Plaice Research Articles

Short-term discard survival and catch-related trauma in European plaice (Pleuronectes platessa) caught in the Baltic Sea by Danish seine during summer

Danish seine is an active fishing gear targeting demersal species, such as European plaice (Pleuronectes platessa, hencefort referred as plaice), a commercially important fish species in the North Sea, Skagerrak, Kattegat, and Baltic Sea. Danish seining is a relevant fishery in relation to exemption from the European Union landing obligation. Trials were conducted from a commercial fishing vessel during the summer with high air temperatures and sea salinity and marked salinity and temperature gradients (pycnocline). Video equipment was used to observe fish entering the seine. Captured fish were individually tagged and housed in livewells for ten days to observe short-term survival. Reflex impairments and external injuries were assessed after capture and at the end of the observation periods using reflex action mortality predictor (RAMP) and catch-damage index (CDI) methodologies. We found that plaice entered the seine late in the towing process and that 87 % of the assessed fish survived, after 10 days of observation. There was a significant difference in short-term survival curves for fish that had been subjected to more than 30 min of on-deck during the catch-sorting process relative to those that had remained on deck for 30 min or less. The association between the time on deck and RAMP scores after capture was also significant. External injuries were primarily minor bruises, fin fraying, and net marks and changed little from after capturing to the end of the observation period.

Can operational tactics compensate for weaker tensile properties of biodegradable gillnets?

This study aimed at discriminating between the effects of physical strain due to the interactive effect of gear operation and degradation, and degradation only, on the differences in breaking strength, strain, and stiffness at break of polybutylene succinate-co-adipate-co-terephthalate (PBSAT) (biodegradable) and PA6 (nylon) gillnet materials, and to compare the effect of fish species and resulting capture mode on catch efficiency for a roundfish species, Atlantic cod ( Gadus morhua), and a flatfish species, European plaice ( Pleuronectes platessa) in the Danish coastal gillnet fishery. The PBSAT meshes were much weaker than PA6 already at the start of the experiment. There were 58% (95% Confidence Interval (CI): 38%–79%) less cod and 32% (CI: 17%–49%) less plaice after 4 months in the PBSAT gillnets. We did not observe significant differences between the interactive effect of gear operation and degradation, and degradation only, and in capture modes. We conclude that reduction in catch efficiency results from a combination of weaker mechanical properties worsened by degradation during, e.g., transport and storage, and a species given shape and swimming ability.

Effect of temperature on growth, expression of growth regulating genes, and deformity development of juvenile European plaice (Pleuronectes platessa)

The flatfish European plaice is a demersal, temperate species and a candidate for marine aquaculture. To better understand growth and the mechanisms involved in growth regulation, juvenile plaice (initial mean weight ± SEM, 10.4 ± 0.1 g) were reared in triplicate rearing tanks at three different temperature: ambient (average of 8.6 °C), 12 °C and 16 °C, for 100 days. Interactions between growth, expression of growth regulating genes, and skeletal development were studied to determine optimal rearing conditions for juvenile plaice. Juvenile plaice grew fastest at 16 °C, followed by the 12 °C group. The condition factor was inversely correlated to increased temperatures and was highest in the 8.6 °C group. At the start of the experiment, 11% of the fish had vertebra deformities. Increasing temperature resulted in higher frequency and severity of malformations, and the 8.6 °C group had 8% less vertebra deformities at the end of the experiment compared to other two groups. The 12 °C and 16 °C groups had similar frequency of deformed fish, however, the 16 °C had more severe deformities, measured as number of deformed vertebrae per fish. Temperature affected gene transcript levels of ghr, igf-1, and igf-1r in muscle and liver tissue differently. Hepatic igf-1 transcript levels increased with increased growth and temperature. Muscular igf-1r transcript levels increased with increasing temperature in each sampling, indicating that igf-1r corresponded with muscular growth. Based on the present findings, a rearing temperature of 12 °C is recommended for on-growing of juvenile plaice.

Frozen storage procedures for salmon and plaice samples: Nutrient composition and implications for preservation.

We hypothesized that removing water from fish muscle homogenate by freeze-drying might be a cost-effective way to stabilize nutrients and allow higher temperatures for long-term frozen storage prior to analytical measurements. To test our hypothesis, fish muscle fillets from lipid-rich farmed Atlantic salmon (n=5) and lean wild-caught European plaice (n=5) were homogenized and fresh-frozen at -20 and -80°C. A subset of these samples was freeze-dried prior to further frozen storage at the respective temperatures. Using validated methods, vitamins, amino acids, and fatty acids were measured after a short time of storage (starting point) and up to 1year (endpoint), with intermediate analytical checkpoints of 1, 3, and 6months. Trends in the degradation of certain nutrients during the different frozen storage conditions are discussed. In general, by freeze-drying fish homogenate samples prior to frozen storage at -20°C for up to 1year, amino acids, vitamins, and fatty acids were stabilized in both salmon and plaice when compared to wet-frozen storage of the same samples, and storage at -80°C did not improve preservation of the freeze-dried samples. For wet-frozen samples, -80°C would be recommended for 1-year storage of fillet homogenate samples, even though several nutrients preserved well at -20°C. PRACTICAL APPLICATION: We present individual nutrient stability profiles in muscle homogenates from fatty fish (salmon) and lean fish (plaice) during different frozen storage conditions over time. Based on these data, freeze-drying followed by frozen storage at -20°C for at least 1year could be applied prior to analyses of amino acids, fat-soluble vitamins, water-soluble vitamins, and fatty acids. Of note is that freeze-drying followed by frozen storage before analysis led to slightly increased measurements of several fatty acids in plaice samples, possibly attributable to an increase in dry weight or an enhancement in extraction efficiency through freeze-drying.

Multi‐year monitoring shows higher species richness and diversity of fish assemblages in a Danish seagrass meadow as compared to neighbouring non‐vegetated areas

AbstractSeagrass meadows provide an important nursery and feeding habitat for fish, globally. However, limited data exist on how these vegetated coastal ecosystems affect local fish stocks over longer time periods. By means of beach seine hauling with a bio‐monitoring seine net, we collected fish data in Kronborg Bay (Denmark) over 4 years. The bay contains both vegetated and bare sediment areas in close proximity to Kronborg Castle in Elsinore and is part of the Øresund strait; a dynamic marine environment linking the Baltic Sea with the inner Danish waters (Kattegat). We investigated the biodiversity and fish abundance in a healthy seagrass meadow and compared it with a bare adjacent sediment area. We show that seagrass is important for fish species like the Atlantic cod, the two‐spotted goby, and the broadnosed pipefish. The seagrass meadow harboured more fish species and higher biodiversity, while the number of individuals was higher in the adjacent bare sediment area as a result of high abundances of lesser sand eel. Pilou's evenness and the Shannon‐Wiener index showed 2–4‐fold higher biodiversity in the seagrass meadow. The seagrass meadow harboured about 35% more fish species than the bare adjacent sediment. The Atlantic cod was almost entirely found in the seagrass meadow, while lesser sand eel that showed an overall increase in abundance in both habitats, represented the largest proportion of the total number of fish individuals (up to about 60%) and was mostly found on the bare adjacent sediment. Species abundance was analysed for changes over time, where, for example the European plaice showed an increase in abundance over the 4‐year period of investigation. Seagrass meadows can thus be very important for the Atlantic cod population in the Øresund strait and generally for local fish productivity, abundance and diversity.

European plaice (Pleuronectes platessa) in aquaculture – Nutritional, chemical, and physicochemical quality compared to wild stocks

European plaice (Pleuronectes platessa) is among Europe's top-consumed fish species, but wild stocks fluctuate and change their habitat due to drastic changes in climate. Their potential in aquaculture is under consideration, and therefore multiple quality aspects have been evaluated in this study. The chemical composition, nutritional profile, and physicochemical properties of European plaice (Pleuronectes platessa) from aquaculture and wild origin (Norwegian west-coast) and differences between female and male farmed individuals were studied. Differences between farmed and wild fish were found for the proximate composition, nutritional profile, and physicochemical attributes. Farmed fish generally had paler color (higher L*; 78.7 ± 4.2) but showed reduced water holding capacity (WHC; 80.3 ± 8.1%), but a firmer fillet texture compared to wild plaice. Farmed fish had significantly higher lipid and lower ash contents than wild individuals. Farmed fish's free amino acid (FAA) content (265.6 ± 59.0 mg/ 100 g) was significantly higher than in wild fish (89.72 ± 43.6 mg/ 100 g), especially the taste contributing FAA glutamate, glycine, alanine, and tyrosine. However, large individual varieties in FAA were observed within farmed and wild specimens. Farmed fish's fatty acid (FA) profile reflects the feed's composition. The overall quality of farmed European plaice was comparable to wild individuals with an excellent nutritional profile. Gender comparisons in farmed fish has shown that females were paler (higher L*) and showed higher hue (h) values, lower color saturation (Chroma, C), and yellowness (a*) compared to males. No apparent difference in texture was found, and no correlations between WHC and pH nor WHC and water content were detected between females and males. Farmed male individuals had higher lipid (2.35 ± 1.5%) and protein (16.97 ± 1.1%) concentrations compared to females (1.72 ± 1.1%; 15.52 ± 1.7%). The overall findings of this study are promising to further investigate this species for cultivation as a sustainable food resource.

Disappearing fish: Grey seal depredation in a Baltic net fishery

Grey seals (Halichoerus grypus) in the Baltic Sea commonly attempt to steal fish captured in net fisheries. Seal depredation reduces economic yields for small-scale net fishers in a region already highly impacted by the collapse of important fish stocks. Visible damages in looted nets consist of injured fish with bite marks, or holes in the gear, but additional losses from seals eating entire fish without leaving a trace can often remain unnoticed. In this study, we estimated the daily rates of injured and of stolen fish in a commercial gillnet fishery operating off coast of Bornholm in the Central Baltic Sea in 2021–2022. Our results show that the Atlantic cod (Gadus morhua) is generally preferred over other target species [here, European plaice (Pleuronectes platessa), European flounder (Platichthys flesus), and turbot (Scophthalmus maximus)]. Although the observed ratio of 5.65 cods disappearing for each cod retrieved with seal bite marks is similar to a study from the 2000’s, we show that average daily cod disappearance rates are linked to the duration a gear is left soaking in the same location.

An assessment of post-capture condition and survival of Rajidae caught in fixed nets

Skates (Rajiformes: Rajidae) are commercially and ecologically-important elasmobranchs captured in targeted and mixed fisheries globally. Many species are of conservation concern and are subject to high levels of discarding. They are currently exempt from the European Union’s landing obligation due to evidence of high discard survival, although the bulk of this evidence comes from mobile gear fisheries. Improved evidence on survival after discarding from fixed gears is necessary. We assessed immediate survival rates and post-capture condition (injury, reflex impairment, and vitality) of four skate species commonly discarded from seasonal Dover sole, Solea solea and plaice, Pleuronectes platessa gillnet fisheries in the Irish Sea and Bristol Channel, UK. We also modelled the relationship between a suite of environmental and operational fishing variables to the condition of thornback skate, Raja clavata. This is the dominant skate captured as bycatch and is classified as near threatened by the IUCN due to declining populations trends. At-vessel survival on gear hauling was high for all species (R. clavata = 99.43%, R. montagui = 100%, R. microocellata = 100%, R. brachyura = 100%). Post-capture condition of R. clavata was size-dependent, with larger skates demonstrating higher levels of injury and reflex impairment and poorer vitality. Higher vitality in smaller individuals and strong negative effects of aerial exposure on skate vitality highlight the likely benefits of prioritising discarding of unwanted catch upon gear hauling. This may maximise survival and future reproductive potential and facilitate population recovery.

Spatial and temporal variability in larval connectivity of North Sea plaice Pleuronectes platessa between spawning grounds and coastal European nurseries

Annual year-class strength in North Sea plaice Pleuronectes platessa Linnaeus, 1758 appears to be determined by the connectivity of eggs and larvae between open-sea spawning grounds and coastal nursery areas. Hydrodynamic modelling studies indicate that coastal nurseries can be supplied with larvae from multiple offshore spawning locations. To verify this, we compared relative size-frequency distributions of demersal juvenile plaice just after larval immigration between coastal nurseries as a proxy for larval origin. During 12 yr, up to 21 stations in the Dutch coastal zone and international Wadden Sea were visited and sampled at the beginning of May at the end of larval immigration. The results of the size-frequency analysis showed 2 distinct clusters of stations. The first cluster included all stations along the Dutch coast and Wadden Sea up to Wangerooge in the German East Frisian Wadden Sea, most likely dominated by supply from spawning grounds in the Southern Bight, with contributions from the English Channel and the Dogger Bank. The second cluster included all stations in the North Frisian Wadden Sea, most likely supplied from spawning grounds in the German Bight and near the Dogger Bank. The higher interannual variability in the first cluster might be caused by a larger variability in the relative contributions from multiple spawning areas (English Channel, Southern Bight, Dogger Bank). The comparison of the relative size-frequency distributions at the end of larval immigration introduced in this study may also be a useful tool for the validation of connectivity modelling studies in other areas and for other species.

Long-term change in a North Sea inshore fish assemblage between 1899-1913 and 2018-2019

Marine communities have been impacted by human activities for centuries, yet historical data are rarely incorporated into modern conservation efforts and restoration targets. For inshore waters, survey data sets are typically lacking because they extend back by only a few decades, despite their ecological significance as nursery grounds for many fish species. We investigated long-term change in a demersal fish assemblage from inshore waters of the Northumberland coast (UK). We collated unique historical data (1899-1913) that were sampled using a wooden beam trawl during scientific trawling investigations, shortly after the onset of widespread mechanised trawling in the North Sea. Twelve decades later (2018-2019), we re-surveyed the same bays using a modern otter trawl. The results revealed marked declines in the abundance and diversity of the entire fish and flatfish assemblage as well as among individual species. Elasmobranchs and formerly abundant species such as grey gurnard Eutrigla gurnardus were completely absent in contemporary surveys, while dab Limanda limanda and plaice Pleuronectes platessa were the most dominant species in both periods. Changes were also detected in the size distributions of the entire fish and flatfish assemblages, with proportionally fewer large individuals recorded in contemporary surveys. These findings suggest that over a century of trawling and climate change, combined with pollution, habitat alteration and increased predation risk are likely contributors to changes in the inshore fish assemblage. This work provides further evidence of long-term decline in North Sea inshore waters and offers an invaluable benchmark for improving coastal ecosystem status.

Diphyllobothrium sp. and Other Parasites of Migrating and Rare Fish Species in the Southern Baltic Sea and Coastal Waters, Poland.

The present study is the first to analyse the parasite fauna of sole Solea solea, dab Limanda limanda, hake Merluccius merluccius, whiting Merlangius merlangus, and plaice Pleuronectes platessa in the Pomeranian Bay, as well as saithe Pollachius virens from the Szczecin Lagoon (Poland). The aim of this study was to determine the occurrence of parasites in migrating and rare fish in the Pomeranian Bay and the Szczecin Lagoon and to determine the composition of the diet of these fish. The fish for analysis were obtained in the years 2010-2019. The typical marine nematode Capillaria (Procapillaria) gracilis, rarely recorded in Poland, was found, in addition to the following parasites: Ichthyophonus hoferi, Trichodina jadranica, Diphyllobothrium sp., Dichelyne (Cucullanellus) minutus, Raphidascaris acus, Anisakis simplex, Contracaecum osculatum, Hysterothylacium aduncum, Pseudoterranova decipiens, and Echinorhynchus gadi. Because the fish species analysed in the study are not typically present in the Baltic (with the exception of plaice), and because we do not know how long they feed while they are in the Baltic, we cannot be certain which parasites they acquired in the water bodies analysed in the study and which were introduced during the migration of fish. Although these fish are outside of their normal geographic range (except for plaice), in the new environment, there were enough suitable intermediate hosts for the parasites of these fish to complete their life cycle and survive.

Coupling state‐of‐the‐art modelling tools for better informed Red List assessments of marine fishes

Abstract In the face of biodiversity loss worldwide, it is paramount to quantify species' extinction risk to guide conservation efforts. The International Union for the Conservation of Nature (IUCN)'s Red List is considered the global standard for evaluating extinction risks. IUCN criteria also inform national extinction risk assessments. Bayesian models, including the state‐of‐the‐art JARA (‘Just Another Red List Assessment’) tool, deliver probabilistic statements about species falling into extinction risk categories, thereby enabling characterisation and communication of uncertainty in extinction risk assessments. We coupled the state‐of‐the‐art VAST (‘Vector Autoregressive Spatio‐Temporal’) modelling tool and JARA, for better informed Red List assessments of marine fishes. In this framework, VAST is fitted to scientific survey catch rate data to provide indices to JARA whose uncertainty is propagated to JARA outcomes suggesting extinction risk categories (under the population reduction criterion). In addition, VAST delivers a valuable habitat assessment to better understand what may be driving extinction risk in the study region. Here, we demonstrate the coupled VAST‐JARA modelling framework by applying it to five contrasting North Sea species, with or without a quantitative stock assessment and with different conservation statuses according to the latest global Red List assessments. The North Sea application coupled with previous assessments and studies suggest that, among the three elasmobranchs, starry ray is in most need of urgent research (and conservation actions where appropriate), followed by spurdog, while lesser‐spotted dogfish is increasing in biomass. Moreover, both the VAST‐JARA modelling framework and previous research indicate that, while European plaice is not of conservation concern, cod has likely met the IUCN criteria for being listed as Endangered recently. Synthesis and applications. The predictions of the VAST‐JARA modelling framework for North Sea species, including JARA output and VAST habitat assessment, constitute valuable supporting information to make interpretations based on Red List guidelines, which will help decision‐makers in their next North Sea Red List assessment. We foresee applications of the modelling framework to assist Red List assessments of numerous marine fishes worldwide. Our modelling framework has many potential advantageous uses, including informing resource management about climate change impacts on species' extinction risks.

The role of temperature in vitality and survival assessments of beam-trawled and discarded European plaice (Pleuronectes platessa).

Thermal stress can influence the recovery of fish released after capture. Vitality assessments using reflex and behavioural responses require that responses can be observed reliably, independent of temperature. Here, we tested whether reflex and behavioural impairment and survival of beam-trawled and discarded European plaice (Pleuronectes platessa) are independent from seasonal air and water temperature deviations. In total, 324 beam-trawled plaice (n = 196 in summer and n = 128 in winter) were exposed to two air temperature treatments and two water treatments (i.e. modified and ambient temperatures for both). The modified treatments (i.e. cooled in summer, warmed in winter) represent the thermal shock a fish may experience when being returned to the water. All reflexes and tested behaviours were affected by ambient temperature, with high impairment noted in summer. None of the reflexes were affected by temperature shocks alone, only body flex was. Body flex was highly impaired under every exposure combination. Fish size and duration of air exposure further influenced impairment of reflexes such as head complex and tail grab. More generally, post-release survival was assessed as 21% [95% CI: 16-28%] in summer and 99% [97-100%] in winter. Beam trawling in summer is likely to induce high reflex impairment and mortality in discarded plaice, and therefore spatial-temporal mitigation approaches should be prioritized over control of on-board temperatures.

Optimizing the prediction of discard survival of bottom-trawled plaice based on vitality indicators.

Predicting the discard survival of aquatic animals after fisheries capture using vitality indicators (i.e. individual scores or indices of physical condition) is a resource-efficient approach compared to estimating discard survival from captive observation. But such indicators do not always lead to accurate and robust predictions. Individual scores of reflex impairments and injuries are typically given the same weight when being aggregated into an index, while some reflexes or injuries may contribute to mortality more than others. This study established an analytical methodology and created an index based on differential contributions of individual reflexes and injuries to optimize the prediction of discard survival of bottom-trawled European plaice (Pleuronectes platessa). The optimization procedures were applied to a dataset from vitality assessment of 1122 undersized plaice caught during 16 commercial fishing trips and 58 gear deployments in Belgium and Denmark. As welfare indicators, we considered and evaluated against post-capture survival of plaice: original vs. optimized reflex impairment and injury (R&I) index, number of absent reflexes, number of present injuries, number of absent reflexes and present injuries, categorical vitality score and individual reflex and injury scores. These were used in eight candidate generalized linear models (one without any vitality indicator) as explanatory variables to predict survival, with or without biological, environmental, technical and operational covariates, either at the individual fish or trip level. Bruising to the head and body were the most relevant predictors. The optimized R&I index did not perform better than any other vitality indicator, and all the indicators performed poorly in predicting survival probability both at the fish and trip levels without information on air exposure and seawater temperature. This means that they cannot be considered to be independent measures. The categorical vitality score provided a viable alternative to the more labour-intensive, scoring method of reflex responsiveness. Use of reflexes as proxies may not be accurate when they are not independent of environmental, biological or technical variables.

European plaice movements show evidence of high residency, site fidelity, and feeding around hard substrates within an offshore wind farm

Abstract Offshore wind farms (OWFs) are expanding rapidly in the North Sea, often creating spatial conflicts with fisheries. Managing such conflicts requires knowledge on the impact of OWFs on the spatial distribution and movement behaviour of fished species. However, such knowledge is still lacking, especially for soft sediment fish such as flatfish, which are vital fisheries resources in the region. Therefore, we used acoustic telemetry to examine the spatial behaviour of European plaice in relation to an OWF and its structures. In a small study area (1.37 km2), we observed high residency for plaice around the turbines and scour protection layer (SPL), which consists of large rocks around the turbine foundation. The fish primarily resided on sandy sediments near the hard substrates, but showed a diurnal pattern of proximity to the turbine, being closer during the day. Considering their trophic ecology, these findings suggest that plaice moves towards the SPL for feeding opportunities on the hard substrate, potentially leading to increased ecological fish production within OWFs. Although most plaice moved away from the OWF in winter, likely towards spawning grounds, many exhibited high site fidelity returning to the study area after the winter migration. OWFs thus offer protection from fishing mortality as “closed” feeding grounds in spring and summer, but not during winter spawning migrations, which may result in spillover effects. These insights should inform local fisheries management in relation to plaice movement within and around OWFs.

Insight to the diversity of Photobacterium spp. isolated from European plaice (Pleuronectes platessa) based on phylogenetic analysis, phenotypic characterisation and spoilage potential

This study aimed to explore the diversity of fifty-four Photobacterium strains isolated from muscle tissue of European plaice (Pleuronectes platessa) caught at different fishing seasons and stored 14-days under various conditions. Single phylogenetic markers (16S rRNA, gapA, gyrB and recA) and multilocus sequence analysis (MLSA) were employed to classify isolates at species level. Furthermore, intra- and interspecies variability in the phenotypic traits, maximum specific growth rate (μmax) and spoilage potential of the Photobacterium isolates were investigated. The isolates were classified into the P. iliopiscarium (53.7 %), P. phosphoreum (40.7 %) and P. piscicola (5.6 %) clades using MLSA. Two housekeeping genes, gyrB and recA, exhibited a consistent phylogenetic relationship with MLSA, suggesting that they might be used as individual phylogenetic markers for the Photobacterium genus. Intra- and interspecies variability in the expression of phenotypic characteristics and the production of trimethylamine (TMA), inosine (HxR), and hypoxanthine (Hx) were observed. A growth optimum temperature for P. iliopiscarium was approximately 20 °C, while those for P. phosphoreum and P. piscicola were closer to 15 °C. All isolates exhibited the highest growth density at 1.5 % NaCl, followed by 0.5 %, 3 %, and 6 % NaCl. However, P. phosphoreum demonstrated a higher NaCl tolerance than the other two species. Although, the high CO2 atmosphere significantly inhibited the growth of all strains at 4 °C, P. phosphoreum and P. piscicola showed higher growth density at 15 °C than P. iliopiscarium. Notably, all strains demonstrated H2S production. The μmax varied considerably within each species, highlighting the significance of strain-level variability. This study demonstrates that P. iliopiscarium and P. piscicola, alongside P. phosphoreum, are efficient TMA-, HxR-, Hx-, and H2S-producers, suggesting their potential contribution to synergistic off-odour generation and spoilage. Moreover, the Photobacterium isolates seem to exhibit diverse adaptations to their environments, resulting in fluctuated growth and spoilage potential. Understanding intra- and interspecies variability will facilitate modelling seafood spoilage in microbial risk assessments and developing targeted hurdles to prolong products' shelf-life.

Potential impacts of the restoration of coastal and estuarine nurseries on the stock dynamics of fisheries species

Coastal and estuarine (CE) areas are essential fish habitats; they act as nurseries for a large proportion of species of fisheries interest but face high levels of cumulative anthropogenic pressures. A comprehensive analysis of the impacts of CE nursery habitat degradation at the population scale for exploited fish species is still lacking. Our study aims to assess the effects of CE nursery habitat restoration for four species of main fisheries of interest in the Eastern English Channel (EEC): sole (Solea solea), plaice (Pleuronectes platessa), whiting (Merlangius merlangus) and seabass (Dicentrarchus labrax). A generic age- and stage-based population model representing the dynamics of exploited populations and integrating the dependence of recruitment on juvenile habitats was used. This model allowed us to evaluate the combined effect of nursery degradation and fishing pressure on stock dynamics. The model was parameterized for each of the four species based on stock assessment outputs in the EEC and literature and then used to simulate equilibrium states under different habitat restoration scenarios. These scenarios were built using previous estimates of both surface area loss and decrease in marine juvenile fish density in CE habitats facing anthropogenic pressures in the EEC. Surface area and quality restoration enhanced both biomass and sustainable catch levels for the four species in the EEC. The species with higher concentrations in shallow nursery areas were the most sensitive to habitat restoration. The response also depended on life history traits, i.e., species with lower resilience to fishing pressure (i.e., steepness) exhibited a stronger response to habitat quality scenarios.

Fast and User-Friendly Detection of Flatfish Species (Pleuronectes platessa and Solea solea) via Loop-Mediated Isothermal Amplification (LAMP).

The detection of a Cytochrome b gene (cytb) for species differentiation in fish is intensively used. A fast alternative to expensive and time-consuming DNA barcoding is loop-mediated isothermal amplification (LAMP) in combination with efficient readout systems. For this reason, we developed LAMP assays for rapid species detection of Pleuronectes platessa and Solea solea, two economically important flatfish species in Europe that are prone to mislabeling. Species-specific primer sets targeting cytb were designed, and LAMP assays were optimized. With the optimized LAMP assays, we were able to detect up to 0.1 and 0.01 ng of target DNA of P. platessa and S. solea, respectively, and in each case up to 1% (w/w) of target species in mixtures with nontarget species. For future on-site detection, a lateral flow assay and a pocket-sized lab-on-phone assay were used as readout systems. The lab-on-phone assay with the S. solea specific primer set revealed cross-reactivity to Solea senegalensis. The assay targeting P. platessa proved to be highly specific. Both assays could be performed within 45 min and provided rapid and easy detection of fish species.

The application of microwave and ultrasound technologies for extracting collagen from European plaice by-products

This study’s main aim was to utilize green extraction protocols to recover collagen from by-products originating from European plaice. Moreover, the objective was to evaluate pre-treatments, the composition of the up-cycled product as well as to identify the most promising by-product fraction. Microwave (MAE) and ultrasound-assisted extractions (UAE) were performed on untreated, pre-treated (salt-washed or enzymatic hydrolysis) fractions of backbones, skins, and heads. Both MAE and UAE were performed for 15 and 35 min. After pre-treatment and extraction, the quality and yield of products were evaluated. Protein and collagen concentration, as well as amino acid profiles, were measured. Skins deliver significantly higher yields of collagen and protein than heads and backbones (p < 0.05). Enzymatic hydrolysis resulted in the highest collagen yields for skins (77%), while salt-washing gave the highest results for backbones (43%) and heads (41%) regardless of extraction method and time. Total and free amino acid profiles differed between the three fractions, with backbones and heads showing overall more similarity in composition compared to skins. The study showed that MAE and UAE technologies are suitable for generating collagen from marine by-products. Additional research is recommended to optimize pre-treatment and extraction for skin, as most promising collagen supplier.

The genome sequence of the European plaice, Pleuronectes platessa (Linnaeus, 1758).

We present a genome assembly from an individual Pleuronectes platessa(the European plaice; Chordata; Actinopteri; Pleuronectiformes; Pleuronectidae). The genome sequence is 687.4 megabases in span. Most of the assembly is scaffolded into 24 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 17.4 kilobases in length.