European Flounder Platichthys Flesus Research Articles

Spatial and temporal patterns of gonadal maturation and spawning in European flounder Platichthys flesus at its southern continental edge

The European flounder (Platichthys flesus) is a marine flatfish with high plasticity in several life-history traits, including spawning sites and habitat use patterns. With the overarching goal of understanding the use of estuaries in connection with maturation and reproduction in adult flounder, this study investigates its reproductive cycle in the Douro Estuary (NW Portugal), at the southern edge of its geographical distribution. Adults were caught by monthly trawling from November 2016 to November 2017. Sex ratio and length-weight relationships were determined. The annual reproductive cycle was described using a combination of gonadosomatic (GSI), hepatosomatic (HSI), and general fish condition (Kn) indices, seasonal gonad development staging (macroscopic and histological), and quantification of plasma sexual steroids. Total sex ratio was 1 M:3 F, and females presented negative allometric growth, while males’ growth was isometric. The various indices consistently indicated that the greatest reproductive activity occurred between January and March, peaking in February. However, some females at advanced reproductive stages (late vitellogenesis), high GSI values and steroid hormone (E2) levels were observed as late as May. Females in spawning condition, i.e., undergoing full oocyte maturation and ovulation, were never found, unlike males who exhibited spermiation within the estuary. Sexual differences in migration patterns were also suggested: males seem to leave earlier and stay longer in offshore spawning grounds, while females return to the estuary shortly after spawning. Overall, there was a good correlation between GSI, seasonal hormone cycling, and sexual maturity of female and male flounder, supporting the use of circulating sex steroids as a less invasive tool to assess maturity status.

Haracteristic of the biology of the European flounder Platichthys flesus (Pleuronectidae) of the lower reaches of the Mezen river according to research data 2010–2016

The biological characteristics of the European flounder of the lower reaches of the Mezen River are described. The maximum age of 18 years was noted, the maximum zoological length and weight: 41,2 cm and 680 g. The size and weight characteristics of individuals for each age are given. The relationship between the length and mass of the river body is described by a power function. Single maturing individuals were caught at the age of 4 years in females and 3 years in males. The bulk of the fish ripens at 4–5 years of age. Food items are marked: amphipods, bivalve mollusks, insect larvae, including brooks, sipunculids, fish objects. The average absolute fecundity of European flounder is 550 thousand eggs.

Видовой состав рыб губы Белокаменная (Кольский залив) в мае и августе–октябре 2022 года

The species composition of the ichthyofauna of Belokamennaya Bay were carried out from May to October 2022 was studied. 10 species of fish belonging to 6 families were found in the study area. Most of the species belong to the boreal complex. The commercial status in the Barents Sea has seven (70 %) species of fish. The European flounder Platichthys flesus (Linnaeus, 1758) dominated in abundance (35 %) and the pollock Pollachius virens (Linnaeus, 1758) (33 %). In terms of biomass, a large share of the catch (43.6 %) was occupied by European flounder, and the European sculpin Myoxocephalus scorpius (Linnaeus, 1758) also accounted for a significant part – 22.2 %.

Promoting the use of non-lethal sample collection for analysing the trophic relationships of inshore flatfish populations using stable isotope analysis

Trophic studies on inshore flatfish populations usually rely on stomach content analyses and/or stable isotope analysis (SIA) of dorsal white muscle that involves the collection of samples from euthanised fishes. To promote the use of non-lethal sampling methods in inshore flatfish populations of relatively high intrinsic angling and/or ecological value, the applicability of using fin tissue and/or epidermal mucus as non-lethal alternatives to muscle in SIA studies was assessed for European flounder Platichthys flesus, plaice Pleuronectes platessa and common sole Solea solea. In all species, the results indicated that there were significant differences in the δ13C and δ15N values of dorsal muscle versus their fin and mucus samples. These significant differences were, however, predictable by linear regression, with regression coefficients produced for converting fin and mucus SI values to the equivalent muscle SI values. The use of combined data across the species also provided regression coefficients for converting fin and mucus SI to equivalent muscle values for flatfish populations more generally. These results indicated that there are tissue alternatives to dorsal muscle that can be applied to the SIA of flatfish populations, with these tissues able to be collected using non-lethal sampling methods.

Frequencies of lateral morphs in different age classes of the flounder Platichthys flesus (Pleuronectidae) from the White Sea

In the populations of the European flounder Platichthys flesus (Linnaeus, 1758), the proportions of left- and right-sided individuals vary widely, and possible causes of this variation remain little explored. The hypothesis of ecological segregation of phenotypical morphs in the European flounder relies primarily on observations of certain differences in morphology and foraging performance between the left- and right-sided individuals. The flounders of different sex and size/age, however, can differ in the character of biotic associations with the environment and other hydrobionts. We have examined the interaction of size/age and sex of the fish with the probability of encountering left-sided individuals in 4 populations of the European flounder from the White Sea basin. The results of the study have shown that the proportion of the reversed individuals did not differ among the flounders of various size and age in all the populations studied. The proportion of the left- and right-sided morphs in different size-age classes in all investigated populations did not depend on the sex of the fish. Revealed interpopulation diversity of phenotypic composition of flounder from the White Sea is not connected with the size/age and sex structure of compared samples.

Spatial Variation in the Frequency of Left-Sided Morph in European Flounder Platichthys flesus (Linnaeus, 1758) from the Marginal Arctic (the White Sea)

The European flounder, Platichthys flesus, is a polymorphic flatfish, which has a large population variation in the proportion of left-sided and right-sided morphs across its geographic range. We compared the frequencies of these morphs in the White Sea (Kandalaksha, Onega, Dvina, and Mezen bays), the region in the northeastern part of species’ range adjacent to the Arctic. The proportion of the two morphs in the populations of White Sea flounders showed high variability and specific regional characteristics. The highest frequency of left-sided individuals was observed in the northwestern (Kandalaksha Bay) and southwestern (Onega Bay) parts of the White Sea. Flounders living in the eastern part of the White Sea (Dvina and Mezen bays) showed a much lower frequency of this trait. No consistent pattern of geographic variation in the proportion of the morphs was found in the geographic range of P. flesus. The lowest frequencies of left-sided individuals were recorded in the flounder populations living at the eastern and western margins of the geographic range. Geographic variation in the proportion of left-sided individuals in flounder populations is likely to be determined by a set of biotic and abiotic factors. Selective influence of the latter, acting through the trophic relationships of this species with other marine organisms, can differ in different parts of flounder’s geographic range.

Long-term dynamics of the proportion of left-sided individuals in the populations of the European flounder Platichthys flesus (Linnaeus, 1758) in the White Sea

Interannual variation in proportion of left-sided individuals has been studied in the populations of the European flounder from Onega (2002–2019), Mezen (2010–2016), and Dvina (2005–2019) bays of the White Sea. It was found that the flounder populations show no statistically significant and consistent changes in this character. The frequency of left-sided individuals in the local populations and the character of interpopulation differences in different years of the observation period remain relatively constant. The comparison of the results of this study with those of earlier studies reveals a similarity in proportions of left-sided fish over the past 40–60 years in flounder populations of the Kandalaksha Bay and Onega Bay. These results highlight the importance of the proportion of left-sided morphs for the analysis of population differentiation of the European flounder in the White Sea.

Development in the European flounder (Platichthys flesus) of a q-PCR assay for the measurement of telomere length, a potential biomarker of pollutant effects for biomonitoring studies

Telomeres protect the coding sequence of chromosome ends and Telomere Length (TL) has been proposed as a biomarker of cellular aging, cumulative stress exposure and life-span in humans. With the aim to propose new biomarkers, a q-PCR protocol was adapted for the measurement of TL in the European flounder Platichthys flesus. The protocol was then applied in 2-year-old flounders from the Seine Estuary.The absolute TL in the flounder is 54 ± 13 kbp per genome (mean ± standard error). Considering relative or absolute TL, no correlation was observed with DNA damage and any of the measured contaminant concentrations (trace elements, metabolites of polycyclic aromatic hydrocarbons, polychlorobiphenyls, organochlorinated pesticides, polybrominated diphenyl ethers, perfluoroalkyl substances). Because sampling was limited, further investigations are required to state a possible impact of chemical pollution on flatfish telomeres. This is motivated by correlations observed with organochlorinated compounds when decreasing statistical significance (p ≤ 0.10).

A de novo Transcriptome Assembly of the European Flounder (Platichthys flesus): The Preselection of Transcripts Encoding Active Forms of Enzymes

The RNA sequencing data sets available for different fish species show a potentially high variety of forms of enzymes just in teleosts. This is primarily considered an effect of the first round of whole-genome duplication with mutations in duplicated genes (isozymes) and alternative splicing of mRNA (isoforms). However, the abundance of the mRNA transcript variants is not necessarily reflected in the abundance of active forms of proteins. We have investigated the transcriptional profiles of two enzymes, aralkylamine N-acetyltransferase (AANAT: EC 2.3.1.87) and N-acetylserotonin O-methyltransferase (ASMT: EC 2.1.1.4), in the eyeball, brain, intestines, spleen, heart, liver, head kidney, gonads, and skin of the European flounder (Platichthys flesus). High-throughput next-generation sequencing technology NovaSeq6000 was used to generate 500M sequencing reads. These were then assembled and filtered producing 75k reliable contigs. Gene ontology (GO) terms were assigned to the majority of annotated contigs/unigenes based on the results of PFAM, PANTHER, UniProt, and InterPro protein database searches. BUSCOs statistics for metazoa, vertebrata, and actinopterygii databases showed that the reported transcriptome represents a high level of completeness. In this article, we show how to preselect transcripts encoding the active enzymes (isozymes or isoforms), using AANAT and ASMT in the European flounder as the examples. The data can be used as a tool to design the experiments as well as a basis for discussion of diversity of enzyme forms and their physiological relevance in teleosts.

Feeding strategies and body condition of juvenile European flounder Platichthys flesus in a nursery habitat

AbstractEstuarine habitats are major nurseries for the European flounder Platichthys flesus, with different year classes sharing food and space resources. Hence, an understanding of feeding strategies that optimize resource use and maintain carrying capacity is fundamental for sustainable and successful ecosystem management. The main feeding areas of juvenile European flounder (including 0-group and 1-group age classes) in the Lima estuary (northern Portugal) nursery ground were investigated by integrating stomach content analyses with stable isotopic values (δ13C and δ15N) and fish condition indices (Fulton K and RNA:DNA ratio). The 0-group flounder that were associated with the upstream section of the estuary presented the lowest δ13C value (−25.58 ± 1.86‰), while 1-group flounder exhibited a higher δ13C value (−22.59 ± 2.51‰), indicating use of the more saline areas of the estuary (lower and middle sections). The two age groups did not differ in terms of δ15N (0-group: 13.93 ± 0.29‰; 1-group: 13.50 ± 0.96‰), indicating similar trophic levels. The low salinity upper estuary was the main feeding area of 0-group flounder (74%), while 1-group flounder fed along the estuary both upstream (52%) and downstream (48%). Juvenile flounder showed high individual condition based on the Fulton K index (0-group: 1.05 ± 0.08; 1-group: 1.07 ± 0.05) and RNA:DNA (0-group: 1.70 ± 0.70; 1-group: 1.41 ± 0.47). These indices deal with fish health, and hence indicate nursery habitat quality. It is concluded that in this temperate nursery habitat, different feeding strategies sustained the condition of the European flounder juveniles, compared with other flounder populations.

Indicators of Osmotic and Ion Regulation in the Fish of the White Sea

The osmotic concentration; the concentrations of sodium and potassium; the content of total, free, attached water fractions in plasma; and the content of interstitial and cerebrospinal fluid, in the brain, muscles, liver, and erythrocytes typical for the fish in the native environment were determined for cod Gadus morhua. Under stress, a protective reaction is implemented, it prevents tissue dehydration by increasing the osmotic concentration in the interstitial fluid in the European flounder Platichthys flesus, spotted wolffish Anarhichas minor, lumpsucker Cyclopterus lumpus, and short-horn sculpin Myoxocephalus scorpius. The osmotic concentration preconditioned by inorganic ions in the muscles, liver, and erythrocytes of cod is significantly lower compared to the internal environment. The lack of ions in the tissues is compensated by the accumulation of organic osmolytes. Similar patterns are observed in euryhaline species when acclimated to the marine environment and in freshwater fish in the zone of critical salinity. Values of the osmotic concentration and sodium and potassium content in the blood plasma and tissues of the White Sea fish refer to the corresponding regulation ranges obtained for euryhaline and freshwater fish in the salinity range compatible with life activity.

Seasonal Dynamics of Biological Indicators of the European Flounder Platichthys flesus Linnaeus, 1758 in the Central Part of the Kola Bay in 2018

The data on the seasonal dynamics of biological indicators of European flounder are presented for the central part of the Kola Bay for the year of 2018. In particular, the size-age and population sexual structure, feeding, and distribution density of European flounder were considered. The constants of the power equation of the dependence of the fish body weight on its length were obtained, the peculiarities of the fish growth were revealed. It is assumed that European flounder is one of the important components of the coastal ecosystems of the Kola Bay.

First record of niche overlap of native European plaice (Pleuronectes platessa) and non-indigenous European flounder (Platichthys flesus) on nursery grounds in Iceland

First record of niche overlap of native European plaice (Pleuronectes platessa) and non-indigenous European flounder (Platichthys flesus) on nursery grounds in Iceland

Variability of squamation of European flounder Platichthys flesus (Pleuronectidae) in the White Sea

Squamation of the European flounder Platichthys flesus is formed by the common cycloid scales and the bony plates. The number of the bony plates and their localization on the body vary considerably in the flounders from different parts of their range. Study of the variability of bony plates coverage in the European flounder are of importance for understanding structural diversity and for use of this character for morphological differentiation of the local populations. We compared the bony plates on the eye side of the body in the flounders from Chupa Inlet (Kandalaksha Bay) and from the delta of the North Dvina River (Dvina Bay). The localization and the number of the bony plates near the bases of dorsal, anal, pectoral fins and above/below of the lateral line were analyzed. Our results clearly showed that the compared samples can be characterized by certain phenotypes, differing by number and location of the bony plates on the eye side of the fish body. The individuals of one phenotype were found in Chupa Inlet only. Small amount of the bony plates on the body and the presence of relatively wide aggregation of the bony plates near the pectoral fin are the traits of this phenotype. Three phenotypes were distinguished among fishes from the North Dvina delta. The absence of the bone plates on the most part of the body is typical for the prevalent phenotype. Individuals of the second phenotype were similar to the flounder from Chupa Inlet. Large amount of the bony plates covering the whole eye side of the body is characteristic for the third phenotype. The obtained results complement the existing data on the variability of squamation of the White Sea flounders, and indicate the importance of this character in the study of the differences between local populations in this region.

Age and growth of European flounder from the Chupa Inlet (Kandalaksha Bay, the White Sea)

We studied age structure, growth and distribution of European flounder Platichthys flesus at the sea in Chupa Inlet (Kandalaksha Bay, the White Sea). Immature and mature fishes fed at shallows of Chupa Inlet and adjacent open sea area in June-August. Size-age and sex composition of fishes in catches are presented in the paper. Individuals of 17–27 cm length and 4–5 year age constituted the majority of catches (45%). On the whole, males numerically predominated over females in the samples. Analysis of sexual differences of growth has shown that females grew faster than males. The most intensive growth took place in July–August, according to the increments on the otoliths. Growth rate of the flounder from Chupa Inlet appeared to be similar to the growth rate of the flounder from other open shore sites of Kandalaksha Bay. We have compared also peculiarities of growth and age structure of flounder populations from Kandalaksha Bay to those from other bays of the White Sea. Significant differences of the growth rate were found between flounders from Kandalaksha, Onega, Dvina and Mezen' Bays. Both males and females from Onega Bay grew faster than other. Growth rate of fish decreased towards the north (Kandalaksha Bay) and the north-east (Mezen' Bay). The most slow-growing flounder inhabited shallows of Mezen' Bay. Statistical analysis has shown that age structure of flounder populations varied in different bays of the White Sea, and observed regional variations were characteristic for both males and females. Flounder population in Onega Bay was characterized by the dominance of the younger individuals compared to populations in other bays. The greatest mean age of flounder was registered in populations from the north-west (Kandalaksha Bay) and the north-east (Mezen' Bay) parts of the White Sea. Males and females in populations from Onega and Dvina Bays differed significantly in the mean age, and as a rule females were older. No age differences between sexes were found in flounder population of Mezen' Bay. We suppose that temperature conditions were among the main factors influencing regional differences in growth rate and age structure of the flounder populations in the White Sea.

Reconciling differences in natural tags to infer demographic and genetic connectivity in marine fish populations

Processes regulating population connectivity are complex, ranging from extrinsic environmental factors to intrinsic individual based features, and are a major force shaping the persistence of fish species and population responses to harvesting and environmental change. Here we developed an integrated assessment of demographic and genetic connectivity of European flounder Platichthys flesus in the northeast Atlantic (from the Norwegian to the Portuguese coast) and Baltic Sea. Specifically, we used a Bayesian infinite mixture model to infer the most likely number of natal sources of individuals based on otolith near core chemical composition. Simultaneously, we characterised genetic connectivity via microsatellite DNA markers, and evaluated how the combined use of natural tags informed individual movement and long-term population exchange rates. Individual markers provided different insights on movement, with otolith chemistry delineating Norwegian and Baltic Sea sources, whilst genetic markers showed a latitudinal pattern which distinguished southern peripheral populations along the Iberian coast. Overall, the integrated use of natural tags resulted in outcomes that were not readily anticipated by individual movement or gene flow markers alone. Our ecological and evolutionary approach provided a synergistic view on connectivity, which will be paramount to align biological and management units and safeguard species’ biocomplexity.

Assessing the effects of internal and external acoustic tagging methods on European flounder Platichthys flesus

Fish telemetry studies give unique information about fish movements (migrations), but there are still several methodological constraints. A critical step is the choice of an appropriate tag and tagging method, essential to guaranteeing that the tagged fish is representative of the general wild population. The effects of two tagging methods with acoustic transmitters on the behavior, survival, condition, and growth of the European flounder Platichthys flesus (L.) were evaluated in tank experiments. Two 33-day assays were conducted: one with adult flounder to test intracoelomic (internal) and external tagging with Vemco V7-2 L dummy tags, and a second assay with juveniles using only external tags. Intracoelomic implantation resulted in very low survival rate (10%), fish lethargy, and a lack of response to food. External tagging did not affect behavior but had negative effects on the final condition of adult flounder, and on the specific growth rates (SGR) of smaller-sized fish. The external tagging method is the most appropriate for P. flesus because of the technique’s simplicity, expedience, and fewer negative effects upon the fish.

High incidence of otolith abnormality in juvenile European flounder Platichthys flesus from a tidal freshwater area

ABSTRACTOtolith abnormality has been reported for a wide range of freshwater and marine fish species. In this study, the sagittal otolith morphology and mineralogy of juvenile European flounder, Platichthys flesus, were examined to describe the incidence and types of structural deformities in this species. Juvenile flounder were collected over the years 2013–2015 in the tidal freshwater section of an estuarine nursery (Minho estuary, NW Portugal). Otolith abnormality was found in 43% of the individuals and, in most cases, occurred in both otoliths. Despite an abnormal mineralogy confirmed by scanning electron microscopy, the morphometry and the mineral polymorph composition of abnormal otoliths did not differ from normal ones (i.e. aragonite). This contrasts with other studies where vaterite and/or calcite were found to replace aragonite in abnormal otoliths. Further studies are needed to elucidate whether abrupt salinity changes associated with habitat transitions may have played a role in the abnormal otolith biomineralization in this species.

Contrasting patterns of energy metabolism in northern vs southern peripheral European flounder populations exposed to temperature rising and hypoxia

A two months common garden experiment was carried out to explore the potential differences of energy metabolism in northern core (France, 50°N and 47°N) vs southern peripheral (Portugal, 41°N) populations of European flounder Platichthys flesus, submitted to cold condition (CC: water temperature = 10 °C) and to warm and hypoxic condition (WHC: water temperature = 22 °C, and moderate hypoxia with O2 saturation = 40% during the last 6 days). Convergent growth rates (in length) were observed in the different populations and conditions, when the southern peripheral population of Portugal did not grow under cold conditions. A general reduction in liver lipid storage was observed in all populations subjected to WHC when compared to CC, whereas muscle lipid storage was unaffected. The thermal and hypoxia treatment induced changes in muscle phospholipids (PL) ratios: phosphatidylserine/PL, phosphatidylinositol/PL, between northern and southern populations. Fish from northern estuaries displayed marked anaerobiosis in WHC (increased liver LDH activity) vs marked aerobiosis under CC (higher muscle CS and CCO activities). Contrariwise, fish from the southern estuary displayed equilibrium between anaerobiosis and aerobiosis activities in WHC. Flounders from the southern population exhibited generally lower G6PDH activity (proxy for anabolism and for defense against oxidative damage), tissue-specific anaerobiosis response (muscle LDH activity) and lower CS and CCO muscle activities (aerobiosis markers) when compared to northern populations. Globally, these inter-population differences in bioenergetics suggest that southern peripheral vs northern core populations have developed differential capacity to cope with interacting stressors and that much of this variation is more likely due to local adaptation.

Impact of salt-marsh management on fish nursery function in the bay of Aiguillon (French Atlantic coast), with a focus on European sea bass diet

The Bay of Aiguillon is a national French Nature Reserve of great importance for birds. Recently, the managers of the Reserve (ONCFS-LPO) paid attention to the influence of saltmarshes management on the nursery function for fish feeding in creeks at high tide. A study carried out from March to July 2012 aimed to evaluate the use of saltmarshes by fish juvenile fraction according to the mowing intensity in salt marshes surrounding creeks: ceased, irregular or annual mowing. This community approach was completed by a focus on the European sea bass Dicentrarchus labrax individual diet, vacuity index and growth, and the biomass of a main potential prey (the amphipod Orchestia gammarella). Whatever the mowing intensity, the juvenile fraction was very high for the main species, which were the grey mullet Liza ramada, the European sea bass, undetermined clupeid and the European flounder Platichthys flesus. Adult and subadult for these species were anecdotic or totally absent. Despite very different biomasses of amphipods between mown and natural sites, vacuity index, prey composition and their relative abundance in the diet of European sea bass juveniles were little different, contrary to their hypothetical growth (i.e. when assuming site fidelity), which appeared higher in non-mown site. The low distance between sampling sites could allow fish exchange over time between optimal and suboptimal creeks to feed on, as a hypothesis to explain such results. Because mowing was subsidized by European Union (EU) to favour open habitats for geese and maintain an economic activity, indirect impacts on nursery for fish called into question the appropriateness of such agro-environmental measure on natural habitats, and related fish nursery function.