non-native species and biodiversity are generally low priority issues on the political agendas of many countries, particularly in European countries outside the European Union (EU). The objectives and tasks of this study were to address the policy regulation, education level, education practices, and socioeconomic perceptions of NNS in the Balkans. A questionnaire-based survey was conducted in Albania, Bosnia and Herzegovina, Montenegro, North Macedonia and Turkey (Balkan EU candidate and potential candidate members), in Croatia and Greece (Balkan EU Member States) and Italy (non-Balkan EU Member State). The EU Alien Regulation (1143/2014) concerning NNS is implemented in EU Member States and Montenegro, whereas Albania, Bosnia and Herzegovina and Turkey have not reported specific policy regulations for NNS. Permanent monitoring programmes specifically designed for NNS have not yet been established in the EU Member States. Most countries tackle the issue of NNS through educational activities as part of specific projects. Education level is indicative of the implementation of NNS policy regulation, and efforts are needed for the proper development of relative study programmes. Public awareness and educational preparedness concerning NNS in the Balkans were identified as poor. Strong programmes for management and education should be developed to increase public awareness to prevent further biodiversity losses in the Balkan region.

Morphological and elemental composition of otoliths are a promising tool for fish stock identification. In this regard, European eel has not been sufficiently researched. The aim of this study was to determine otolith shape index values and microchemistry composition of 14 elements in otoliths of European eel between riverine and lacustrine stocks from the Adriatic Basin in Croatia and Montenegro. In terms of morphometry, the shape indices, form factor and circularity of the sagittal otolith were statistically different between lacustrine and riverine stocks. The European eel is considered to have a small otolith relative size. Canonical variate analysis indicated no statistical differences among the concentrations of trace elements in sagittal otoliths between riverine and lacustrine stocks. However, constrained redundancy analysis suggested a stronger relationship of width, total length, females and the silver stage with the Sr/Ca, Cr/Ca, Ba/Ca and K/Ca ratios of specimens from riverine than lacustrine habitats. Gender and stage dependent variations showed that females were better indicators of relationships between microchemistry composition and intrinsic factors. In conclusion, form factor and circularity of the sagittal otolith was able to distinguish between European eel stocks from different habitats. Also, it seems that the European eels' otolith fingerprint is homogenous, species specific and independent of ecological conditions.

The diversity of native trout fish Salmo spp. comprises a variety of nominal taxa in Serbia, Montenegro, and Bosnia and Herzegovina. Recent mapping of the resident trout populations detected the presence of brown trout Salmo trutta (sensu stricto) of the Atlantic (AT) mtDNA lineage introduced into populations of both tentative Danubian trout Salmo labrax and of tentative Adriatic trout Salmo farioides belonging to the Danubian (DA) and Adriatic (AD) mtDNA lineages, respectively. Introduction of the tentative Macedonian trout Salmo macedonicus of the AD lineage was also detected in a native population of the tentative S. labrax. In almost all recipient nonmigratory trout populations, a cross-breeding between native and introduced trout was detected by heterozygosity in either only the LDH-C nuclear locus or the LDH-C and specific microsatellite loci. The only exception was a population where both resident and migratory, lake-dwelling individuals of the tentative Adriatic trout spawned in a downstream section of a stream in Montenegro, as no microsatellite alleles of Atlantic brown trout that had been introduced upstream were detected. The occurrence of cross-breeding between Adriatic and brown trout was evident in the isolated, upstream section. It appears that migrating, lake-dwelling Adriatic trout in combination with their resident, stream-dwelling conspecifics suppress the introgression of genes from those situated upstream. In this regard, consideration should be given to the occurrence of the migratory brown trout in the Danube River at the broader Iron Gate Gorge area. They migrate in late summer and early fall from the Iron Gate One reservoir to the lower sections of tributaries devoid of any trout fish. However, some of these streams house very special native trout of the DA lineage in their short-extending upper sections. These native trout populations are, so far, still out of contact with the reservoir-dwelling trout. However, given the resilience of trout and their migratory life history, the outcome of this introduction could be deleterious for those native fish that are very precious in the conservation sense.

This study examined the relationship between the sagittal otolith morphometric variables (length, height and weight) and body growth of the European eel. Eels that were studied ranged in total length from 11.2 to 79.5 cm. The relationships between the sagittal otolith variables and fish somatic growth were described with a non-linear function. The resulting coefficients of determination \((r^2)\) ranged from 0.782 to 0.914. The variable most strongly related to fish size was found to be the sagittal otolith length (OL) with 91.4 % of the variability. The results of this study provide the first comprehensive data regarding the relationship between the sagittal otolith morphometric variables with the body length of Anguilla anguilla.