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Humans play an integral role in biological invasions, from aiding introductions of alien species to experiencing their impacts and holding the ability to manage them. The importance of understanding the dynamics of stakeholders' perceptions on alien species is therefore increasingly recognized. In this study, we used anonymous online surveys to contrast recreational anglers' perceptions towards European flounder (Platichthys flesus, Linnaeus, 1758) in Iceland, where it is classified as a potentially invasive species, to the perceptions prevailing amongst recreational anglers in the species' native range. We furthermore explored potential temporal changes in the perception of Icelandic recreational anglers. Our results indicate that Icelandic recreational anglers have a highly negative perception towards the European flounder, while in its native range, recreational anglers have positive perceptions towards this species. In Iceland, we have furthermore detected a significant change towards less negative perceptions between the surveys administered in October 2019 and March 2023. Finally, we compared the results of the online surveys and novel, conservation culturomics tools to further explore stakeholder perceptions and public interest in Iceland. The comparison highlighted some limitations that should be considered when using culturomics in very small societies or for small languages. For example, the text mining approaches on newspaper articles and social media conservations detected neutral perceptions in the communication to the public and within the targeted stakeholder group via social media in contrary to the perceptions detected in the online surveys. Moreover, we detected short-term peaks in the public's interest in European flounder and potential drivers of those peaks using Wikipedia pageviews but Google Trends provided mixed and unreproducible results. Overall, our study highlights that stakeholders' perceptions towards an alien species as well as the public's interest in it vary over time and space, though the drivers of these changes are often difficult to identify. [ABSTRACT FROM AUTHOR]

Simple Summary: In order to reliably record pollution from microplastics within animals, indicators for a monitoring program must be found. For this purpose, we collected invertebrates, fish, and sediment cores at 10 sites along the Wadden Sea coast of Lower Saxony, Germany; determined the amount of microplastics; and made recommendations for potential bioindicator species, based on the sampling conditions and results. The species studied included lugworm (Arenicola marina), common periwinkle (Littorina littorea), blue mussel (Mytilus edulis), and European flounder (Platichthys flesus). In total, microplastics were detected in 88% of the specimens and in each sediment core sample. Regarding the polymer composition, eight different types of microplastic were identified. Based on the results, the species blue mussel and European flounder are recommended for microplastic monitoring in biota. Monitoring strategies are becoming increasingly important as microplastic contamination increases. To find potentially suitable organisms and sites for biota monitoring in the German Wadden Sea, we collected invertebrates (n = 1585), fish (n = 310), and sediment cores (n = 12) at 10 sites along the coast of Lower Saxony between 2018 and 2020. For sample processing of biota, the soft tissue was digested and the sediment samples additionally underwent a subsequent density separation step. Microplastic particles were identified using Nile red and fluorescence microscopy, followed by polymer composition analysis of a subset of particles via µRaman spectroscopy. All investigated species, sediment cores, and sites contained microplastics, predominantly in the morphology class of fragments. Microplastics were found in 92% of Arenicola marina, 94% of Littorina littorea, 85% of Mytilus edulis, and 79% of Platichthys flesus, ranging from 0 to 248.1 items/g. Sediment core samples contained MPs ranging from 0 to 8128 part/kg dry weight of sediment. In total, eight polymers were identified, predominantly consisting of polyethylene, polyvinylchloride, and polyethylene terephthalate. Considering the sampling, processing, and results, the species Mytilus edulis and Platichthys flesus are suitable species for future microplastic monitoring in biota. [ABSTRACT FROM AUTHOR]

Simple Summary: The European flounder (Platichthys flesus), which is closely related to the recently discovered Baltic flounder (Platichthys solemdali), is currently the third most commercially fished species in the Baltic Sea. The aim of this study was to obtain information on the current patterns of genetic diversity and the population structure of the European flounder and to verify whether the Baltic flounder is present in the southern Baltic Sea. Moreover, we aimed to verify whether the observed decline in the body condition indices of the species in the Baltic Sea might be associated with adaptive changes in its gene pool due to increased fishing pressure. The examined European flounder specimens displayed a high level of genetic diversity and represented a single genetic cluster. The applied molecular markers did not detect the presence of the Baltic flounder among the fish sampled from the studied area. Correlation analysis between genetic and morphological characteristics did not detect any signs of directional selection or density-dependent adaptive changes in the gene pool of the examined fish. The European flounder (Platichthys flesus), which is closely related to the recently discovered Baltic flounder (Platichthys solemdali), is currently the third most commercially fished species in the Baltic Sea. According to the available data from the Polish Fisheries Monitoring Center and fishermen's observations, the body condition indices of the species in the Baltic Sea have declined in recent years. The aim of the present study was to obtain information on the current patterns of genetic variability and the population structure of the European flounder and to verify whether the Baltic flounder is present in the southern Baltic Sea. Moreover, we aimed to verify whether the observed decline in the body condition indices of the species in the Baltic Sea might be associated with adaptive alterations in its gene pool due to increased fishing pressure. For this purpose, 190 fish were collected from four locations along the central coastline of Poland, i.e., Mechelinki, Władysławowo, the Vistula Lagoon in 2018, and the Słupsk Bank in 2020. The fish were morphologically analyzed and then genetically screened by the application of nineteen microsatellite DNA and two diagnostic SNP markers. The examined European flounder specimens displayed a high level of genetic diversity (PIC = 0.832–0.903, I = 2.579–2.768). A lack of significant genetic differentiation (Fst = 0.004, p > 0.05) was observed in all the examined fish, indicating that the European flounder in the sampled area constitutes a single genetic cluster. A significant deficiency in heterozygotes (Fis = 0.093, p < 0.05) and overall deviations from Hardy–Weinberg expectations (H-WE) were only detected in fish sampled from the Słupsk Bank. The estimated effective population size (Ne) among the sampled fish groups varied from 712 (Słupsk Bank) to 10,115 (Władysławowo and Mechelinki). However, the recorded values of the Garza–Williamson indicator (M = 0.574–0.600) and the lack of significant (p > 0.05) differences in Heq > He under the SMM model did not support the species' population size changes in the past. The applied SNP markers did not detect the presence of the Baltic flounder among the fish sampled from the studied area. The analysis of an association between biological traits and patterns of genetic diversity did not detect any signs of directional selection or density-dependent adaptive changes in the gene pool of the examined fish that might be caused by increased fishing pressure. [ABSTRACT FROM AUTHOR]

The objective of this study was to develop an integrative approach in ecotoxicology (from biomarkers to population genetics) to assess the ecological status of fish populations. Flounders (Platichthys flesus) collected after the spawning season in the heavily polluted Seine estuary were compared with the moderately polluted Bay of Douarnenez. The muscle energetic reserves were highly depleted in Seine vs. Douarnenez fish. The Seine fish displaying a reduced capacity to manage the oxidative stress and a higher energetic metabolism. An increase in the content of muscle membrane phospholipids (sphingomyelin, phosphatidylserine, free sterols) was detected in the Seine vs. Douarnenez fish. The data integration allowed to hypothesize relationships between membrane phospholipids, xenobiotic metabolism, bioenergetics, and antioxidant defence. The genetic diversity considering neutral markers was maintained in the heavily polluted Seine population compared with the Douarnenez population. Finally, we suggest that the high physiological cost of tolerance to toxicants in the Seine flounder population could compromise its capacity to respond in the future to an additional stressor like warming waters in shallow depth. Thus, this population could be submitted to an ecological risk.

Maritime trade and transportation of hazardous and noxious substances (HNS) have been increasing in European waters, augmenting the risk of accidental spills from ships or in harbours. Despite their reported toxicity and hazardousness, information on HNS levels in the aquatic environment is still lacking. Therefore, an assessment combining a chemical and a multi-biomarker evaluation on HNS contamination was done in NW Iberian estuaries of Rivers Minho, Lima and Douro using Platichthys flesus (flounder). Of the twenty-five HNS measured, fifteen were found in flounder liver and muscle, and a few in sediments, though at generally low levels. Principal component analysis produced a clear distinction among sites, with Douro River estuary arising as the most impacted. Oxidised proteins and antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase) were the biomarkers contributing to site discrimination. Correlations between biomarkers and HNS levels provided important baseline information for the study area and potential biological effects of HNS on this sentinel species.

The objective of this study was to develop an integrative approach in ecotoxicology (from biomarkers to population genetics) to assess the ecological status of fish populations. Flounders (Platichthys flesus) collected after the spawning season in the heavily polluted Seine estuary were compared with the moderately polluted Bay of Douarnenez. The muscle energetic reserves were highly depleted in Seine vs. Douarnenez fish. The Seine fish displaying a reduced capacity to manage the oxidative stress and a higher energetic metabolism. An increase in the content of muscle membrane phospholipids (sphingomyelin, phosphatidylserine, free sterols) was detected in the Seine vs. Douarnenez fish. The data integration allowed to hypothesize relationships between membrane phospholipids, xenobiotic metabolism, bioenergetics, and antioxidant defence. The genetic diversity considering neutral markers was maintained in the heavily polluted Seine population compared with the Douarnenez population. Finally, we suggest that the high physiological cost of tolerance to toxicants in the Seine flounder population could compromise its capacity to respond in the future to an additional stressor like warming waters in shallow depth. Thus, this population could be submitted to an ecological risk. [ABSTRACT FROM AUTHOR]

Recent years have brought the realization that evolutionary changes driven by selection can occur in ecological time scales. However, recent evolutionary events can be hard to detect and may easily go unnoticed. For harvested species, such cryptic diversity may lead to suboptimal management. These points are illustrated by the two flounder species in the Baltic Sea. Although early ecological studies identified two ecotypes of European flounder (Platichthys flesus) based on spawning differences, genomic studies only recently demonstrated that they were reproductively isolated species, P. flesus and P. solemdali , separated through rapid ecologically driven speciation. These morphologically indistinguishable species are harvested within a mixed-stock fishery. In the northern Baltic Sea flounder landings have declined since the mid-1980s, with a drop in the Gulf of Finland (GoF) being particularly dramatic (∼90%). Genetic analyses of historical otolith samples from GoF catches have revealed that back in 1983 the fishery unknowingly targeted primarily P. flesus , whereas thereafter almost exclusively P. solemdali. Hence, the case of two flounder species illustrates (i) how ecological studies stimulated genetic investigations leading to discovery of ecological speciation and (ii) how cryptic species turnover discovered with genetic tools in turn improved ecological understanding with benefits to management and conservation. [ABSTRACT FROM AUTHOR]

The European flounder Platichthys flesus (Linnaeus, 1758) displays two contrasting reproductive behaviors in the Baltic Sea: offshore spawning of pelagic eggs and coastal spawning of demersal eggs, a behavior observed exclusively in the Baltic Sea. Previous studies showed marked differences in behavioral, physiological, and life-history traits of flounders with pelagic and demersal eggs. Furthermore, a recent study demonstrated that flounders with pelagic and demersal eggs represent two reproductively isolated, parapatric species arising from two distinct colonization events from the same ancestral population. Using morphological data we first established that the syntypes on which the original description of P. flesus was based belong to the pelagic-spawning lineage. We then used a combination of morphological and physiological characters as well as genome-wide genetic data to describe flounders with demersal eggs as a new species: Platichthys solemdali sp. nov. The new species can be clearly distinguished from P. flesus based on egg morphology, egg and sperm physiology as well as via population genetic and phylogenetic analyses. While the two species do show some minor morphological differences in the number of anal and dorsal fin rays, no external morphological feature can be used to unambiguously identify individuals to species. Therefore, we developed a simple molecular diagnostic test able to unambiguously distinguish P. solemdali from P. flesus with a single PCR reaction, a tool that should be useful to fishery scientists and managers, as well as to ecologists studying these species.

The EU discard ban and its high-survival exemption exposed our lack of scientific evidence on discard survival in the fisheries. Discard survival is known to be highly variable and influenced by numerous factors, including conditions during the catch, on-board the fishing vessels, and post-discard. Therefore, obtaining unambiguous results in discard survival experiments is challenging. We conducted the first systematic year-round discard survival study of flatfish in the Western Baltic Sea on-board a commercial stern trawler under realistic fishing conditions (13 monthly hauls from May 2015 to May 2016) to test whether delayed mortality can be predicted by vitality scores and reflex action mortality predictor (RAMP) scores in combination with variable conditions during catch, processing, and post-release. The factors vessel type, gear, haul duration, fishing ground, depth, handling time, and processing procedures were kept constant as much as possible. On-board, live individual flatfish were tested for vitality and the presence of reflexes for RAMP, then "discarded" and kept in cages on the bottom of the seafloor for about a week after which the delayed mortality was determined. The proportions of "discarded" plaice, flounder, and dab that were dead after being kept in the cages ranged from 5% to 100%, 0% to 96%, and 33% to 100%, respectively. Higher mortalities occurred in summer-autumn when air and water temperatures were higher, catches smaller, and catches contained smaller proportions of roundfish. Relationships between RAMP scores and mortality probabilities varied substantially across the monthly trials. Indeed, in addition to RAMP or vitality scores and individual reflexes, the factors air and water temperature and catch weight and catch composition were significant in logistic GLMs explaining delayed mortality. Cross-validations indicated that delayed mortality could be predicted by these models with a reasonable accuracy. Nevertheless, the presence of possible confounding effects calls for caution in inferring causality and extrapolating the conclusions on predictability. [ABSTRACT FROM AUTHOR]

Sclerochronological studies based on hard structures of marine organisms are valuable tools—both for reconstructing past climate conditions and for predicting future impacts of environmental changes on marine resources. Existing archives, which house millions of fish otoliths (ear stones) constitute an excellent basis for such research; but, they remain underutilized. The objective of this project was to identify the factors that influence the annual growth patterns of the European flounder ( Platichthys flesus ) based on an analysis of otolith increments. We applied linear mixed models to develop a 74-year long chronology that reflects the inter-annual variations in flounder growth rates using otolith samples collected from 1957 to 2016 in the southern part of the Baltic Sea, which is considered to be highly vulnerable to global climate change. By analyzing the widths of otolith increments we revealed the existence of common environmental factors that influence fish growth. Using a mixed modeling framework, we incorporated a recent method to identify the optimal time window for climatic factors and showed that the most significant effect of the mean Baltic Sea Index occurs during August–December, while mean sea surface temperature is most significant from April–June. Change point analysis on the developed chronology identified major alterations occurred in flounder growth in 1988, 1992 and 2006. This result is in accord with published studies on regime shifts in the Baltic Sea ecosystem. This paper reports information concerning the response of the commercially important European flounder to the changing environment that may support future ecosystem-based management of fish stocks. Moreover, the results also highlight the potential for applying biochronological techniques to identify rapid regime shifts in marine ecosystems. [ABSTRACT FROM AUTHOR]

Standardized indices of abundance and size-based indicators are of extreme importance for monitoring fish population status. The main objectives of the current study were to (i) combine and standardize recently performed trawl survey with historical ones, (ii) explore and discuss the trends in abundance, and (iii) the trends in maximum length (Lmax) for cod (Gadus morhua) and flounder (Platichthys flesus) stocks in the Baltic Sea. Standardization of catch per unit of effort (CPUE) from trawl surveys from 1978 to 2014 to swept area per unit of time was conducted using information on trawling speed and horizontal opening of the trawls. CPUE data for cod and flounder stocks were modelled using generalized additive models (GAMs) in a delta modelling approach framework, while the Lmax data were modelled using ordinary GAMs. The CPUE time series of the Eastern Baltic cod stock closely resembles the spawning stock biomass trend from analytical stock assessment. The results obtained furnish evidence of the cod spill-over from Subdivisions (SD) 25–28 to SD 24. The decline of Lmax in recent years was evident for both species in all the stocks analysed indicating that the demersal fish community is becoming progressively dominated by small individuals. It is concluded that the standardization of long time series of fisheries-independent data constitutes a powerful tool that could help improve our knowledge on the dynamics of fished populations, thus promoting a long-term sustainable use of these marine resources. [ABSTRACT FROM AUTHOR]

Not available

Long-term monitoring data on the concentrations of biliary 1-hydroxypyrene (1-OHPyr) in flatfish, as a biomarker for polycyclic aromatic hydrocarbon (PAH) exposure, were analysed and evaluated to elucidate spatial differences and temporal trends in marine and estuarine PAH contamination in the Netherlands. Dab (Limanda limanda) and flounder (Platichthys flesus) with partly overlapping distributions were used as target species. In total 1831 bile samples were analysed individually: 417 dab in 1998-2005 and 1438 flounder in 1996-2012. The sampling procedure for flatfish and the PAH metabolites determination by means of high performance liquid chromatography (HPLC) with fluorescence (FL) detection were based on international guidelines. Measuring the absorbance at 380 nm was tested to correct for possible differences in feeding status, but this turned out not to be a suitable parameter for the standardisation of PAH metabolite concentrations. Both fish species showed statistically significant differences in biliary 1-OHPyr concentrations between various locations. The highest level of PAH contamination was found in flounder from the estuarine Western Scheldt, which might be partly due to local dredging activities. Dab from the central North Sea (Dogger Bank) showed the lowest level of PAH contamination. Analysis of all the data indicated mainly downward trends in PAH contamination, most clearly pronounced in the Dutch Wadden Sea. PAH exposure levels in the Dutch coastal waters including the Eastern Scheldt and the Wadden Sea, and also at the offshore North Sea monitoring sites represent levels of response that are not indicative of significant harm. In contrast, PAH contamination in the more industrialised Dutch estuaries (Western Scheldt and Ems Dollard) is still a cause for concern. Future monitoring should register the total bile volume, the sex of the fish and the method of fishing to improve the interpretation of the data. In addition, the biliary absorbance at 380 nm should be registered as it may help the interpretation of outliers in the data.

Background. The purpose of this study was to identify mathematical equations describing changes in a flatfish body shape along its longitudinal axis. The initial function for the description of a cross-section contour is the ellipse equation including a factor deforming the symmetry with respect to one of axes. Such equations may find their use in fisheries engineering and food-fish processing. Materials and methods. The morphometric examination of the fish raw material was carried out in order to check whether the proposed function meets expectations and draws a curve. The model fish species used was flounder, Platichthys flesus (L.). Results. The mathematical equation describing changes in a cross-section contour of flatfish body shape along its longitudinal axis. The high value of correlation coefficients (r > 0.99) showed that a hypothetical curve matches experiment results quite well. The equation describing the shape of a flatfish body cross-section contour can be defined by means of the ellipse equation including a factor deforming the symmetry with regard to one of its axes. The function represented by equation (8) draws a curve that follows the contour of the fish cross-section. Conclusion. The shape of flounder, defined in the presently reported study may have importance for sustainable and responsible fisheries, helping to design more selective fishing gear. It can also be used in food-fish engineering for designing more effective fish-processing machinery.

Trophic interactions play a key role in nursery habitats, and by affecting growth and condition of the juveniles, may control the quality of a given estuarine nursery. This study investigated the trophic ecology of flounder (Platichthys flesus) and common sole (Solea solea) juveniles in the Lima estuary nursery. Feeding location, main organic matter sources, and prey of the target species were assessed by carbon (δ13C) and nitrogen (δ15N) stable isotopes, as well as by stomach content analysis. The juveniles, macroinvertebrates, and sediment and water column samples were collected in August 2014 in the lower, middle and upper sections of the Lima estuary. The diet of 0+ flounder relied upon prey from the upper estuary (salinity >5), namely Chironomid larvae and Corophium spp. which showed the role of the upper estuary prey to the 0+ flounder diet and suggest the relative site fidelity of the young juveniles. In contrast, 1+ flounder juveniles had a diverse diet based on bivalves, polychaetes and crustaceans, and a variable stable isotope signature indicating they fed in different areas along the estuary. The 1+ sole juveniles also fed on polychaetes, crustaceans, and bivalves, but the stable isotope values suggested a dependence on the lower estuary (salinity >30) and marine food web sources. Such differential use of food may be understood as a strategic approach to reduce intra- and interspecific competition and thus ensuring the use of Lima estuary as nursery area for these two flatfish species.

Like many urban catchments, the River Thames in London is contaminated with plastics. This pollutant is recorded on the river banks, in the benthic environment and in the water column. The present study was conducted to assess the extent of microplastic ingestion in two River Thames fish species, the European flounder ( Platichthys flesus ) and European smelt ( Osmerus eperlanus ). Samples were collected from two sites in Kent, England; Erith and Isle of Grain/Sheppey, near Sheerness, with the latter being more estuarine. The results revealed that up to 75% of sampled European flounder had plastic fibres in the gut compared with only 20% of smelt. This difference may be related to their diverse feeding behaviours: European flounder are benthic feeders whilst European smelt are pelagic predators. The fibres were predominantly red or black polyamides and other fibres included acrylic, nylon, polyethylene and polyethylene terephthalate and there was no difference in occurrence between the sites sampled. [ABSTRACT FROM AUTHOR]

The article offers information about a study which aims to examine the bioenergetic transcriptomic responses of European flounder Platichthys flesus populations including the impacts of pollution and global warming.

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Abstract: Diablo (or SMAC) is a protein released from mitochondria following apoptotic stimuli and inhibits the actions of Inhibitors of Apoptosis (IAP) proteins. IAPs regulate the activity of caspases and NFkB, the primary executioners of apoptosis and of inflammation, respectively. Thus, Diablo is important for the regulation of cellular responses to damage. In Northern Europe, statutory governmental marine monitoring programs measure various biomarkers in flounder to indicate biological effects of pollutant exposure. More recently transcriptomic techniques have been applied in flounder to gain a more comprehensive understanding of pollutant effects, and to discover novel biomarkers. In most of these studies utilising flounder, Diablo was amongst the most highly increased transcripts identified. The aim of this study was to further examine piscine Diablo, at the gene level and mRNA level, after exposure to prototypical pollutants, and in flounder caught from polluted environments. The results show that two genes encoding Diablo exist in fish species, and in flounder one of these genes is increased in liver after exposure to polyaromatic hydrocarbons and polychlorinated biphenyls, and also in livers from fish living on contaminated estuarine sediments. Therefore, Diablo measurement has potential as a biomarker of pollutant exposure, and could indicate damaging effects of chemical contaminants. [Copyright &y& Elsevier]

The article presents the study which examined the predator-prey interactions in the intertidal systems. It particularly evaluates the temporal patterns in abundance and predation pressure by juvenile plaice and flounder on the Balgzand intertidal macrobenthos to determine the effects of predation by juvenile plaice and flounder in the Balgzand macrozoobenthic community. The data used in the study are the NIOZ fyke net programme and the NIOZ Balgzand high-water initiative, which were both taken from the western Dutch Wadden Sea.

The article discusses a study of migrations, site fidelity and homing ability of brand-marked flounder Platichthys flesus in the Tamar estuary, South West England from 1976 to 1980. An otter trawl or beam trawls were used to capture flounder and the freeze-branding technique was employed to mark the fish. Majority of female flounder caught at T2 and T9 stations toward the end of the spawning season were females. During the summer, five recaptures of marked flounder were from Plymouth Sound. Results show that the ability of the Tamar fish to home within the estuary and Plymouth Sound is better than their ability to locate their spawning grounds.

The occurrence of epizoic ciliates on the juvenile flounder, Platichthys flesus L., 1758, collected monthly by fishing net in Sinop's Sarıkum Lagoon Lake during the period from May 2003 to April 2004, was investigated. Five epizoic ciliate species, Trichodina jadranica (Raabe, 1958) Haider, 1964; Trichodina domerguei Wallengren, 1897; Riboscyphidia sp.; Ambiphrya sp.; and Vorticella sp., were found after examination of 296 juvenile flounder. Among these, T. jadranica was the dominant species. The prevalence and mean intensity values of the 5 epizoic ciliates were given as pooled data for 2 groups, namely mobiline ciliates and sessiline ciliates. Mobiline ciliates were commonly found on the gills of juvenile flounders, whereas sessiline ciliates were found only on fins. The highest prevalence and mean intensity levels of mobiline ciliates were recorded in the winter and spring seasons. Sessiline ciliates were absent in winter. The largest-sized juvenile flounder among the established 6 length classes had a higher intensity of mobiline ciliates. This study is the first on the epizoic ciliate fauna present on the juvenile flounder in Turkey. While T. jadranica is a new parasite record, the juvenile flounder is a new host record for T. domerguei in Turkey. [ABSTRACT FROM AUTHOR]

Abstract: Neoplasia and other histopathological lesions in flounder (Platichthys flesus) liver have been investigated in several European sea areas, including the Baltic Sea. Several studies have been able to link neoplasm epizootics in fish with the exposure to genotoxins such as polycyclic aromatic hydrocarbons (PAHs). The level of hydrophobic DNA adducts in tissue DNA reflects the exposure of the organism to PAHs. Using hydrophobic DNA adduct levels as biomarkers, possible PAH exposure was assessed in flounder from 10 different sites in the Baltic Sea, collected during the years 1995–1997. The results show that the overall levels of hepatic DNA adducts were low and, in general, the chromatograms appeared clean. The highest levels of DNA adducts were found at two sites in the southern Baltic Sea. There were no statistically significant differences in adduct levels between the sites. Our results indicate that flounder from studied off shore sites of the Baltic Sea had not been exposed to a greater extent to large polycyclic hydrophobic hydrocarbons in their environment. [Copyright &y& Elsevier]

Although the use of tributyltin in antifouling paints has been banned, this compound is still a serious pollutant of the marine environment. This paper describes a unique study in which European flounder (Platichthys flesus) were chronically (8 months) exposed to bis(tri-n-butyltin)oxide (TBTO) in the water under controlled laboratory conditions. Residue levels in selected tissues (liver, muscle) and general health status indices were measured and the effects on several organs (gills, liver, mesonephros, ovary/testis, spleen, and gastrointestinal tract) were examined histopathologically. Additionally, morphometric analysis of the thymus was performed. The major finding is that exposure of flounder to 5 μg TBTO/l over a period of 8 months, resulting in body burdens comparable to high field levels, induced significant reduction of thymus volume, possibly affecting immunocompetence of the animals. Chronic exposure of European flounder to tributyltin is therefore likely to affect the general health status of this species in heavily polluted aquatic environments. [Copyright &y& Elsevier]

Kijewska, A., Burzyński, A., and Wenne, R. 2009. Molecular identification of European flounder (Platichthys flesus) and its hybrids with European plaice (Pleuronectes platessa). – ICES Journal of Marine Science, 66: 902–906. European flounder (Platichthys flesus) and plaice (Pleuronectes platessa) are commercially important marine fish species inhabiting the continental shelf waters of Europe. Morphological similarity between the two makes it difficult to identify their hybrids, so species misclassification can generate errors in defining stocks in terms of their conservation and management. Flounder and plaice populations from the North Sea and the Baltic Sea were studied. Mitochondrial DNA (mtDNA) was used to confirm the morphological species identification. The set of molecular markers, two mitochondrial (cytochrome b and D-loop) and two nuclear (the ribosomal marker ITS and parathyroid hormone-related protein gene), was constructed to identify the two flatfish species and their hybrids. “Pure” flounder (P. flesus) were observed in the Bay of Gdańsk, Baltic Sea, and off the coast of Denmark in the North Sea. The fishing area near Bornholm in the Baltic is rich in P. flesus × P. platessa hybrids. The length difference of the amplified D-loop fragment was used for species identification. The characteristics of heteroplasmy in the control region (D-loop) can be useful as a population marker in the European flounder. Our studies demonstrate the utility of mtDNA polymorphism combined with nuclear molecular markers for correct identification of the morphologically similar and hybridized European flounder and plaice. [ABSTRACT FROM PUBLISHER]

We found significant population structure and isolation by distance among samples of flounder (Platichthys flesus) in the Baltic, Kattegat and Skagerrak seas using microsatellite genetic markers. This pattern was almost entirely due to a difference between flounder that have demersal spawning in the northern Baltic, as compared to pelagic spawners in the southern Baltic and on the west coast of Sweden. Among demersal spawners we found neither genetic differentiation nor any isolation by distance among sampling sites. We speculate that demersal flounder are descendants of a population that colonized the Baltic previous to pelagic spawners. The demersal flounder may thus have had longer time to adapt to the low salinity in the Baltic, and accordingly display egg characteristics that make it possible to reproduce at the low salinity levels in the northern Baltic. Among pelagic spawners significant isolation by distance was detected. Pelagic spawners have previously been shown to display clinal variation in egg size, which allows them to float also at the moderate salinity levels up to the region north of the island Bornholm. Management units for harvesting should ideally be based on true biological populations, and for the commercially important flounder up to 15 different management stocks in the Baltic have been suggested. We could not find a population genetic foundation for such a high number of management units, and our data suggest three management units: the northern Baltic (demersal populations), southern Baltic with the Öresund straits and the most northwestern sampling sites (Skagerrak, Kattegat and North Sea).Heredity (2008) 101, 27–38; doi:10.1038/hdy.2008.22; published online 7 May 2008 [ABSTRACT FROM AUTHOR]

Nakhlé, K., Cossa, D., Claisse, D., Beliaeff, B., and Simon, S. 2007. Cadmium and mercury in Seine Estuary flounders and mussels: the results of two decades of monitoring. – ICES Journal of Marine Science, 64: 929–938. The flounder (Platichthys flesus) is a flatfish that inhabits marine coastal environments, especially estuaries. It is an alternative quantitative biological indicator to the common marine mussel (Mytilus spp.), which is currently used as a sentinel species to monitor chemical contamination in numerous monitoring programmes. Findings from two decades of monitoring cadmium (Cd) and mercury (Hg) using both sentinel species in the Seine Estuary (France) are reported. For comparison, time-series of water concentrations for the same two metals at the mouth of the River Seine are given. Cd concentrations in the liver of the fish and in the soft tissue of mussels show similar temporal trends, consistent with the major temporal variations of Cd concentrations recorded in river water and with changes in industrial discharge of Cd (phosphogypsum waste) within the Seine Estuary. On the other hand, Hg concentrations in the muscles of flounders show temporal variations with no link to that observed in mussels or fluvial Hg contributions, which are in fact nearly covariant. It is concluded that optimization of the use of flounders as sentinel organisms for monitoring temporal trends of metal contamination in estuarine environments requires in-depth knowledge of its ecology within the area studied. An adapted sampling strategy based on this knowledge should provide results that are easier to interpret. [ABSTRACT FROM AUTHOR]

Tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) are widely used flame retardants that have increasingly been found as contaminants in the aquatic environment. In the present study, European flounder (Platichthys flesus) were chronically exposed to TBBPA; (105 days) and HBCD (78 days), in a wide range including environmentally relevant concentrations. TBBPA was administered via the water, whereas HBCD was administered in food and sediment, or in sediment alone. Chemical analysis of muscle showed an average increase in internal concentrations of approximately two orders of magnitude for both compounds tested. Animals exposed to HBCD via sediment alone (8000μg/g total organic carbon, TOC) showed a proportional increase of α-HBCD in muscle compared to animals exposed via food and sediment. In both studies, exposure to the test compounds did not affect general health and toxicity parameters (behavior, survival, growth rate, relative liver and gonad weight). Hepatic microsomal enzyme activities (TBBPA: EROD; HBCD: EROD, PROD, and BROD) were not induced by any of the tested chemicals. Aromatase activity in male gonads showed a mild increase with rising TBBPA levels. There were no morphological and immunohistochemical indications for increased production of the yolk precursor protein vitellogenin (VTG) in animals exposed to TBBPA and HBCD; immunochemical analysis of plasma VTG levels showed no dose response in animals exposed to TBBPA. In animals exposed to TBBPA, levels of the thyroid hormone thyroxin (T4) increased with internal concentrations of the test compound, possibly indicating competition of TBBPA for plasma protein binding. Triiodothyronin (T3) levels were not affected and histology showed no signs of altered thyroid gland activity. Other organs investigated (liver, gills, kidney, skin, and gonads) revealed no histological changes related to TBBPA or HBCD exposure. Overall, the present results indicate limited endocrine effects of these widely used flame retardants in a test species representative of European estuaries at environmentally relevant exposure levels and at internal levels up to 4300ng TBBPA/g wet weight, and 446μg HBCD/g lipid weight in flounder muscle. [Copyright &y& Elsevier]

Abstract: The aim of the present study was to examine the activity of hepatic glutathione S-transferase (GST) in flounder, Platichthys flesus, as a potential biomarker of exposure to xenobiotics present in the environment. The fish were collected along known pollution gradients and from areas regarded relatively free of anthropogenic input. GST was measured spectrophotometrically in each sampled specimen of flounder. The databases from the studies performed by two research institutes were compiled, and generalized linear models were used to analyze the dependence of the enzyme activity on the time and area of sampling and on selected biological parameters of the fish. Fish sex, sampling area, year, month, water temperature, and somatic indices (gonado-somatic index, hepato-somatic index) were significant in the model of GST activity. The three annual datasets showed that the biomarker activities exhibited in the Gulf of Gdansk were significantly different from those measured in the areas off the coast. [Copyright &y& Elsevier]

This study examined the electrical firing activity of neuroendocrine Dahlgren cells in the caudal neurosecretory system (CNSS) of the euryhaline flounder in vivo. Intracellular recordings revealed generally similar activity patterns and membrane properties to those previously reported in vitro. To investigate the potential role of the CNSS in osmoregulatory adaptation, extracellular, multiunit, recordings compared the activity patterns of Dahlgren cells in fully seawater- and freshwater-adapted fish. The proportion of cells showing bursting (as opposed to phasic or tonic) activity was greater in seawater- than in freshwater-adapted fish, as was the Correlation Index, a measure of the degree of correlation between firing activities of cells recorded simultaneously from the same preparation. Acute transfer of fish from seawater to freshwater gill perfusion led to recruitment of previously silent Dahigren cells and a reduction in Correlation Index; freshwater to seawater transfer increased the Correlation Index. Severing the spinal cord anterior to the CNSS led to an increase in overall Dahlgren cell activity. Electrical stimulation of branchial nerve branches providing input to the brainstem, or tactile (pinch) stimulation of lips or fins, led to a reduction in CNSS activity lasting up to 500 s, indicating the presence of descending modulatory pathways from the brain. These results are consistent with a role for CNSS neuropeptides, urotensins, in supporting survival in a hypertonic, seawater, environment. [ABSTRACT FROM AUTHOR]

Abstract: Physiological and genetic responses of flounder Platichthys flesus populations were investigated along the French Atlantic Coast in one moderately contaminated estuary (Ster) and three contaminated estuaries (Seine, Loire and Gironde). The focus of this study was to explore the relationship between stress resistance and energetic trade-offs, in order to detect possible differential physiological capacities or performances between individuals carrying particular alleles or genotypes (allozyme data) characterised as “tolerant” or “sensitive”. A general reduction of the relative fecundity, the growth rate and the condition factor was highlighted in contaminated fish populations, suggesting that survival in such polluted systems implies energetic costs for fish thus reducing the energy available for particular functions. A lower observed heterozygosity was also detected in contaminated populations with respect to the Ster, suggesting a general decrease in genetic variability in response to chemical stress (with an exception for the Seine estuary). This study confirmed the previously detected relationship between PGM 85, AAT1 95 alleles and reduced DNA damage in contaminated fish [Marchand, J., Tanguy, A., Laroche, J., Quiniou, L., Moraga, D., 2003. Responses of European flounder Platichthys flesus populations to contamination in different estuaries along the Atlantic coast of France. Mar. Ecol. Prog. Ser. 260, 273–284] and furthermore suggested that, reduced fecundity and condition factor associated to the individuals carrying the previous alleles, were also reflecting the cost of resistance to stress in polluted populations. The cost of tolerance to stress as well as the high gene flow from neighbouring populations less exposed to contamination may explain the apparently moderate increase of the suspected “tolerant” alleles in contaminated flounder populations. [Copyright &y& Elsevier]

The hepatic detoxification system in Baltic flounder and rainbow trout was characterized under experimental conditions. Fish were exposed to benzo[a]pyrene (BaP, 10 and 50 mg/kg, ip) or vehicle for 2, 5, and 10 days (in rainbow trout also for 20 days) and then sacrificed. Control fish were sampled at Days 0 and 10 (flounder) or Day 20 (rainbow trout). The hepatic distribution of CYP1A was analyzed immunohistochemically and microsomal ethoxyresorufin O-deethylase activity was determined spectrophotometrically. The kinetics of the CYP1A responses (EROD) was similar in both species, while a species-specific difference in the magnitude of the response was observed. CYP1A was demonstrated in the hepatocytes in both fish species 2 days after BaP administration and throughout the experiment. In rainbow trout a CYP1A response in the vascular endothelium of liver parenchyma was detected 2 days postadministration, while the corresponding reaction in flounder was seen 5 days postadministration. Thus, our results confirm previous reports that the CYP1A response is species specific. Furthermore, the induction of hepatic CYP1A in Baltic flounder reflects pathophysiological effects induced by polycyclic aromatic hydrocarbon compounds and, consequently, is a parameter useful when monitoring the anthropogenic effects on the Baltic Sea environment. [Copyright &y& Elsevier]

The estrogenic effect of dietary 4-tert-octylphenol in the flounder Platichthys flesus was investigated in the laboratory. In the first experiment male flounders were fed doses of 10, 50 and 100 mg 4-tert-octylphenol kg−1 BW or 0.05 mg 17β-estradiol kg−1 BW every second day for 10 days. Increases in the plasma content of vitellogenin were observed on day 6 by the first sampling in all treated groups. An effect of octylphenol on the size of the liver and testis was only seen in one of the exposed group (50 mg 4-tert-octylphenol kg−1 BW). An increase in the concentration of 4-tert-octylphenol was found in both liver and muscle tissues of all 4-tert-octylphenol treated fish. The concentration of 4-tert-octylphenol (ng g−1 WW) in liver tissue was four to five times greater than the concentration in muscle tissue. Only about 8% of the 4-tert-octylphenol administered to the group receiving 50 mg 4-tert-octylphenol kg−1 BW was retained in the liver and the muscles at the end of the experiment. In the second experiment male flounders were exposed to a low dose range of 4-tert-octylphenol (1 to 25 mg 4-tert-octylphenol kg−1 BW) in order to establish the dose-response relationship of 4-tert-octylphenol when applied by feeding to flounder. Vitellogenin induction (LOED) occurred at 10 and 5 mg 4-tert-octylphenol kg−1 BW after, respectively, 6 and 11 days of exposure. Based on a logistic regression analysis the effect dose (ED50) could be determined as 8.2 and 5.6 mg 4-tert-octylphenol kg−1 BW on day 6 and 11, respectively. 4-tert-octylphenol accumulated in liver, muscle and testis tissue, and a significant accumulation in liver was found at 2.5 mg 4-tert-octylphenol kg−1 BW and in muscle and testis at 5 mg 4-tert-octylphenol kg−1 BW. Finally, a positive correlation between the plasma vitellogenin concentration and the liver tissue concentration of 4-tert-octylphenol was established as well as a positive correlation between the content of 4-tert-octylphenol in liver and muscle/testis tissue. [Copyright &y& Elsevier]

This study investigated the response of biomarker measurements and histopathological indicators of polycyclic aromatic hydrocarbon (PAH) exposure in the flounder (Platichthys flesus L.). Flounder were fed food spiked with a mixture of four PAHs at an environmentally relevant range of concentrations for either one or six months. Ethoxyresorufin-O-deethylase (EROD) activity was elevated following 1 month exposure to PAH concentrations up to 50 mg kg−1 in food. Bile metabolite concentrations were found to increase with PAH concentration, up to 500 mg kg−1 PAH. By comparison, no DNA adducts were detected and there were no significant histopathological changes observed. After 6 months exposure, EROD levels were not elevated but bile metabolites showed a similar dose dependent relationship as in the 1 month experiment, while DNA adducts were only detected in the highest PAH exposure groups. No significant histopathological changes were observed. The results are discussed with respect to the implications for the use of these methods in environmental monitoring studies. [Copyright &y& Elsevier]

Screening of a flounder ovary cDNA library with a rainbow trout p53 probe led to the isolation of a p53-unrelated cDNA encoding an unknown 161 amino acid protein. In view of its apparent molecular weight and yet unknown function, the deduced protein was named Xp18. Corresponding orthologous cDNAs or expressed sequence tags have been identified in several species including human, rodents, bovine, chicken and zebrafish and a related cDNA has also been isolated in the fruit fly. Deduced amino acid sequences appeared to be extremely well conserved throughout vertebrate evolution. Structure predictions suggested that Xp18 may correspond to an integral protein comprising four transmembrane domains. The charged C-termini of all known vertebrate Xp18-like proteins displayed a characteristic KXKXX motif which is considered as an endoplasmic reticulum targeting sequence. Gene expression, as shown by Northern blot and quantitative reverse transcription-polymerase chain reaction analysis, was significantly higher in the ovary and to a lesser extent in the brain. Xp18 transcripts were also detected by in situ hybridization in most of the circumventricular regions of the brain of adult flounders. The gene encoding the human protein is located on chromosome Xq22.1, a genome region involved in numerous genetic diseases including premature ovarian failure. [Copyright &y& Elsevier]

In connection with the BMB/ICES Sea-going Workshop “Fish Diseases and Parasites in the Baltic Sea”, 200 specimens of flounder Platichthys flesus from eight stations (25 from each) distributed from the southwestern (Mecklenburg Bight) to the northeastern Baltic Sea (Gulf of Finland) were examined for metazoan parasites. A few species (e.g. Hysterothylacium aduncum, Cucullanus heterochrous, Cucullanellus minutus, and Pomphorhynchus laevis) were found at virtually all stations. Typical “marine” species (Podocotyle atomon, Brachyphallus crenatus, Anisakis simplex, Holobomolochus confusus, and Lernaeocera branchialis) were found at the western stations only, whereas the metacercariae of Diplostomum spathaceum, and Cotylurus sp., immature Corynosoma sp., the larvae of Raphidascaris acus and Contracaecum osculatum were most common towards the east and north. Echinorhynchus gadi only occurred at the western and southern stations. The small encapsulated larvae of the bird nematodes Contracaecum sp., Paracuaria sp., and Cosmocephalus sp. were found at most stations. The effects of salinity on the patterns observed in relation to the distribution of intermediate and final hosts are discussed. [ABSTRACT FROM PUBLISHER]

Ulcerated fish of six different species were collected during the BMB/ICES Sea-going Workshop “Fish Diseases and Parasites in the Baltic Sea”, 25 November to 8 December 1994, and examined for bacteriological infections. Atypical Aeromonas salmonicida strains were isolated from the majority of the ulcers of dab Limanda limanda, flounder Platichthys flesus, and turbot Scophthalmus maximus. A fast-growing strain was isolated in pure cultures from both ulcers and visceral organs of viviparous blenny Zoarces viviparus. Available data suggest that atypical A. salmonicida is generally involved in the development of ulceration’s in Baltic flounder and probably also in other fish species. The strains isolated from ulcerated flounders were indistinguishable from those previously reported from this species from the Baltic Sea and the North Sea, and the ulcer disease is considered to be associated with one, well-defined biotype of A. salmonicida. [ABSTRACT FROM PUBLISHER]