The Lower Danube River-Danube Delta-North West Black Sea: A pivotal area of major interest for the past, present and future of its fish fauna--A short review

Spatiotemporal variation in fish species distribution and abundance in the Vaishav stream, Kashmir Himalaya-India

Exploring the intricate dynamics of aquatic ecosystems present study investigates the spatio-temporal variations in the ecological parameters of the fish community within the Vaishav stream, Kashmir Himalayas. Monthly field investigations were conducted at three distinct sites (SI, SII & SIII) throughout the four seasons (winter, spring, summer, autumn) from November 2019 to October 2020. The findings encompass a total of 630 specimens belonging to 11 fish species, three orders Cypriniformes, Siluriforms and Salmoniformes and four families including Cyprinidae, Nemachelidae, Siluridae and Salmonidae were reported from the study sites. Among collected specimens, Cypriniformes were dominant with nine species followed by order Siluriformes and Salmoniformes with one species each. Out of eleven fish species, six fish species belongs to family Cyprinidae, three to Nemachelidae, one to Siluridae and Salmonidae each. The analysis, employing non-metric multidimensional scaling (NMDS), Principal component analysis (PCA), Analysis of similarity (ANOSIM) and Per-mutational multivariate analysis of variance (PERMANOVA) on fish abundance data highlighted significant differences among the various sites but not across seasons. The results unveil a diverse occurrence and distribution pattern of fishes from upstream to downstream. Furthermore, diversity metrics confirm higher diversity index values downstream, indicating a more conducive environment for fish survival. Jaccard's index reveals greater similarity in fish fauna between site-II and site-III than site-I and site-III in terms of overlap of fish species composition. The study concludes that anthropogenic activities in the stream catchment area have led to a reduction in fish diversity and abundance, with landscape features significantly influencing fish abundance in this unique Himalayan ecosystem.

Ecological study on helminths of three species of Gobiidae from the Danube River, Bulgaria

A total of 72 specimens of Babka gymnotrachelus (Kessler, 1857), Neogobius fluviatilis (Pallas, 1814), and Neogobius melanostomus (Pallas, 1814) from four sampling sites along the Bulgarian section of the Danube River (Kudelin, Novo selo, Koshava, and Kutovo), Northwestern Bulgaria were submitted to ecologohelminthological investigation. During the examination 6 species of helminths have been identified from 3 classes: Trematoda (Nicolla skrjabini (Iwanitzky, 1928) Dollfus, 1960), Acanthocephala (Acanthocephalus anguillae (Müller, 1780) Lühe, 1911; Acanthocephalus lucii (Müller, 1776) Lühe, 1911; Pomphorhynchus laevis (Zoega in Müller, 1776) Porta, 1908) and Nematoda (Contracaecum sp., Eustrongylides excisus Jägerskiöld, 1909). Ecological indices of the established endohelminth species were tracked. The four sampling sites from the Danube River are new habitats for the discovered endohelminth species of racer goby, monkey goby, and round goby. The three goby species are new host records: B. gymnotrachelus and N. fluviatilis for Ac. lucii; N. melanostomus for Ac. lucii, Ac. anguillae and Contracaecum sp. New species of helminths are found in the helminth fauna of the three studied species of gobies from the Danube River and the river basin (Ac. lucii of N. fluviatilis) and in Bulgaria (Ac. lucii of B. gymnotrachelus; Ac. lucii, Ac. anguillae and Contracaecum sp. of N. melanostomus). The pathogenic species helminths for the fish and humans are found.

Dietary Effects of Probiotic Lactobacillus casei on Some Immunity Indices of Common Carp (Cyprinus carpio) Exposed to Cadmium

The present study investigated the effect of feeding common carp with Lactobacillus probiotic supplement on growth, blood indices, and immunity of serum and mucus exposed to cadmium. A total of 250 common carp with an average weight of 15 ± 0.62 were divided into three groups: fish without probiotics, and fish with two levels of probiotic. At the end of a 42-day feeding period, 50% of the lethal concentrations of cadmium were exposed for 14 days and blood and immune indices of serum and mucus were measured. The results showed that growth indices, blood indices, and serum and mucus immunity were significantly different from the control group (P < 0.05). Finally, this study showed probiotics could improve the decreasing effect of cadmium in BWI and PBWI indices and the additive effect of cadmium in FCR and ALT. Probiotic was also able to completely improve the decreasing effect of cadmium on lymphocyte indices and the additive effect of cadmium on ALP and AST and monocyte.

Freshwater as a Sustainable Resource and Generator of Secondary Resources in the 21st Century: Stressors, Threats, Risks, Management and Protection Strategies, and Conservation Approaches

This paper is a synthetic overview of some of the threats, risks, and integrated water management elements in freshwater ecosystems. The paper provides some discussion of human needs and water conservation issues related to freshwater systems: (1) introduction and background; (2) water basics and natural cycles; (3) freshwater roles in human cultures and civilizations; (4) water as a biosphere cornerstone; (5) climate as a hydrospheric 'game changer' from the perspective of freshwater; (6) human-induced stressors' effects on freshwater ecosystem changes (pollution, habitat fragmentation, etc.); (7) freshwater ecosystems' biological resources in the context of unsustainable exploitation/overexploitation; (8) invasive species, parasites, and diseases in freshwater systems; (9) freshwater ecosystems' vegetation; (10) the relationship between human warfare and water. All of these issues and more create an extremely complex matrix of stressors that plays a driving role in changing freshwater ecosystems both qualitatively and quantitatively, as well as their capacity to offer sustainable products and services to human societies. Only internationally integrated policies, strategies, assessment, monitoring, management, protection, and conservation initiatives can diminish and hopefully stop the long-term deterioration of Earth's freshwater resources and their associated secondary resources.

Anti-Depressant Fluoxetine Hampers Olfaction of Goldfish by Interfering with the Initiation, Transmission, and Processing of Olfactory Signals

The ubiquitous presence of fluoxetine (FLX) in aquatic environments poses great threat to fish species. However, little is known about its deleterious impacts on fish olfaction. In this study, the olfactory toxicity of FLX at environmentally realistic levels was assessed by monitoring the behavioral and electroolfactogram (EOG) responses to olfactory stimuli with goldfish (Carassius auratus), and the toxification mechanisms underlying the observed olfaction dysfunction were also investigated. Our results showed that the behavioral and EOG responses of goldfish to olfactory stimuli were significantly weakened by FLX, indicating an evident toxicity of FLX to olfaction. Moreover, FLX exposure led to significant alterations in olfactory initiation-related genes, suppression of ion pumps (Ca²⁺-ATPase and Na⁺/K⁺-ATPase), tissue lesions, and fewer olfactory sensory neurons in olfactory epithelium. In addition to altering the expression of olfactory transmission-related genes, comparative metabolomic analysis found that olfaction-related neurotransmitters (i.e., l-glutamate and acetylcholine) and the olfactory transduction pathway were significantly affected by FLX. Furthermore, evident tissue lesions, aggravated lipid peroxidation and apoptosis, and less neuropeptide Y were observed in the olfactory bulbs of FLX-exposed goldfish. Our findings indicate that FLX may hamper goldfish olfaction by interfering with the initiation, transmission, and processing of olfactory signals.

Impact of hydrotechnical construction on aquatic ecosystems of the Kiliia branch of the Danube Delta

Resumption of shipping in the Bystryi branch in the Ukrainian part of the Danube Delta, one of the largest aquatic-wetland areas of Europe and the world, has made it necessary to control the anthropogenic impact on the neighboring water areas of the Danube Biosphere Reserve. The objective of the study was comparing the compositions and structure of phytoplankton, microphytobenthos, macrophytes, benthic invertebrates and ichthyofauna of the mouth area of the Bystryi branch with such communities of the mouths of the branches Vostochnyi, Tsyhanka and Starostambulskyi, which are situated in the protected zone and characterized by limited anthropogenic activity. We also determined the correspondence of the descriptors of biotic groups to the categories of the ecological status according to the Water Framework Directive of the EU. The studies were performed in the autumn and summer periods in 2020–2021. We recorded 367 species of animals and plants, the richest biodiversity was seen for the biota of the Bystryi branch – 250 species, and 180–231 species of hydrobionts were found in the undisturbed mouths. We determined 25.3% of shared species for the water areas, and therefore high values of similarity of the species compositions according to Bray-Curtis (47.5% to 81.5%). We determined no significant differences between the groups of the mouths of the examined branches according to most indicators of taxonomic and ecological structure. As the descriptors of ecological status, we chose assemblage indices of phytoplankton and microphytobenthos, which are based on ratios of biomass of functional groups of algae, and also the Macrophyte Biological Index for Rivers, saprobic index of Zelinka & Marvan and Biological Monitoring Working Party Index of Benthic Invertebrates and Representation of Species of Ichthyfauna according to vulnerability to actions of environmental factors. We determined that the range of descriptors of phytoplankton and microphytobenthos corresponded to the “high” ecological status category, such of macrophytes and benthic invertebrates to “good”, and such of ichthyofauna varied “high” to “good”. In general, all the mouth areas were characterized by “good” ecological status. Similarities of the species composition and the structure of biotic communities of the mouths of the studied branches of the delta indicate the absence of negative impact of the deepwater shipping on adjacent ecosystems, which may be related to the peculiarities of reactions of groups in the water areas with natural stress, as well as local impact of the hydrotechnical construction.

Invasive Alien Species of Benthic Macroinvertebrates and Fish in the Bulgarian Sector of the Danube River—Results of the Joint Danube Survey 4 (JDS4)

The aim of this study was to assess the status of aquatic invasive alien species (IAS) in the shoreline zone of the Bulgarian sector of the Danube River, Danube tributaries, and adjacent standing water bodies in the frame of the Joint Danube Survey 4 (JDS4). Seven benthic macroinvertebrates and seven fish IAS were identified. The crayfish Faxonius limosus was frequently found and abundant in the tributaries. The mussels Corbicula fluminea, Dreissena rostriformis bugensis, and Sinanodonta woodiana dominated in the Danube River and the middle and lower reaches of the tributaries, while the fish Carassius gibelio, Perccottus glenii, and Lepomis gibbosus were most abundant in the standing water bodies. The integrated biocontamination estimated by taxonomic groups (crayfish, molluscs, and fish), sampling methods, and type of water bodies ranged from moderate in the shoreline zone of the Danube River, through moderate to high in the canals and lakes, to severe in the Danube tributaries and the reservoirs. The results demonstrate the importance of IAS in the assessment of the ecological status/potential of the water bodies in the DRB. The comprehensive evaluation of the aquatic IAS pressure will provide valuable information and support for the implementation of the national and EU IAS and water policies in the DRB.

Fish Species Composition, Distribution and Community Structure in Relation to Environmental Variation in a Semi-Arid Mountainous River Basin, Iran

We analyzed spatial variation in fish species richness and community composition in the Karun River basin, Iran. Knowledge about fish diversity in the basin is incomplete and varies widely along spatial and temporal scales: The Karun is the longest river in Iran (950 km) with the largest drainage area (about 67,000 km²). Fish samples were collected from 54 sites from July through August 2019 using a backpack electro-fisher. Physico-chemical and habitat parameter data collected at each site included pH, conductivity (μS/cm), dissolved oxygen (mg/L), water temperature (°C), turbidity (NTU), stream width (m), stream depth (m), water velocity (m/s) and elevation (m). In total, 37 species were collected (5241 individuals weighing 110.67 kg). The species collected represented 12 families and 27 genera. A total of 13 endemic species (35.14%), 16 native species (43.24%), and eight non-native species (21.62%) were recorded. Diversity indices were calculated and used to measure the spatial variation in community composition. Relationships between native and endemic species assemblage structure and environmental descriptors were assessed using canonical correspondence analysis (CCA). The first two axes of the canonical correspondence analysis explained 62.57% of the variation in the data. Of the nine environmental descriptors analyzed, eight significantly affected species distribution; however, electrical conductivity and elevation were most influential. Our study provides up-to-date status information on the distribution of freshwater fishes in the Karun River basin. This information is essential for developing conservation and management strategies to support the long-term sustainability of fish populations in the Karun River basin.

Coştei Hydrographic Diversion Node, a Historical Environment Quality and Biological Resources Accessibility Game Changer; Anthropogenic Induced Problems and Sustainable Solutions ‒ An Ichthyologic Perspective

26 fish species were affected by the Coştei historical diversion hydrotechnical system build in 1758. In order to mitigate the negative effects produced by this hydrotechnical work on the fish, a migration system, of nature-like meandering by pass type was proposed. The dimensions of this channel and the slope of about 2% allow fish, and other aquatic organisms to move upstream and downstream of the spillway.

Emerging and Persistent Pollutants in the Aquatic Ecosystems of the Lower Danube Basin and North West Black Sea Region—A Review

The tremendous impact of natural and anthropogenic organic and inorganic substances continuously released into the environment requires a better understanding of the chemical status of aquatic ecosystems. Water contamination monitoring studies were performed for different classes of substances in different regions of the world. Reliable analytical methods and exposure assessment are the basis of a better management of water resources. Our research comprised publications from 2010 regarding the Lower Danube and North West Black Sea region, considering regulated and unregulated persistent and emerging pollutants. The frequently reported ones were: pharmaceuticals (carbamazepine, diclofenac, sulfamethoxazole, and trimethoprim), pesticides (atrazine, carbendazim, and metolachlor), endocrine disruptors—bisphenol A and estrone, polycyclic aromatic hydrocarbons, organochlorinated pesticides, and heavy metals (Cd, Zn, Pb, Hg, Cu, Cr). Seasonal variations were reported for both organic and inorganic contaminants. Microbial pollution was also a subject of the present review.

Endocrine-Disrupting Compounds: An Overview on Their Occurrence in the Aquatic Environment and Human Exposure

Endocrine-disrupting compounds (EDCs) as emerging contaminants have accumulated in the aquatic environment at concentration levels that have been determined to be significant to humans and animals. Several compounds belong to this family, from natural substances (hormones such as estrone, 17-estradiol, and estriol) to synthetic chemicals, especially pesticides, pharmaceuticals, and plastic-derived compounds (phthalates, bisphenol A). In this review, we discuss recent works regarding EDC occurrence in the aquatic compartment, strengths and limitations of current analytical methods used for their detection, treatment technologies for their removal from water, and the health issues that they can trigger in humans. Nowadays, many EDCs have been identified in significant amounts in different water matrices including drinking water, thus increasing the possibility of entering the food chain. Several studies correlate human exposure to high concentrations of EDCs with serious effects such as infertility, thyroid dysfunction, early puberty, endometriosis, diabetes, and obesity. Although our intention is not to explain all disorders related to EDCs exposure, this review aims to guide future research towards a deeper knowledge of EDCs’ contamination and accumulation in water, highlighting their toxicity and exposure risks to humans.

Innovative On-Site Adapted System for Fish Migration with Flow Divider and Glass Collector Basin

The authors designed a new site-adapted fish passage system for upstream and downstream migration of small and large fish on the urban sector of the Bistriţa River. The longitudinal connectivity of this lotic system is interrupted by numerous transversal hydrotechnical works (weirs). This proposed system was designed to facilitate fish migration, promote fish recolonization of upstream and downstream habitats, allow the expansion of fish range, and increase spawning potential. All components of the proposed system are attached to a concrete girder located to the right stream bank, except a glass basin that is submerged in the riverbed. The positioning of the system in this girder ensures its resistance to high water events, while offering safe passage for fish in both directions.

Species and Thallus Structure Diversity of Chlorophyta in Shore Platform of Dwarka (Gujarat Coast, India)

Present study shows the species and thallus structure diversity of Chlorophyta in shore platform of Dwarka, Gujarat Coast. Chlorophyta were surveyed based on systematic random sampling for two years: April 2013 to April 2015. Total 27 species of Chlorophyta were identified through intensive fieldwork survey based on line transect and quadrate based methods. This study identifies four orders, nine families, 13 genera and 27 species among the green macroalgae population inhabiting the rock shore platform of Dwarka. Total 27 species of Chlorophyta have been found with major nine thallus types and 19 sub types of thallus structure. Ramiform and filamentous types of thallus structure are most common in this study.

Range Map and Distribution of Luciobarbus barbulus Heckel 1847 in the Tigris and Euphrates River Basins

Luciobarbus barbulus Heckel, 1847 was described from water bodies around Shiraz and the Qara Aqaj River, one of the main rivers in Shiraz City, Iran. In the present study localities, a geographical range map of Luciobarbus barbulus and new data on the present status of this species are presented. In our latest sampling we assessed for the first time the presence of this species in the Lesser Zab River where no specimen had been collected in the past on this part of the river. The detailed distribution of Luciobarbus barbulus, based on the captured specimens, and literature records of this species are mentioned.

Preliminary investigation of lower Danube pollution caused by potentially toxic metals

The current study aims to assess the pollution status of the European river-sea system lower Danube River-Danube Delta-North West Black Sea, through an integrated analysis of metal concentrations in water, sediments and fish community. The Danube flows through numerous industrial cities and receives a significant amount of pollutants due to the reception of urban and industrial emissaries, as well as agricultural land runoff. Samples of water, sediments and fish (10 species) were collected from 7 representative sites along Danube River, Danube Delta and Black Sea shore. For the analysed fish species, potentially toxic and essential elements (Pb, Cd, As, Cu, Fe, Zn, Mg, Ca, Na, K) from muscle and liver samples were measured and discussed. Measurement of elements and other environmental quality parameters were determined for water and sediments. The Black Sea area, represented by S6 and S7, received sediments from Danube with the lowest concentrations of Cd (0.05 ± 0.01 μg g^-1, respectively 0.01 ± 0.001 μg g^-1), Pb (3 ± 0.03 μg g^-1, respectively 2 ± 0.03 μg g^-1), As (2 ± 0.02 μg g^-1, respectively 1.4 ± 0.3 μg g^-1), Ni (8.9 ± 0.1 μg g^-1, respectively 5.2 ± 0.2 μg g^-1), Cr (8 ± 0.7 μg g^-1, respectively 5 ± 0.2 μg g^-1), Cu (3 ± 0.1 μg g^-1, respectively 2 ± 0.04 μg g^-1), Fe(6 ± 0.3 μg g^-1, respectively 3 ± 0.1 μg g^-1) and Zn (0.03 ± 0.003 μg g^-1, respectively 0.017 ± 0.001 μg g^-1). These results suggest that the Danube Delta system plays an important role in filtering the pollutants. Based on the biota and water analysis, there was no correlation observed between Cd, respectively Pb concentration in the environment and fish body (Person Coef. = -0.02 in muscle tissue and -0.01 in liver tissue, respectively Pearson Coeff. = -0.06 in muscle tissue and 0.1 in liver tissue). Cadmium remained an active element in the pollution of the Danube area (S1 and S2), with high concentration in the water matrix (0.14 ± 0.02 μg L^-1, respectively 0.05 ± 0.01 μg L^-1) and fish muscle (0.15 ± 0.03 μg g^-1f.w. in C. carpio - S2). This fact was confirmed by several other studies.

Adding the Mureş River Basin (Transylvania, Romania) to the List of Hotspots with High Contamination with Pharmaceuticals

Background: The Mureș River Basin is a long-term heavily polluted watershed, in a situation of climate changes with decreasing water flow and related decreasing dilution capacity. Here, a mixture of emerging pollutants such as pharmaceuticals were targeted to reveal potential risks regarding the natural lotic ecosystems. Due to the continuous discharge into the environment, pharmaceuticals are gaining persistent organic pollutant characteristics and are considered emerging pollutants. Based on the hazard quotient, this research highlights the dangerous concentrations of carbamazepine, ibuprofen, furosemide, and enalapril in river water. Results: High levels of four pharmaceutical compounds (carbamazepine, ibuprofen, furosemide, and enalapril) and some of their derived metabolites (enalaprilat, carboxyibuprofen, 1-hydroxyibuprofen, and 2-hydroxyibuprofen) were reported in our study in the Mureș River Basin. Overall, pharmaceutical concentrations were found to be highest in the wastewater treatment plant (WWTP) effluent, median downstream of the WWTP, and lowest upstream of the WWTP, as was expected. For all pharmaceutical compounds tested, we recorded concentrations above the limit of quantification (LOQ) in at least one of the sites tested. Carbamazepine exhibited the highest mean values upstream, downstream, and at the WWTP. As expected, the highest concentrations for all the studied pharmaceutical compounds were detected in the WWTP effluent. All Hazard Quotient (HQ) values were below one (on a logarithmic scale in base 10), with the highest values in the WWTP and the lowest in the river upstream of the WWTP. The HQ intervals were in the same range for furosemide, carbamazepine, and ibuprofen at each of the three different sites: upstream WWTP effluent, and downstream. The interval for enalapril stands out as having the lowest HQ at all three sites. Conclusions: Based on these results, the large and complex hydrographical system Mureș River Basin was transformed from a grey area, with little information about pharmaceutical contamination, to a hotspot in terms of contamination with emerging pollutants. Pharmaceutical compound concentrations were found to be the highest in WWTP effluents. The WWTP effluent concentrations were among the highest in Europe, indicating that treatment plants are the primary source of water pollution with pharmaceuticals compounds. The detected levels were higher than the safety limit for carbamazepine and ibuprofen. The determined HQ values imply that the measured levels do pose a threat to the environment for the studied pharmaceuticals. Based on the obtained results, human communities can assess, monitor, predict, and adapt in time to these already-present regional challenges and risks for sustainable use of natural resources, including water and associated products and services.

Bioaccumulation of persistent organic pollutants in the gonads of Barbus barbus (Linnaeus, 1758)

Maps with grey or even white spaces are still present in spite of the fact that persistent organic pollutants (POPs) are at the forefront of research in aquatic toxicology and environmental safety. This is also the case for the Mureș River basin. The intensive use of industrial substances such as polychlorinated biphenyls (PCBs) and pesticides such as organochlorine compounds (OCPs) has caused global contamination of the aquatic environment. In our study we have found very high concentrations of both PCBs (2110-169,000 ng/g lipid weight ΣPCB, 1950-166,000 ng/g lipid weight ΣPCB₇) and OCPs (1130-7830 ng/g lipid weight ΣDDT, 47.6-2790 ng/g lipid weight ΣHCH, 5.53-35.6 ng/g lipid weight ΣChlordane, and 6.74-158 ng/g lipid weight HCB) in the gonad tissue of Barbus barbus (Linnaeus, 1758) males and females. Contrary to most studies where the weight, length, and lipid percentage are positively correlated with the concentration of POPs from different tissue types, we observed a downward trend for the lipid normalized concentrations of some pollutants in gonads while these indices were actually increasing. The decrease of lipid normalized POPs with the increase of CF and lipid percentage may be due to the fact that individuals are eliminating hard and soft roes every year during reproduction which could mean that some quantities of pollutants are also eliminated along with the hard and soft roes. The high POPs concentrations found in our study should be a needed wakeup call for environmentalists and a starting point in developing monitoring and management measures for these pollutants.

Is Peniculus Fistula Fistula Nordmann, 1832 Reported On Coryphaena hippurus Linnaeus, 1758 From Turkey? Updated Data with Further Comments And Considerations

53 striped surmullet, Mullus surmuletus Linnaeus, 1758 (Teleostei, Mullidae), were collected from the Marmara Sea, Turkey and examined for metazoan parasites in July 2017. The parasitic copepod, Peniculus fistula fistula Nordmann, 1832 (Pennellidae), was collected from all the hosts, both on fins and body surface. This is the second report of this copepod in Turkish marine waters. Although Peniculus fistula fistula was reported for the first time on Coryphaena hippurus Linnaeus, 1758 by Öktener (2008), there was an indefiniteness and doubt about the occurrence of this parasite. This study aimed to confirm occurrence of Peniculus fistula fistula in Turkey and to present revised host list with comments.

Gobio Genus Species Integrated Management System – Târnava Rivers Study Case (Transylvania, Romania)

The lotic habitats quality indicative congeners species Gobio gobio, Gobio kessleri and Gobio albipinnatus populations’ dynamic in time (2004-2019) and space revealed a decreasing trend in these rivers ecological status. The ADONIS:CE tool has been used to build a backing management system model, based on these indicative fish species habitat needs, indicators for favourable conservation status, pressures and threats. This management system implementation in the field will favour the amelioration of lotic habitats and the ecological status recovering of two of the local fish species of conservative interest (G. kessleri and G. albipinnatus).

Wetlands and their Fish Diversity in Assam (India)

Water is indispensably important for sustenance of life. Wetlands serve as potential reservoirs of water which also harbour coveted bioresources, which sustain animal life. Fish is a potential bioresource for nutrition and offer work places for people. The Asian continent has innumerable wetlands with the Indian sub-continent portraying myriads of wetlands of different kinds, including perennial wetlands (locally called “Beel” or “Taal”), seasonal floodplain wetlands (“Haor”) and river-formed oxbow wetlands (“Anua”). In addition to playing a pivotal role in providing nutrition and work places to the people, wetlands also play a significant role in flood management, in regulating biogeochemical cycles, and above all, perhaps, in the rehabilitation of the innumerable fish stocks.

Morphology of the Genus Gymnocephalus (Pisces) from the Lower Danube River

The current study completed the information regarding the phenotypic variability in the Danube ruffe (Gymnocephalus baloni). We also assessed the phylogenetic relationship of G. baloni with the other two species of the genus Gymnocephalus from the Lower Danube River.

Ten morphological characters were the most useful together for discriminating between G. baloni and G. cernua from the Lower Danube River. In addition, we found a more streamlined body shape in G. baloni compared with the described holotype, which could be in connection with fish phenotypic response to ecological characteristics of the Lower Danube River.

Technical Solutions to Mitigate Shifting Fish Fauna Zones Impacted by Long Term Habitat Degradation in the Bistra Mărui River – Study Case

The Bistra Mărului River fish fauna has been severely impacted by man-made activities, especially through longitudinal fragmentation, over the past 40 years. Fish fauna monitoring revealed structural changes and technical methods have been proposed, in order to restore the natural connectivity and the conservation of fish species. Benefits should accrue for key species: Salmo trutta fario, Cottus gobio, Thymallus thymallus, Eudontomyzon danfordi, Eudontomyzon vladykovi, Gobio uranoscopus, Barbus meridionalis, and Condrostoma nasus.

Using Fishers Knowledge in Community Based Fisheries Management in the River Nun Estuary, Niger Delta

A study of fishers’ knowledge in community based fisheries management practices in the Nun River estuary were conducted to assess the contribution of fishers’ knowledge to fisheries resources conservation. The total number of fishers that operated in the area were 390, and 221 fishers were interviewed based on a minimum of 10 years fishing experience using the socio-ecological approach. The laws introduced are banned on the use of mesh size less than five cm and banned on chemical fishing. Fishers caught using chemicals to fish were arrested and handed over to the police for prosecution. The management method has enhanced conservation of fisheries’ resources, which is a major source of livelihood for the people. It is therefore pertinent to introduce community based laws to check over exploitation of fisheries’ resources in fishing communities in the Niger Delta.

Upper Caraş River (Danube watershed) fish populations fragmentation – technical rehabilitation proposal

We propose a technical solution for fish movement based on the flow of water over a spill threshold. Such barriers are common in the Danube system. The proposed system has a range of operating components which are easily detachable from the spill threshold, are resistant to corrosion and will not harm the fish. In fact, if designed to complement swimming abilities of target fish, it should provide adequate passage for both adults and juveniles. If implemented correctly, the design may offer a solution to help displaced fish recolonize upstream habitats.

Barbus meridionalis Risso, 1827 populations status in the Vişeu River basin (Maramureş Mountains Nature Park)

The ecological state of lotic ecosystems occupied naturally by Barbus meridionalis, in the Vişeu Basin within the Maramureş Mountains Natural Park, vary among good to reduced. The inventoried human activities which negatively influence the ecologic state of the Barbus meridionalis species habitats and populations are the organic and mining pollution, and poaching. The habitats with low and inadequate conditions created a reduced status of the Barbus meridionalis populations; the status of Barbus meridionalis populations is not so much affected in the cases of habitats of average to good condition. Barbus meridionalis is considered a relatively common fish species in the researched watershed despite the fact that its populations ecological status has decreased from 2007-2015, but the restoration potential in the area for improving this species status is high.

Trophic Relationships and Status of Reservoirs with and without Occurrence of Dreissena ssp. (Mollusca, Bivalvia) Built on Bulgarian Danube River Tributaries

The trophic status and relationships between Secchi depth transparency (SD) chlorophyll-a (CHL) and total phosphorus (TP) concentrations from nine non-infested and five infested areas with invasive alien species, Dreissena ssp. reservoirs, situated on the Bulgarian Danube River tributaries were studied. The trophic status index (TSI) values after Carlson (1977), and showed statistically significant differences for all three variables between infested and non-infested reservoirs. The three linear regression equations between SD × CHL, CHL × TP and SD × TP were statistically significant for the group of non-infested reservoirs, while in the infested reservoirs only the SDxCHL regression was statistically significant for P < 0.05. Our results showed that the Dreissena invasion destroyed the linear relationship between CHL × TP and SD × TP and seems to affects the accurate application of Carlson TSI.

Approaching the Potential of World Marine Fisheries

During the last 60 years, the world marine fisheries potential has been estimated between 22·106 tons and 1 400·106 tons.

However, there are no certain indications of when and with what probability such potential will be reached.

By fitting a logistic curve to the observed world marine catch, corrected for discards and illegal, unreported and unregulated fishing, here we calculated that such potential stands between 132·106 tons and 153·106 tons and might be achieved as soon as the year 2027, with 95% confidence.

Proposal to Achieve Floodplain Connectivity in Alțâna Sector on Hârtibaciu River (Transylvania, Romania)

The process of supplying water to the new anthropogenic wetland is achieved gravitationally, and the excess water in the wetland will be directed towards the Hârtibaciu River in a similar natural way. The fish and fauna of the Hârtibaciu River have a disrupted lateral connectivity due to its banks embanking including in the proximity of the Alţâna locality. The newly proposed anthropogenic wetland would improve habitat quality for the fish species of conservation interest, Rhodeus amarus (Bloch, 1782), and increase its population numbers. A new fish species, Chondrostoma nasus, was identified for the first time in the Hârtibaciu River.