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Winter flounder Pseudopleuronectes americanus (Walbaum 1792) are a coastal flatfish species of economic and cultural importance that have dwindled to <15, % of their historic abundance in the southern New England/Mid‐Atlantic region of the United States, with evidence indicating near‐extirpation of certain local populations. This species exhibits intricate behaviors in spawning and migration that contribute to population complexity and resilience. These behaviors encompass full or partial philopatry to natal estuaries, the generation of multiple pulses of larval delivery, and partial migration. The patterns of genetic diversity within and among estuaries and cohorts presented here carry important implications in understanding the susceptibility to demographic shocks, even if the full extent of genetic diversity within and among winter flounder stocks on the US East Coast remains unresolved. Our findings reveal connectivity between estuaries in Long Island, New York, suggesting the potential for genetic rescue of depleted subpopulations. Family reconstruction and relatedness analysis indicate that split cohorts and migration contingents are not the result of genetically distinct lineages. We found no evidence for genetic structure separating these groups, and in some instances, we were able to detect closely related individuals that belonged to different migratory contingents or cohorts. Characterizing the spatial and behavioral organization of this species at the population level is crucial for comprehending its potential for recovery, not only in terms of biomass but also in reinstating the complex population structure that supports resilience. The search for generality in winter flounder spawning and migration behavior remains elusive, but perhaps the lack of generalities within this species is what has allowed it to persist in the face of decades of environmental and anthropogenic stressors. [ABSTRACT FROM AUTHOR]

Stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) are ubiquitous ecological tracers used to elucidate an organism's diet and habitat. However, the application of stable isotope ratios to reconstruct a consumer's ecology relies upon accurate rates for isotopic turnover at both a tissue and species-specific level. This study estimated isotope turnover rates and trophic discrimination factors in four different tissues (liver, digestive tissue, muscle, and skin) with variable metabolic activity in winter flounder Pseudopleuronectes americanus using a controlled diet-switch experiment. Differences in half-lives were noted among the tissues and between the experimental diets for both δ15N and δ13C. The experimental diets of krill and mysis had variability in nutritional composition, resulting in similar turnovers in δ15N but slower turnovers in δ13C for fish fed krill. Turnovers in both δ15N and δ13C were strongly influenced by metabolism, with the contribution reaching up to 98%, as fish exhibited minimal overall growth. The results of this study demonstrate the importance of considering differences in the catabolic activity of tissue maintenance for fish exhibiting minimal growth, as well as differences in metabolic assimilation of dietary sources that vary in their protein and lipid contents. [ABSTRACT FROM AUTHOR]

As the impacts of climate change become more severe throughout the global oceans, fisheries managers will be increasingly challenged to rebuild stocks exhibiting declining productivity. In such cases, detailed knowledge of species life history will be necessary to both restrict harvest and manage other environmental conditions, where possible, that impact survivorship. A current example of these challenges, the Southern New England/Mid‐Atlantic Bight winter flounder stock remains in a persistently depleted state due to a combination of past harvest and the effects of climate change mediated through increased predation. To explore the recovery capacity of a subpopulation of this stock, a life‐cycle model was fit to 29 year classes of stage‐specific winter flounder data from surveys conducted in Narragansett Bay, Rhode Island and used to project future subpopulation abundance. Supporting a prevailing hypothesis, the results indicated that environmental factors influencing juvenile mortality were largely responsible for inhibiting recovery. Furthermore, recovery of the subpopulation to past levels of abundance was determined to be unlikely even under optimistic future conditions resulting from aggressive management interventions. Taken together, the findings of this work pose important questions regarding the realism of assessing climate‐challenged populations against biological reference points set under past environmental regimes and the degree to which harvest restrictions to promote recovery of such stocks should be allowed to limit warm‐water fisheries thriving in a warming ocean. [ABSTRACT FROM AUTHOR]

Stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) are ubiquitous ecological tracers used to elucidate an organism’s diet and habitat. However, the application of stable isotope ratios to reconstruct a consumer’s ecology relies upon accurate rates for isotopic turnover at both a tissue and species-specific level. This study estimated isotope turnover rates and trophic discrimination factors in four different tissues (liver, digestive tissue, muscle, and skin) with variable metabolic activity in winter flounder Pseudopleuronectes americanus using a controlled diet-switch experiment. Differences in half-lives were noted among the tissues and between the experimental diets for both δ15N and δ13C. The experimental diets of krill and mysis had variability in nutritional composition, resulting in similar turnovers in δ15N but slower turnovers in δ13C for fish fed krill. Turnovers in both δ15N and δ13C were strongly influenced by metabolism, with the contribution reaching up to 98%, as fish exhibited minimal overall growth. The results of this study demonstrate the importance of considering differences in the catabolic activity of tissue maintenance for fish exhibiting minimal growth, as well as differences in metabolic assimilation of dietary sources that vary in their protein and lipid contents.

The winter flounder, Pseudopleuronectes americanus , synthesizes a variety of alpha-helical antifreeze proteins (AFPs) that adhere to ice and inhibit its growth. The best studied of these is AFP6, which is a 37-residue protein abundant in the flounder blood plasma during winter. Curcumin from the turmeric plant (Curcuma longa) was found to interact with AFP6 in aqueous solutions, resulting in measurable changes in the curcumin, but not in the protein. Specifically, the secondary structure and unfolding of synthetic AFP6, shown by circular dichroism, appeared to be unaffected by curcumin. In contrast, the peak absorbance of curcumin shifted and increased in the presence of AFP6, and the maximum fluorescence emission was greater and blue shifted. These results also suggested the possibility of AFP6 detection by curcumin fluorescence. Synthetic AFP6 did not interact with Coomassie blue, silver or a commercial fluorescent stain following electrophoresis; however, the change in curcumin fluorescence upon binding to electrophoresed AFP6 resulted in a fluorescent signal, which was also detected upon interaction with purified natural AFP and flounder blood plasma containing the protein. Thus, aqueous curcumin can be used for the direct detection of AFP6 and curcumin binding could provide new avenues for the study of this protein. • Aqueous curcumin binds to the predominant antifreeze peptide (AFP6) of winter flounder. • The absorbance and fluorescence spectra of curcumin are altered when it interacts with AFP6. • The secondary structure and melting transition of AFP6 appear unchanged in the presence of curcumin. • Curcumin binding allows detection of AFP6 following gel electrophoresis, whereas typical stains do not. [ABSTRACT FROM AUTHOR]

Winter flounder (Pseudopleuronectes americanus) is a North Atlantic flatfish that inhabits cold-water environments already affected by global warming. Flatfishes are particularly sensitive during their juvenile stage to a phenomenon known as temperature-dependent sex determination (TSD). In this study, we hypothesized that many genes involved in the steroidogenesis pathway are already expressed at the larval stage in winter flounder and that temperature conditions may influence this pathway prior to the juvenile stage, which is usually considered the TSD-sensitive period. We also hypothesized that temperature effects on the steroidogenesis pathway may carry over from the larval to the juvenile stage. We surveyed three cohorts issued from three different spawning events during spring. Rearing temperature and salinity conditions followed seasonal conditions in the St. Lawrence Estuary (Québec, Canada). As a result, cohorts were exposed to different temperature regimes during egg and larval development. Once metamorphosis occurred, all juveniles were held at a stable temperature of 10.1 ± 0.8 °C. Larvae were sampled at 20, 30, and, 40 days post-hatching and juveniles at one and two months post-metamorphosis. RNA was extracted from these individuals and then sequenced. Transcriptome analysis showed clear differentiation between larvae and juveniles. Gene expression patterns showed that the steroidogenesis pathway, including genes involved in gonadal differentiation, was influenced by temperature during larval development, which indicates that sexual determination at the cellular level is an early process in winter flounder development. Carry-over effects of larval rearing temperature conditions were present at the juvenile stage, with an increased number of genes involved in the steroidogenesis pathway being affected. Altogether, our study highlights the important role of larval development and temperature exposure on the transcriptome of winter flounder., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Stock size estimates used in stock–recruitment models often assume that reproductive output per individual is equal despite evidence that larger, older spawners contribute diverse spawning behaviors and disproportionately more to reproductive output. This is concerning since depleted population states often coincide with a compromised age structure and increased control of extrinsic forces (environmental conditions or predator–prey dynamics) on stock productivity. In this study, parameterizations of the stock–recruitment relationship for Winter Flounder Pseudopleuronectes americanus, which incorporated covariate metrics describing age structure, temperature, and predation, were compared to identify primary drivers across area‐specific data sets that are included in recent regional stock assessments. Four of the six data sets resulted in a top‐ranked model that incorporated an age structure metric; however, the age structure metric model was alone in the pool of top‐ranked models for only two of these scenarios. In addition, one data set resulted in a base Ricker model, and one resulted in a model that incorporated a predator index. Finally, wavelet analysis identified significant coherence between fishing mortality rate (F) and spawning stock biomass (SSB) for Winter Flounder, which switched from an out‐of‐phase state to an in‐phase state during the 1990s. If the relationship between these model‐derived estimates of F and SSB reflects dynamics of the Winter Flounder population, it would have strong implications for management efforts. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore an emerging discipline addressing the impact of anthropogenic noise on larval stages of marine organisms. We assessed the influence of boat noise on the feeding behaviour of the pelagic larvae of winter flounder (Pseudopleuronectes americanus, Walbaum, 1792). The hypothesis was that boat noise influences the feeding behaviour of P. americanus flounder larvae independently of prey density. Aquaria containing P. americanus larvae were placed in water baths in which boat noise was diffused for the "noise" treatment and compared to control aquaria with no sound emissions. Larvae were filmed using cameras placed above the aquaria and their behaviour was recorded. Larvae exposed to anthropogenic noise displayed significantly fewer hunting events than controls, and their stomach volumes were significantly smaller. This noise effect was the same at all prey densities used, suggesting that larval feeding behaviour is negatively impaired by anthropogenic noise. [ABSTRACT FROM AUTHOR]

Antifreeze proteins (AFPs) bind to ice in solutions, resulting in non-colligative freezing point depression; however, their effects on ice nucleation are not well understood. The predominant plasma AFP of winter flounder (Pseudopleuronectes americanus) is AFP6, which is an amphiphilic alpha helix. In this study, AFP6 and modified constructs were produced as fusion proteins in Escherichia coli , subjected to proteolysis when required and purified prior to use. AFP6 and its recombinant fusion precursor generated similar thermal hysteresis and bipyramidal ice crystals, whereas an inactive mutant AFP6 produced hexagonal crystals and no hysteresis. Circular dichroism spectra of the wild-type and mutant AFP6 were consistent with an alpha helix. The effects of these proteins on ice nucleation were investigated alongside non-AFP proteins using a standard droplet freezing assay. In the presence of nucleating AgI, modest reductions in the nucleation temperature occurred with the addition of mutant AFP6, and several non-AFPs, suggesting non-specific inhibition of AgI-induced ice nucleation. In these experiments, both AFP6 and its recombinant precursor resulted in lower nucleation temperatures, consistent with an additional inhibitory effect. Conversely, in the absence of AgI, AFP6 induced ice nucleation, with no other proteins showing this effect. Nucleation by AFP6 was dose-dependent, reaching a maximum at 1.5 mM protein. Nucleation by AFP6 also required an ice-binding site, as the inactive mutant had no effect. Furthermore, the absence of nucleation by the recombinant precursor protein suggested that the fusion moiety was interfering with the formation of a surface capable of nucleating ice. [Display omitted] • Antifreeze proteins and other proteins can inhibit AgI-induced ice nucleation. • A winter flounder antifreeze protein can shift directly from inhibitor to nucleator. • Conversion to an ice nucleator is specific to the antifreeze protein. [ABSTRACT FROM AUTHOR]

The physical nature underlying intermolecular interactions between two rod-like winter flounder antifreeze protein (AFP) molecules and their implication for the mechanism of antifreeze function are examined in this work using molecular dynamics simulations, augmented with free energy calculations employing a continuum solvation model. The energetics for different modes of interactions of two AFP molecules is examined in both vacuum and aqueous phases along with the water distribution in the region encapsulated by two antiparallel AFP backbones. The results show that in a vacuum two AFP molecules intrinsically attract each other in the antiparallel fashion, where their complementary charge side chains face each other directly. In the aqueous environment, this attraction is counteracted by both screening and entropic effects. Therefore, two nearly energetically degenerate states, an aggregated state and a dissociated state, result as a new aspect of intermolecular interaction in the paradigm for the mechanism of action of AFP. The relevance of these findings to the mechanism of function of freezing inhibition in the context of our work on Antarctic cod antifreeze glycoprotein (Nguyen et al., Biophysical Journal, 2002, Vol. 82, pp. 2892-2905) is discussed. (C) 2004 Wiley Periodicals, Inc.

Winter Flounder (Pseudopleuronectes americanus) ranges from southern Labrador to Chesapeake Bay. In the southern Gulf of St. Lawrence (NAFO Div. 4T; sGSL), Winter Flounder tends to be distributed in shallow, near shore areas where it is fished primarily for bait. A total allowable catch was first instituted in 1996 at 1,000 t. Following the most recent assessment in 2011, the TAC was reduced to 300 t and has been in effect for the period 2012 to 2016. Winter Flounder is currently caught in a relatively small directed fishery concentrated mainly around the Magdalen Islands with landings ranging from 190 to 320 tonnes over the past 10 years. Abundance indices from a research survey show that there has been a decrease in the size distribution of the Winter Flounder stock with percentages of fish >= 25 cm (minimum size limit for the fishery) decreasing from an average of 85% during 1971 to 1975 to 30% during 2011 to 2015. Estimates of spawning stock biomass (SSB) were highest in the period from 1975 to 1994 at an average of 356,100 t (median). Over the recent period, the SSB estimate has declined to 235,700 t in 2003 and 76,270 t in 2016. The proportion of the SSB represented by older fish (5+) has also decreased over time. Based on a population model, the estimates of natural mortality have recently increased for young fish (ages 2 to 4) and continually increased for older fish (aged 5+). The instantaneous fishing mortality rate is estimated to be low to very low for all ages. The stock is considered to have been below the LRP since 2006. In 2016, the estimated SSB was 54% of the LRP. Projections at catch levels of 0 t, 100 t, and 300 t show no perceivable difference in stock trends over the next five years. Fishing mortality is a very small proportion of the total mortality of Winter Flounder in the southern Gulf of St. Lawrence and natural mortality is estimated to be the dominant factor affecting abundance. The contraction in size structure of Winter Flounder, the decline in the estimated size at 50% maturity, and the decline in abundance indices of the previously abundant commercial sized group are consistent with a stock experiencing very high levels of mortality. [ABSTRACT FROM AUTHOR]

Highlights • Male winter flounder spawning time and maturity size differs among U.S. stocks. • Male winter flounder make large reproductive investments relative to other flounder. • Male winter flounder maturity varies more in relation to size than age. • Spermatozoa are present in nearly all mature classes. • No evidence of male winter flounder skipped spawning was found in any of the U.S. stocks. Abstract Winter flounder, Pseudopleuronectes americanus , were collected from three fishery stocks in the United States (U.S.) during 2009–2013 to describe spermatogenesis. Spermatogenesis included rapid, synchronous transitions during autumn from mitotic spermatogonia to meiotic spermatocytes, then to haploid spermatids, and the release of spermatozoa into lobule lumen. As these transitions occurred several months prior to the spring spawning season, maturity of the testes are a poor indicator of spawning season, however, individuals can be readily evaluated prior to the spawning season for evidence of skipped spawning. Throughout this process, the gonad weight increased dramatically, with spawning-season maxima from 11 to 17% relative to individual somatic weight, suggesting considerable reproductive investment relative to other flatfishes. Fish condition also cycled seasonally, which indicated that males follow a capital breeding pattern that has been reported for female winter flounder. The timing of spermiogenesis was very similar in the fish among each U.S. stock (Southern New England [SNE], Georges Bank [GB], and the Gulf of Maine [GOM]) and published data from coastal Newfoundland, even though U.S. winter flounder spawned earlier in spring than fish in the Canadian stock. Male maturity varied in relation to both size and age, and over time, in patterns similar to those reported for female winter flounder, but at smaller and younger sizes than females. These intra-specific variations in reproductive seasonality, maturation, and skipped spawning suggest that winter flounder have the potential to adaptively respond to a dynamic environment in a region where ocean warming is occurring rapidly. [ABSTRACT FROM AUTHOR]

Measuring fish condition should link ecosystem drivers with population dynamics, if the underlying physiological basis for variations in condition indices are understood. We evaluated traditional (K, Kn, hepatosomatic index, gonadosomatic index, energy density, and percent dry weight of muscle (%DWM) and liver (%DWL)) and newer (bioelectrical impedance analysis (BIA) and scaled mass index (SMI)) condition indices to track seasonal cycles in three flatfishes — winter founder (Pseudopleuronectes americanus; three stocks), yellowtail flounder (Limanda ferruginea; three stocks), and summer flounder (Paralichthys dentatus; one stock) — with contrasting life histories in habitat, feeding, and reproduction. The %DWM and %DWL were good proxies for energy density (r2 > 0.96) and more strongly related to K, Kn, and SMI than to BIA metrics. Principal component analysis indicated many metrics performed similarly across species; some were confounded by size, sex, and maturity along PC1, while others effectively characterized condition along PC2. Stock differences were along PC1 in winter flounder, reflecting different sizes across stocks, whereas in yellowtail flounder differences occurred along PC2 related to condition. These comparisons, within and across species, highlight the broad applicability of some metrics and limitations in others. [ABSTRACT FROM AUTHOR]

Metamorphosis is a critical developmental stage that presents particular challenges in fish aquaculture. The sharp increase in mortality that accompanies this transformation has often been attributed to nutritional deficiencies. Providing live feed (the rotifer Brachionus plicatilis Müller, 1786 and the brine shrimp Artemiasalina (Linnaeus, 1758)) during the larval stages is costly and labour intensive, which explains why much effort has been put on early weaning. However, previous observations in winter flounder (Pseudopleuronectes americanus (Walbaum, 1792)) indicate that juveniles weaned after settlement had better survival than those weaned at the larval stage. In this study, we tested whether late weaning (at settlement (W0) and groups maintained on co-feeding for 1 month (W1), two months (W2), or 3 months (W3) after settlement) could improve juvenile survival and lipid composition. Our results demonstrated that maintaining co-feeding beyond the larval stage was essential for after-settlement survival. Juveniles co-fed until 90 days after settlement were 32.5% heavier. Analyses of fatty acid trophic markers suggested that juveniles preferentially fed on enriched rotifers rather than inert food. No pigmentation or fin erosion problems were observed in any of the weaning treatments, which indicates good rearing conditions. [ABSTRACT FROM AUTHOR]

Abstract Winter Flounder populations have declined throughout the southern New England/Mid-Atlantic (SNE/MA) region since the 1980s, and evidence suggests near extirpation of some local populations. Previous research has focused on the correlation between temperature and declining stock-productivity, supporting the hypothesis that a warming climate is a primary driver of the species decline. Our objective was to critically investigate several potential drivers of Winter Flounder's regional decline and collapse in the SNE/MA region by evaluating them in relation to management actions, spawning stock biomass (SSB), recruitment, productivity (PROD) and fishing mortality (F). Results indicate that the SNE/MA stock has remained below the 40% unfished biomass threshold (B 40%) since 1984, and that F was above the maximum sustainable fishing rate (F MSY) for most of the period between 1995 and 2010. We found a negative relationship between F and SSB between 1981 and 2000. Correlative analysis between young-of-the-year PROD and a number of biological and physical parameters resulted in 8 (out of 21) significant relationships. However, after correcting for multiple comparisons only two, the abundance of Striped Bass and Summer Flounder, remained significant. The PROD and recruitment analyses did not indicate strong environmental drivers and suggested recruitment compensation during the early 2000s in some surveys. In summary, we did not find evidence of a global environmental driver, such as temperature, explaining the decline of Winter Flounder. Rather, our analysis indicates that long-term overexploitation and failure of management to control harvest rates preceded and was likely a primary driver in the species decline and lack of recovery. Finally, following decades of overfishing, attempts to rebuild the Winter Flounder fishery likely will require a longer-term commitment than management has shown to date. Highlights • Winter Flounder populations have declined since the 1980’s: evidence suggests near extirpation of some local populations. • Our objective was to critically investigate several potential drivers of Winter Flounder’s regional decline and collapse. • We did not find evidence of a global environmental driver, such as temperature, explaining the decline of Winter Flounder. • Long-term overexploitation was likely a primary driver in the species’ decline and lack of recovery. [ABSTRACT FROM AUTHOR]

From 1996 to 2011, researchers observed Phoca vitulina concolor (Western Atlantic Harbor Seal) on regional overwintering grounds in the Great Bay–Mullica River estuary in southern New Jersey. Over this 15-y time series, 299 observations were completed, with maximum local abundance increasing from 100 individuals in 1996 to 160 individuals in 2011. Our study did not document the presence of Atlantic Harbor Seal pups. In addition, we analyzed 142 scat samples, resulting in 1419 sagittal fish otoliths recovered and identified. Dominant recovered otoliths were as follows: 48% Phycidae (Urophycis regia [Spotted Hake]/Urophycis chuss [Red Hake]; 25% Clupeidae (Clupea harengus [Atlantic Herring], Alosa sapidissima [American Shad], Brevoortia tyrannus [Atlantic Menhaden], A. pseudoharengus [Alewife], and A. aestivalis [Blueback Herring]); 13% Ammodytidae (Ammodytes americanus/A. dubius [sandlance]); 6% Pseudopleuronectes americanus (Winter Flounder); and 4% Scophthalmus aquosus (Windowpane Flounder). Average back-calculated prey lengths across all prey groups (min–max = 5–41 cm, average = 19.75 cm) indicated that Western Atlantic Harbor Seals might utilize both estuarine and ocean environments for foraging. This temperate estuary currently represents the southern limit of routine Western Atlantic Harbor Seal occupancy in the Northeast. As such, our results are valuable in monitoring future changes in habitat use potentially resulting from climate change. [ABSTRACT FROM AUTHOR]

Estuaries are impacted by multiple anthropogenic stressors from eutrophication to climate change. Long-term observational datasets allow the determination of trends in estuarine indicators and the prediction of future conditions. Here, a dataset of water quality and demersal fish community composition in a Long Island Sound embayment (Norwalk Harbor, Connecticut) from 1987 to 2016 was examined. Mean water column water temperature increased, dissolved oxygen decreased, and salinity increased over the study period, with simultaneous changes in the demersal fish community. Fish abundance declined overall, with declines in CPUE observed across multiple species including the commercially important winter flounder (Pseudopleuronectes americanus). As fish can serve as effective indicators of estuarine health, these changes suggest a negative shift in the health of this Long Island Sound embayment. Climate change presents an increasing threat to estuaries and the ecosystem services they provide, especially when coupled with other anthropogenic stressors. Management actions are needed at multiple spatial scales, from local to global, to combat these threats to estuarine health. [ABSTRACT FROM AUTHOR]

Winter flounder (Pseudopleuronectes americanus) is a benthic flatfish that is economically important for recreational and commercial fishing in North America. In the last twenty years, the species has undergone a drastic decline, mainly due to anthropic influence. The goal of this study was to gain knowledge on habitat preferences and behavior of juvenile winter flounder to improve the management of natural stocks and optimize release sites of juveniles produced for stock enhancement. Three abiotic factors (sediment, current, and salinity) potentially influencing the distribution of flatfish species were tested in a recircurlating flume with juvenile winter flounder. Time budgets of observed behaviors including swimming, orientation, and burying capacity were analyzed. Sediment texture was the only factor that significantly influenced the burying behavior of winter flounder juveniles; shear velocity, salinity, and sediment had no effect on the orientation of juveniles. [ABSTRACT FROM AUTHOR]

Decadal-scale climate variability and change can cause trends in oceanographic conditions that impact demographic rates. Rebuilding scenarios, therefore, developed assuming constant demographic rates may not be realistic. Winter flounder (Pseudopleuronectes americanus) is an important commercial and recreational species that has declined in the southern portion of its range despite reduced exploitation. Laboratory and mesocosm studies suggest that stock productivity is reduced under warmer conditions and that rebuilding to historical levels may not be possible. Our goal was to examine the rebuilding potential of winter flounder in the face of regional warming. We integrated winter temperature into a population model to estimate environmentally driven stock–recruitment parameters and projected the stock into the future under different climate and fishing scenarios. The inclusion of winter temperature had minor impacts on the estimates of current abundance, but provided greater understanding of the drivers of recruitment. Projections that included the environment suggest that rebuilding the stock to historical levels is unlikely. The integration of both fishing and the environment has the potential to provide more realistic expectations of future stock status. [ABSTRACT FROM AUTHOR]

We conducted experiments on the unidirectional freezing of solutions of winter flounder antifreeze protein or of a polypeptide which was based on twelve amino-acid residues of this protein. The temperature in the solutions and ice was measured with a small thermocouple. The interface temperature was defined as the temperature at the tip of the serrated or pectinate interface. The interface temperature of these solutions was lower than that of pure water. To vary this supercooling activity of these solutes, we preheated the solutions and cooled them before conducting identical experiments. It was found that short-time preheating caused further decreases in the interface temperature and interface velocities. Furthermore, the inclined interfaces and the narrow liquid regions inside the ice area became wider. To investigate the reasons for these changes, we measured aggregates of the solutes in the solutions. These aggregates were found to become larger as a result of preheating. Thus, it can be concluded that these large aggregates attenuated the ice growth by their interaction with ice. Finally, we carried out similar measurements by using pH-adjusted solutions of the protein to produce aggregates without preheating, and obtained similar supercooling enhancement by the aggregates. Thus, the effects of thermal denaturation on the supercooling were not significant in the preheating. [ABSTRACT FROM AUTHOR]

Nitrogen isotope ratios (δ 15 N) in juvenile winter flounder, Pseudopleuronectes americanus , were used to examine changes in nitrogen inputs to several Rhode Island, USA estuarine systems. Fish were collected over two three-year periods with a ten-year interval between sampling periods (2002–2004 and 2012–2014). During that interval numerous changes to nutrient management practices were initiated in the watersheds of these estuarine systems including the upgrade of several major wastewater treatment facilities that discharge to Narragansett Bay, which significantly reduced nitrogen inputs. Following these reductions, the δ 15 N values of flounder in several of the systems decreased as expected; however, isotope ratios in fish from upper Narragansett Bay significantly increased. We believe that low δ 15 N values measured in 2002–2004 were related to concentration-dependent fractionation at this location. Increased δ 15 N values measured between 2012 and 2014 may indicate reduced fractionation or that changes in wastewater treatment processes altered the nitrogen isotopic ratios of the effluents. [ABSTRACT FROM AUTHOR]

Age-0 winter flounder (Pseudopleuronectes americanus; 20- 90 mm in total length [TL]) and summer flounder (Paralichthys dentatus; 19-172 mm TL) were collected from the Seekonk and Taunton Rivers (in Rhode Island and Massachusetts, respectively) from May through September during 2009-2015, and stomach content analysis was used to assess diet composition and resource overlap for these species. Winter and summer flounder underwent ontogenetic dietary shifts. Winter flounder <40 mm TL predominantly fed on copepods, transitioning to amphipods, isopods, and bivalves with increasing size. Polychaetes also were consumed frequently by winter flounder, irrespective of size. The principal prey of summer flounder <60 mm TL were mysid shrimp and copepods, whereas sand shrimp (Crangon septemspinosa), amphipods, and fish were the dominant prey of larger conspecifics. There was minimal dietary overlap for the flounder species when comparisons were made independent of body size, indicating food niche segregation. For winter and summer flounder of equivalent sizes, however, dietary overlap was inversely related to TL. Moderate to high resource overlap occurred for small winter and summer flounder (<40 mm TL) and was attributed to their mutual reliance on copepods and amphipods. Despite evidence of dietary overlap, it is unlikely that shared prey resources were diminished enough to negatively affect either flounder species. [ABSTRACT FROM AUTHOR]

Bycatch is a constraint to the Atlantic sea scallop fishery, the most valuable single-species fishery along the eastern coast of the United States. To characterize trends in the bycatch of three flatfish species, a fishery-independent scallop dredge survey was conducted in two sea scallop access areas (Closed Areas I and II) on Georges Bank from 2011 to 2014. Generalized additive mixed models were used to identify seasonal bycatch hotspots of yellowtail, winter, and windowpane flounder. In all cases, spatially explicit models best fit the data (deviance explained: 47-73%) and provided insight into the spatial distribution underlying the seasonal trends in each area. Modeled catch rates for the three flatfish species suggested localized catches at discrete times of the year. Catches of yellowtail and windowpane flounder were highest in Closed Area II in the fall and winter, respectively. Winter flounder were caught in the highest numbers in Closed Area I during the summer and fall, and were largely absent from catches in Closed Area II. Our results suggest consistent seasonal trends that may help managers identify the optimal times to open the access areas to the scallop fleet in order to reduce flatfish bycatch. [ABSTRACT FROM AUTHOR]

This study evaluated the relative importance of the Narragansett Bay estuary (RI and MA, USA), and associated tidal rivers and coastal lagoons, as nurseries for juvenile winter flounder, Pseudopleuronectes americanus, and summer flounder, Paralichthys dentatus. Winter flounder (WF) and summer flounder (SF) abundance and growth were measured from May to October (2009-2013) and served as indicators for the use and quality of shallow-water habitats (water depth <1.5-3.0 m). These bioindicators were then analyzed with respect to physiochemical conditions to determine the mechanisms underlying intraspecific habitat selection. WF and SF abundances were greatest in late May and June (maximum monthly mean = 4.9 and 0.55 flounder/m for WF and SF, respectively) and were significantly higher in the tidal rivers relative to the bay and lagoons. Habitat-related patterns in WF and SF abundance were primarily governed by their preferences for oligohaline (0.1-5 ppt) and mesohaline (6-18 ppt) waters, but also their respective avoidance of hypoxic conditions (<4 mg DO/L) and warm water temperatures (>25 °C). Flounder habitat usage was also positively related to sediment organic content, which may be due to these substrates having sufficiently high prey densities. WF growth rates (mean = 0.25 ± 0.14 mm/day) were negatively correlated with the abundance of conspecifics, whereas SF growth (mean = 1.39 ± 0.46 mm/day) was positively related to temperature and salinity. Also, contrary to expectations, flounder occupied habitats that offered no ostensible advantage in intraspecific growth rates. WF and SF exposed to low salinities in certain rivers likely experienced increased osmoregulatory costs, thereby reducing energy for somatic growth. Low-salinity habitats, however, may benefit flounder by providing refugia from predation or reduced competition with other estuarine fishes and macroinvertebrates. Examining WF and SF abundance and growth across each species' broader geographic distribution revealed that southern New England habitats may constitute functionally significant nurseries. These results also indicated that juvenile SF have a geographic range extending further north than previously recognized. [ABSTRACT FROM AUTHOR]

Recently, several peptides have been studied regarding the defence process against pathogenic microorganisms, which are able to act against different targets, with the purpose of developing novel bioactive compounds. The present work focuses on the structural and functional evaluation of the palindromic antimicrobial peptide Pa -MAP2, designed based on the peptide Pa -MAP from Pleuronectes americanus . For a better structural understanding, molecular modelling analyses were carried out, together with molecular dynamics and circular dichroism, in different media. Antibacterial activity against Gram-negative and positive bacteria was evaluated, as well as cytotoxicity against human erythrocytes, RAW 264.7, Vero and L6 cells. In silico docking experiments, lipid vesicle studies, and atomic force microscopy (AFM) imaging were carried out to explore the activity of the peptide. In vivo studies on infected mice were also done. The palindromic primary sequence favoured an α-helix structure that was pH dependent, only present on alkaline environment, with dynamic N- and C-terminals that are stabilized in anionic media. Pa -MAP2 only showed activity against Gram-negative bacteria, with a MIC of 3.2 μM, and without any cytotoxic effect. In silico , lipid vesicles and AFM studies confirm the preference for anionic lipids (POPG, POPS, DPPE, DPPG and LPS), with the positively charged lysine residues being essential for the initial electrostatic interaction. In vivo studies showed that Pa -MAP2 increases to 100% the survival rate of mice infected with Escherichia coli . Data here reported indicated that palindromic Pa -MAP2 could be an alternative candidate for use in therapeutics against Gram-negative bacterial infections. [ABSTRACT FROM AUTHOR]

A typically α-helical antifreeze protein (wfl AFP-6) from winter flounder, Pseudopleuronectes americanus, forms amyloid fibrils during freezing. In this study, the effects of distinct components of the freezing process were examined. Freezing of wfl AFP-6 in the presence of template ice was shown to be necessary for rapid conversion to an amyloid conformation. Neither subfreezing temperature nor phase change was sufficient. Thus, specific interaction with the ice surface was essential. The ice-induced formation of amyloid appeared to be unique to this helical antifreeze, it required high concentrations of protein and it occurred over a range of pH values. These results define a method for rapid formation of amyloid by wfl AFP-6 on demand under physiological conditions. [ABSTRACT FROM AUTHOR]

In decapod crustaceans, arthropod steroid hormones or ecdysteroids regulate molting. These hormones are synthesized and released from a pair of molting glands called the Y-organs (YO). Cyclic nucleotide, mTOR, and TGFβ/Smad signaling pathways mediate molt cycle-dependent phase transitions in the YO. To further identify the genes involved in the regulation of molting, a YO transcriptome was generated from three biological replicates of intermolt blackback land crab, Gecarcinus lateralis . Illumina sequencing of cDNA libraries generated 227,811,829 100-base pair (bp) paired-end reads; following trimming, 90% of the reads were used for further analyses. The trimmed reads were assembled de novo using Trinity software to generate 288,673 contigs with a mean length of 872 bp and a median length of 1842 bp. Redundancy among contig sequences was reduced by CD-HIT-EST, and the output constituted the baseline transcriptome database. Using Bowtie2, 92% to 93% of the reads were mapped back to the transcriptome. Individual contigs were annotated using BLAST, HMMER, TMHMM, SignalP, and Trinotate, resulting in assignments of 20% of the contigs. Functional and pathway annotations were carried out via gene ontology (GO) and KEGG orthology (KO) analyses; 58% and 44% of the contigs with BLASTx hits were assigned to GO and KO terms, respectively. The gene expression profile was similar to a crayfish YO transcriptome database, and the relative abundance of each contig was highly correlated among the three G. lateralis replicates. Signal transduction pathway orthologs were well represented, including those in the mTOR, TGFβ, cyclic nucleotide, MAP kinase, calcium, VEGF, phosphatidylinositol, ErbB, Wnt, Hedgehog, Jak-STAT, and Notch pathways. [ABSTRACT FROM AUTHOR]

The effect of climate variability on flatfish includes not only the effects of warming on sensitive life history stages, but also impacts from more frequent or unseasonal extreme cold temperatures. Cold weather events can affect the overwintering capabilities of flatfish near their low temperature range limits. We examined the responses of two flatfish species, the thin-bodied windowpane ( Scophthalmus aquosus ) and cold-tolerant winter flounder ( Pseudopleuronectes americanus ), to variable winter temperatures in a Northwest Atlantic estuary using abundance and size data collected during a monitoring study, the Aquatic Biological Survey, conducted from 2002 to 2010. Winter and spring abundances of small (50 to 120 mm total length) juvenile windowpane were positively correlated with adult densities (spawning stock) and fall temperatures (thermal conditions experienced during post-settlement development for the fall-spawned cohort) of the previous year. Windowpane abundances in the estuary were significantly reduced and the smallest size class was nearly absent after several consecutive years with cold (minimum temperatures < 1 °C) winters. Interannual variation in winter flounder abundances was unrelated to the severity of winter temperatures. A Paulik diagram illustrates strong positive correlations between annual abundances of sequential winter flounder life history stages (egg, larval, Age-1 juvenile, and adult male) within the estuary, reflecting residency within the estuary through their first year of life. Temperature variables representing conditions during winter flounder larval and post-settlement development were not significant factors in multiple regression models exploring factors that affect juvenile abundances. Likewise, densities of predators known to consume winter flounder eggs and/or post-settlement juveniles were not significantly related to interannual variation in winter flounder juvenile abundances. Colder estuarine temperatures through the first year of life were associated with smaller Age-1 winter flounder body size. For example, Age-1 winter flounder developing under conditions that differed by 1.9 °C in mean daily water temperature, averaged 98.7 mm total length (TL) and 123.1 mm TL, for the relatively cold vs. moderate years, respectively. More frequent cold temperature extremes associated with climate variability may negatively impact the overwintering capabilities of some flatfish near their cold temperature range limits, whereas cold-tolerant species may experience reduced growth, which imparts the ecological challenges associated with smaller body size. [ABSTRACT FROM AUTHOR]

Stable carbon and nitrogen isotope ratios were measured in young-of-the-year (YOY) winter flounder, Pseudopleuronectes americanus , collected from several Rhode Island, USA estuarine systems. These included three coastal lagoons, an estuarine river and Narragansett Bay. The δ 13 C trends observed along transects in several systems showed isotopically depleted terrestrial signals in the upper reaches of the estuaries. Significant differences ( P < 0.05) in δ 15 N were observed among all estuarine systems and these differences correlated ( P < 0.01) with human population densities in the watersheds. Although Narragansett Bay has a strong north–south gradient in nutrient concentrations this trend was not reflected in flounder δ 15 N. The northernmost station with the highest nutrient concentrations unexpectedly had significantly lower δ 15 N values. Depleted δ 15 N values at this nutrient-rich station may indicate that concentration-dependent fractionation needs to be considered when using nitrogen isotope ratios in biota to monitor anthropogenic nitrogen inputs in systems with high nitrogen loadings. [ABSTRACT FROM AUTHOR]

Cationic antimicrobial peptides (CAPs) defend against pathogens and, in some cases, exhibit potent anticancer activities. We previously reported that the pleurocidin NRC-03 causes lysis of breast cancer and multiple myeloma cells. NRC-03 also reduces the EC 50 of other cytotoxic compounds and prevents tumor growth in vivo. However, the therapeutic utility of NRC-03 may be limited by its susceptibility to degradation by proteases. The goal of this study was to characterize the anticancer activities of a d -amino acid analog of NRC-03 ([D]-NRC-03) that was predicted to be resistant to proteolytic degradation. Unlike NRC-03, [D]-NRC-03 was not degraded by human serum or trypsin and, in comparison to NRC-03, showed increased killing of breast cancer cells, including multidrug-resistant cells; however, [D]-NRC-03 was somewhat more cytotoxic than NRC-03 for several types of normal cells. Importantly, [D]-NRC-03 was more effective than NRC-03 in vivo since 4-fold less peptide was required for an equivalent inhibitory effect on the growth of breast cancer cell xenografts in immune-deficient mice. These findings demonstrate that a d -amino acid analog of NRC-03 overcomes a major limitation to the therapeutic use of NRC-03, namely peptide stability. Further modification of [D]-NRC-03 is required to improve its selectivity for cancer cells. [ABSTRACT FROM AUTHOR]

We observed that paired winter flounder ( Pseudopleuronectes americanus) sagittae are not morphologically or chemically identical. Statistically significant ( p < 0.05) chemical asymmetry was detected between the sagittae in five of eight elements (with three other elements, Sr, I, and Sn not statistically different). The blind-side otolith exhibited higher mean concentrations of Ba, Mn, Mg, Cu, and Zn trace elements than the eyed-side otolith. These asymmetries may be due to blind-side otoliths absorbing higher concentrations of transitional elements, partly as a result of environmental heterogeneity caused by redox reactions emanating from the sediments. Metamorphic transformation and the subsequent shift to the benthos by fully formed fish may also account for element concentration levels that were significantly different between juveniles and both sub-adults and adults. Our results also suggest that chemical uptake in a pair of winter flounder sagittae is an asynchronous event, and that each otolith potentially records the chemical history of its environment independent of the other. The physiological pathway for entry into winter flounder otoliths is uncertain and warrants further testing. Overall, our results have implications for other flatfish genera as well, and demonstrate the need for standardization of methodology when conducting otolith chemistry on flatfishes. [ABSTRACT FROM AUTHOR]