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For many years, parasite ecologists have debated the relative importance of phylogeny and ecology as drivers of parasite community structure. Here, we address this issue using data on the metazoan ectoparasite communities of different flatfish species. Twenty species of flatfish were collected along the continental shelf of the Southern Gulf of Mexico and examined for ectoparasites. Eight flatfish species were parasitized by at least one ectoparasite species. In total, 326 ectoparasites, representing 11 species (4 monogeneans, 4 copepods, 1 isopod, 1 branchiurid, and 1 leech) were removed from 1622 hosts examined. The highest prevalence (37.5%) occurred in Bomolochus sp1 from Trinectes maculatus, while the lower (0.1%) for Argulus sp., Gnathia sp. and Trachellobdella lubrica from Cyclopsetta chittendeni. Changes in the ectoparasite community structure per host species and region were evaluated using a Permutational Multivariate Analysis of Variance and represented by a multidimensional scaling analysis. Significant differences in the parasite species composition among regions and hosts were detected, but no significant interaction between regions and hosts occurred. A multivariate pairwise t-test detected significant differences in the parasite infracommunities between the Yucatan Shelf and the other two regions; in addition, significant differences were detected between C. chittendeni and the Syacium species as well as between Ancylopsetta dilecta and Syacium papillosum. In this case, there is no relationship between the patterns of ectoparasitic community structure and the inherent phylogenetic affinity of the hosts; instead, the variations in ectoparasitic communities are determined by a regional ecological component. [ABSTRACT FROM AUTHOR]

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]

We investigated the gastric evacuation rate (GER) and maintenance ration (MR) for the adult pointhead flounder Cleisthenes pinetorum (77–421 g) at 4°C, 9°C, and 14°C which reflect the bottom, middle, and surface temperatures of their habitat in early summer. GERs were obtained from gravimetric experiments with 34 flounders fed juvenile walleye pollock Gadus chalcogrammus as prey. A 169‐day feeding experiment for 67 pointhead flounders fed krill Thysanoessa inermis was undertaken to measure MR. The effects of a 10°C temperature increase (Q10) on the GER and the MR were 6.55 and 2.04, respectively, indicating that the effect of temperature was greater on GER than on MR. As a result, the differences between the GER and MR, indicating the maximum amount of food ingestible for growth, were 2.8 and 30.7 cal·g−1 day−1 at 4 and 14°C, respectively. The water temperature on the sea floor generally remained at <4°C from winter through summer, but exceeded 10°C in the surface layer of Funka Bay, where pointhead flounders were sampled. Therefore, their growth rate should be considerably limited if they remain in the bottom layer. The unique ecology of this species among the flatfishes of floating from sea floor and feeding at pelagic zones may represent a strategy to compensate for the physiological limitation of growth at low temperatures. [ABSTRACT FROM AUTHOR]

Visual signals are involved in many fitness‐related tasks and are therefore essential for survival in many species. Aquatic organisms are ideal systems to study visual evolution, as the high diversity of spectral properties in aquatic environments generates great potential for adaptation to different light conditions. Flatfishes are an economically important group, with over 800 described species distributed globally, including halibut, flounder, sole, and turbot. The diversity of flatfish species and wide array of environments they occupy provides an excellent opportunity to understand how this variation translates to molecular adaptation of vision genes. Using models of molecular evolution, we investigated how the light environments inhabited by different flatfish lineages have shaped evolution in the rhodopsin gene, which is responsible for mediating dim‐light visual transduction. We found strong evidence for positive selection in rhodopsin, and this was correlated with both migratory behavior and several fundamental aspects of habitat, including depth and freshwater/marine evolutionary transitions. We also identified several mutations that likely affect the wavelength of peak absorbance of rhodopsin, and outline how these shifts in absorbance correlate with the response to the light spectrum present in different habitats. This is the first study of rhodopsin evolution in flatfishes that considers their extensive diversity, and our results highlight how ecologically‐driven molecular adaptation has occurred across this group in response to transitions to novel light environments. [ABSTRACT FROM AUTHOR]

The marbled flounder (Pseudopleuronectes yokohamae) is a demersal flatfish species, widely distributed in the northwestern Pacific region. In the present study, the mitochondrial DNA (mtDNA) control region was used to determine the genetic diversity and population genetic structure of this species. We obtained a 380 bp segment of the mtDNA control region after the alignment of 78 individual sequences from P. yokohamae collected from two locations in Korea (Biungdo and Mukho) and one location in Japan (Tohoku) and 103 individual sequences from a previous study (Yokjido and Namhae). The overall haplotype diversity and nucleotide diversity were 0.983 ± 0.003 and 0.016 ± 0.008, respectively. The genealogical relationships of the mtDNA control region did not exhibit any specific genealogical association according to sampling location. The pairwise FST value indicated that the Biungdo (west coast of Korea) and Tohoku (Japan) populations showed genetically differentiated structures (but the Tohoku and Mukho populations did not). However, there was no discernible difference between the Mukho population from Korea's eastern coast and the Yokjido and Namhae populations from the southern coast. The biological characteristics of P. yokohamae and oceanographic barriers may have contributed to producing genetically distinct populations. [ABSTRACT FROM AUTHOR]

Southern flounder skin pigmentation is a critical phenotypic characteristic for this species' survival in the natural environment. Normal pigmentation allows rapid changes of color for concealment to capture prey and UV light protection. In contrast, highly visible hypopigmented pseudo-albinos exhibit a compromised immune system and are vulnerable to predation, sensitive to UV exposure, and likely have poor survival in the wild. Skin and brain tissue samples from normally pigmented and hypopigmented individuals were analyzed with next-generation RNA sequencing. A total of 1,589,613 transcripts were used to identify 952,825 genes to assemble a de novo transcriptome, with 99.43% of genes mapped to the assembly. Differential gene expression and gene enrichment analysis of contrasting tissues and phenotypes revealed that pseudo-albino individuals appeared more susceptible to environmental stress, UV light exposure, hypoxia, and osmotic stress. The pseudo-albinos' restricted immune response showed upregulated genes linked to cancer development, signaling and response, skin tissue formation, regeneration, and healing. The data indicate that a modified skin collagen structure likely affects melanocyte differentiation and distribution, generating the pseudo-albino phenotype. In addition, the comparison of the brain transcriptome revealed changes in myelination and melanocyte stem cell activity, which may indicate modified brain function, reduced melanocyte migration, and impaired vision. [ABSTRACT FROM AUTHOR]

Ocean acidification could modify the bioavailability and chemical properties of trace elements in seawater, which could affect their incorporation into the calcareous structures of marine organisms. Fish otoliths, biomineralized ear stones made by aragonite, are suspended within the endolymph fluid of teleosts, indicating that the elemental incorporation of otoliths might also be susceptible to ocean acidification. In this study, we evaluated the combined effects of CO2‐induced ocean acidification (pH 8.10, 7.70, and 7.30, corresponding to ocean acidification scenarios under the representative concentration pathway 8.5 model as projected by the Intergovernmental Panel on Climate Change) and water elemental concentrations of strontium (Sr) and barium (Ba; low, medium, and high) on elemental incorporation into otoliths of the flounder Paralichthys olivaceus at early life stages. Our results revealed that the elemental incorporation of Sr and Ba into otoliths was principally dependent on the corresponding water elemental concentrations rather than on ocean acidification. Moreover, the partition coefficients (DMe) of Sr and Ba may stabilize after dynamic equilibrium is reached as the water elemental concentration increases, but are not affected by ocean acidification. Therefore, the incorporation of Sr and Ba into otoliths of the flounder at early life stages may not serve as an effective indicator of ocean acidification. In other words, the findings suggest that ocean acidification does not impact the incorporation of Sr and Ba incorporation into otoliths when tracing the temperature or salinity experiences of the flounder. Our findings will provide new knowledge for understanding the potential ecological effects of ocean acidification on the recruitment dynamics of fish species. [ABSTRACT FROM AUTHOR]

Southern flounder are an iconic coastal finfish through the Southeast U.S. Atlantic and Gulf of Mexico. Southern flounder spend the early part of their lives in coastal and estuarine habitats, later moving offshore to spawn. Several decades of research have provided much clarity to the biology, life history, and aquaculture aspects of southern flounder—this information is summarized and reviewed in this study. Despite substantial improvement in understanding the species, major questions remain about their recruitment, offshore behaviors, captive rearing, and management. Recently, southern flounder have also been in focus because of substantial synchronous population declines throughout their range with specific concerns that recruitment failure and possibly climate change may be implicated. Management of southern flounder has thus far taken place within individual states, but coming into focus is the possibility that larger coastwide management approaches may need to be considered due to both the migratory nature of the species and the possibility of population stressors acting at regional scales. Many states have already begun aquaculture and enhancement efforts, with an eye toward supplementing wild populations. Large group efforts, like the symposium that led to this study, will likely be needed to tackle the complex challenges confronting southern flounder. [ABSTRACT FROM AUTHOR]

Purpose. Rhabdoviruses are the most abundant and widespread fish pathogens. Viruses from five genera (Sprivivirus, Perhabdovirus, Siniperhavirus, Scophrhavirus and Novirhabdovirus) of the Rhabdoviridae family infect various fish species, including cyprinids (Cypriniformes), salmonids (Salmoniformes), percids (Perciformes), flatfishes (Pleuronectidae) and eels (Anguilliformes). In the list of particularly dangerous fish diseases of the World Organization for Animal Health (WOAH), rhabdoviruses have the most representatives, the control and monitoring of which is mandatory. Since fish rhabdoviruses are widespread in Europe, there is a potential threat for Ukrainian aquaculture, so the purpose of the review is to inform industry professionals (veterinarians, fish farmers, farm owners) about the biological risks and threats associated with this group of pathogens. Findings. The article presents data on certain fish rhabdoviruses that are not included in the WOAH list, but also pose a potential threat to freshwater aquaculture. The characteristics of rhabdoviruses infecting pike (Esox lucius), European eel (Anguilla anguilla), brown trout (Salmo trutta), perch (Perca fluviatilis) and pikeperch (Stizostedion lucioperca) are briefly described. The obvious signs of diseases caused by fish perabdoviruses and spiriviruses have been characterized, and methods of their diagnosis have been indicated. Attention is focused on such methods of virus identification as the cell culture, enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR). Data on the spread of perhabdoviruses in Europe and methods of their prevention in farms are given. Practical Value. Monitoring of rhabdoviruses in fish farming enterprises of Ukraine will allow determining the ecological niches of these pathogens and to identify the potential risks of epizootics both in aquaculture and in natural populations of sensitive hosts. The study of the molecular biological properties of these viruses will contribute to the improvement of their diagnostics. [ABSTRACT FROM AUTHOR]

Inclusion effect of different amount of jack mackerel meal (JMM) in the diets substituting 50% fish meal (FM) with corn gluten meal (CGM) on growth, feed availability, biochemical composition, plasma, and serum chemistry of olive flounder (Paralichthys olivaceus) was elucidated. Seven experimental diets were formulated. The control (Con) diet contained 60% FM. Fifty percent of FM in the Con diet was substituted with CGM, and then 5, 10, 20, 30, 40, and 50% JMM were added at the expense of FM to formulate the CJ5, CJ10, CJ20, CJ30, CJ40, and CJ50 diets, respectively. All formulated feeds were assigned to triplicate groups of fish. A total of 420 juvenile fish averaging 18 ± 0.01 g (mean ± SEM) was uniformly divided into 21, 50-L tanks, with 20 fish per tank. Fish were carefully hand-fed to satiation for 8 weeks. The weight gain of olive flounder fed the Con diet was significantly (p < 0.001) higher than that of fish fed the CJ5, CJ10, and CJ20 diets, but not significantly (p > 0.05) different from that of fish fed the CJ30, CJ40, and CJ50 diets. Olive flounder fed the Con diet achieved significantly (p < 0.001 and p < 0.04) greater specific growth rates (SGR) and feed consumption than those of fish fed the CJ5 and CJ10 diets, but not significantly (p > 0.05) different from those of fish fed the CJ20, CJ30, CJ40, and CJ50 diets. However, there were no significant (p > 0.05) differences in feed utilization, proximate composition, amino acid profiles, and plasma and serum parameters of olive flounder. In conclusion, incorporation of 30, and 20% JMM are the most desirable treatments in the olive flounder diets replacing 50% FM with CGM based on weight gain, and SGR and feed consumption, respectively. This study will be very helpful to develop low-FM diets for sustainable olive flounder culture. [ABSTRACT FROM AUTHOR]

Japanese flounder Paralichthys olivaceus is one of the most valuable coastal flatfish species in East Asia. To investigate post‐settlement growth and mortality, juveniles were sampled in Tango Bay (Japan) weekly throughout the settlement period in 2007 and 2008. Otolith (lapillus) microstructure analysis enabled the categorization of juveniles into six biweekly cohorts each year. Later cohorts exhibited higher growth rates possibly because of higher water temperatures. A key observation was the direct relationship between high mortality and high density in mid‐season cohorts in both years, pointing to density‐dependent mortality. This increased mortality may be attributed to predation, including cannibalism by earlier cohorts. Furthermore, growth‐selective mortality was evident soon after settlement, underscoring the vulnerability of slow growers to predation during the early juvenile stage. Although earlier and later cohorts were less abundant but showed promising recruitment potential, the prospective contribution of mid‐season cohorts to the adult population remained uncertain. The results clearly highlight the importance of density‐dependent mortality in population regulation in post‐settlement Japanese flounder. [ABSTRACT FROM AUTHOR]

Simple Summary: The welfare of farmed fish is crucial in aquaculture, requiring demanding attention to ensure their health and safety throughout the farming process. Stress and pain experienced by fish have profound implications for their overall well-being, highlighting the importance of mitigating these factors. Enhancing fish welfare promotes the sustainability of aquaculture and fortifies fish resilience against stressors. Despite significant advancements in production and species diversity in Korean aquaculture, the welfare of farmed fish remains largely neglected. To address potential welfare issues in the farming process, we conducted an analysis focusing on olive flounder, a staple species in Korean aquaculture. We identified welfare concerns relevant to olive flounder farming, laying the foundation for the development of robust welfare standards and the promotion of ethical and responsible practices in Korean aquaculture. Korean aquaculture has expanded considerably in recent decades; however, this growth has often prioritized quantity over fish welfare. Therefore, we analyzed the aquaculture practices of olive flounder, the predominant species in Korean consumption and production, within the framework of fish welfare. We conducted extensive interviews and surveys across olive flounder farms in Jeju-do and Wando to examine prevalent issues impacting fish welfare in aquaculture. These issues include stressors, mass mortality events, and disease outbreaks, all of which strain the welfare of farmed fish. Moreover, our survey revealed farmers' varying perceptions of fish welfare, highlighting the necessity for a cohesive approach. Accordingly, we propose recommendations to enhance fish welfare and establish a more sustainable aquaculture model in Korea. Ensuring fish welfare in aquaculture operations requires a comprehensive approach that considers the physiological and behavioral needs of fish throughout the farming lifecycle. By prioritizing fish welfare, Korean aquaculture can strengthen its growth while maintaining ethical standards and ensuring the well-being of farmed fish. This welfare-centric approach is crucial for the long-term sustainability and resilience of the Korean aquaculture industry. By addressing welfare concerns and promoting responsible practices, Korean aquaculture can foster an ethically sound and sustainable future. [ABSTRACT FROM AUTHOR]

Neutrophils represent an important asset of innate immunity. Neutrophils express myeloperoxidase (MPO) which is a heme-containing peroxidase involved in microbial killing. In this study, by using real-time quantitative PCR and Western blot analysis, the flounder MPO (Po MPO) was observed to be highly expressed in the head kidney, followed by spleen, gill, and intestine during ontogeny – during developmental stages from larvae to adults. Furthermore, Po MPO positive cells were present in major immune organs of flounder at all developmental stages, and the number of neutrophils was generally higher as the fish grew to a juvenile stage. In addition, flow cytometry analysis revealed that the proportion of Po MPO positive cells relative to leukocytes, in the peritoneal cavity, head kidney, and peripheral blood of flounder juvenile stage was 18.3 %, 34.8 %, and 6.0 %, respectively, which is similar to the adult stage in flounder as previously reported. The presence and tissue distribution of Po MPO during ontogeny suggests that Po MPO positive cells are indeed a player of the innate immunity at all developmental stages of flounder. • MPO transcripts and protein were first detected at 1-day post-hatch in flounder. • MPO was widely expressed in the immune related organs. • MPO+ cells exist in all developmental stages and increase in number as flounder grow. [ABSTRACT FROM AUTHOR]

Understanding consumer choice behavior for seafood is important for the efficient and sustainable use of marine resources and the improvement of human health. This study aims to identify the information content that effectively motivates Japanese consumers to purchase fresh fish products. Group interviews with 12 consumers were conducted in September 2021 to collect qualitative information on consumer evaluations of the presentation of package labels for freshness, taste, and serving suggestion. Subsequently, data were collected through a web-based survey, administered to 3651 consumers in the Kanto area, Japan from October to November 2021. A latent class logit model was applied to the data to estimate the influence of product attributes and personal characteristics on the choice and willingness-to-pay for each product attribute. The consumers gave the highest rating to freshness labels. The taste label was evaluated highly by consumers in one class. The group interview showed that when the serving suggestion label recommending meunière use was presented, consumers associated it with the recommendation to heat the fish because of less freshness. The results of the choice experiment also showed that the "meunière" label was evaluated negatively. The consumer segment characterized by a high income and frequent purchases of fish tended to respond to all types of labels. [ABSTRACT FROM AUTHOR]

Japanese flounder Paralichthys olivaceus is one of the most important coastal fish species in Japan. However, its catch in the southwestern Sea of Japan has been decreasing. Therefore, there is a need to improve the accuracy of stock assessment. Catch-at-age, which is the basis for stock assessment, is calculated based on the length–frequency distribution using age-length keys. It is recommended that this basic information is revised annually. However, the information for this species has not been updated for a relatively long period. In this study, growth curves were estimated and compared with those recorded from other areas. A multinomial logistic age-length key was generated and compared with the classical catch-at-age calculation method to examine potential errors. On the basis of the results obtained, a sex-specific von Bertalanffy growth curve was selected using the Bayesian information criterion. A model of sex and season was chosen for the multinomial logistic age-length key. The relative error was smaller and the estimated age composition was more accurate with the multinomial logistic age-length key, even when data with missing values were used. The improved accuracy of catch-at-age achieved due to the superior characteristics of the multinomial logistic age-length key is expected to be useful for the advancement of stock assessment. [ABSTRACT FROM AUTHOR]

The Southern Flounder is a marine flatfish occurring throughout neritic zones of the northwest Atlantic and is the target of important commercial and recreational fisheries throughout its range. Recent work in the Gulf of Mexico demonstrated that the timing of hatch in this species may impact the survival of larvae, with increased survival in individuals that hatch early, ostensibly exposing them to cooler temperatures in early development in warmer years. However, hatch timing is influenced by the timing of spawning, which itself is associated with adult offshore migrations that are driven by fall and winter cold fronts. We assessed whether increasing fall temperatures in estuarine systems where Southern Flounder reside might be impacting the timing of spawning migrations. We used a machine learning approach to elicit the impact of temperature and other factors on estuarine catch in fishery-independent samples during the spawning season. Key findings of this work were as follows: (1) mean fall water temperatures in estuaries of the northwestern Gulf of Mexico have risen steadily since 1980 in accordance with broader oceanic trends, and (2) annual Southern Flounder migratory activity has shifted towards later Julian calendar dates. Temperature was an important seasonal environmental cue and is likely a key driver of spawning migrations, confirming findings from previous studies. A later shift in spawning phenology is at odds with the timing of the "survival window" for larval Southern Flounder, and this uncoupling of ideal spawning versus hatch timing could be a contributing factor to observed population declines across the range of the species. [ABSTRACT FROM AUTHOR]

Simple Summary: As fish meal (FM) has become an unsustainable natural resource in fish feeds because of its plateaued production and increased price, looking for a substitute for FM is a tremendous concern for scientists. Meat meal (MM) and chicken by-product meal (CBM) are known as suitable replacers for FM in the olive flounder (P. olivaceus) feeds. The combined proteins can substitute for more FM than each of the respective protein sources in diets because the former can compensate for their nutritional deficiency or imbalance. However, FM substitution with an alternative source in fish feeds may influence the immunity of fish. Therefore, this study evaluated the FM replacement effect of the combined MM and CBM (CMC) in the olive flounder feeds on growth, feed availability, and disease resistance against S. iniae. The results of this study indicated that FM up to 60% (39% FM protein in the diet) could be replaceable with CMC in the 65% FM-based diets of olive flounder without causing an unfavorable effect on growth performance, feed availability, or survival of fish after S. iniae infection. This study aims to reveal the substitution impact of fish meal (FM) with the combined meat meal and chicken by-product meal (CMC) in the olive flounder (P. olivaceus) feeds on growth and feed availability. Seven experimental feeds were formulated. The control (CMC0) diet included 65% FM. In the CMC0 diet, the various (10%, 20%, 40%, 60%, 80%, and 100%) levels of FM were replaced with CMC, named as the CMC10, CMC20, CMC40, CMC60, CMC80, and CMC100 diets, respectively. The total number of 525 juvenile fish (9.2 ± 0.01 g; mean ± SD) was placed into 21 50-L flow-through tanks (25 juveniles/tank) with three replicates. Fish were hand-fed to apparent satiation for 8 weeks. After the 8-week feeding experiment, olive flounder fed the CMC10 (40.0 ± 0.60 g/fish, 2.99 ± 0.021%/day, and 39.57 ± 0.542 g/fish; mean ± SD), CMC20 (47.3 ± 2.58 g/fish, 3.24 ± 0.082%/day, and 45.16 ± 0.760 g/fish), and CMC40 (40.2 ± 1.17 g/fish, 3.00 ± 0.040%/day, and 39.43 ± 0.930 g/fish) diets attained superior (p < 0.0001 for all) weight gain, specific growth rate (SGR), and feed consumption compared to olive flounder fed the CMC0 (35.1 ± 0.96 g/fish, 2.81 ± 0.039%/day, and 33.75 ± 0.544 g/fish), CMC60 (31.7 ± 1.62 g/fish, 2.66 ± 0.068%/day, and 31.60 ± 1.080 g/fish), CMC80 (24.7 ± 0.63 g/fish, 2.33 ± 0.033%/day, and 25.27 ± 0.689 g/fish), and CMC100 (17.8 ± 0.32 g/fish, 1.92 ± 0.021%/day, and 18.99 ± 0.592 g/fish, respectively) diets. Weight gain, SGR, and feed consumption of olive flounder fed the CMC60 diet were comparable to olive flounder fed the CMC0 diet. Feed efficiency and protein efficiency ratio of olive flounder fed the CMC60 diet (1.02 ± 0.007 and 1.79 ± 0.034) were comparable to fish fed the CMC0 diet (1.04 ± 0.012 and 1.85 ± 0.021, respectively). None of the plasma and serum measurements, proximate composition, amino acid profiles, or survival of olive flounder after S. iniae infection were influenced by dietary treatments. In conclusion, CMC can substitute FM up to 60% (39% FM protein in the diet) without deteriorating growth performance, feed availability, or the survival of fish after S. iniae infection. [ABSTRACT FROM AUTHOR]

A new branchial fish parasitic cymothoid species, Elthusa phoenixsp. nov. (Crustacea: Isopoda: Cymothoidae), is described based on the ovigerous female collected from off Sohachi flounder, Cleisthenes pinetorum Jordan and Starks, 1904 obtained from Sado Island, Japan. Elthusa phoenixsp. nov. can be distinguished from all congeners by the following combination of features: body slightly twisted, elongated, dorsal surfaces smooth, 1.9 times as long as greatest width; pleon short, ∼11% body length, pleon 0.75 times as wide as pereon maximum width; cephalon symmetrical, sub-triangular 1.20 times wider than long, anterior margin rounded, turned down to form a rostrum; short uropods extending to middle of the pleotelson; pereopods 4–7 basis proximo-lateral margin with small carinate lobe; prominent fleshy lobes present on sternite of pereonite 7; antenna with 12 articles; maxilliped with oostegite lobes, and lateral margin with many plumose setae. [ABSTRACT FROM AUTHOR]

Objective: We investigate the interacting effects of fishery selectivity and sexual dimorphism by using the fisheries for Southern Flounder Paralichthys lethostigma and Summer Flounder P. dentatus as case studies. In both species, females are larger than males, and temperature‐sensitive sex determination can lead to an increased proportion of males at sexual differentiation in warmer temperatures. Methods: We developed a size‐, age‐, and sex‐structured population dynamics model for each species to understand how temperature‐induced sex reversal will interact with harvesting to impact population productivity. We considered scenarios with realistic sex ratios and varying levels of fishing pressure. Result: Our models of these species show that population egg production, abundance, biomass, and catch will all be constrained if sex ratios at differentiation become more male‐biased. For both species, climate‐induced changes to the sex ratio in early‐life stages could have a greater impact on relative catch than fishing mortality. We demonstrate that the spawning potential ratio may not be sensitive to climate‐induced changes in the sex ratio unless we account for changes in the sex ratio at differentiation in the historic baseline reproductive potential. Conclusion: These findings underscore the importance of utilizing sex‐specific stock assessments for species with temperature‐sensitive sex determination mechanisms. Impact statementIf climate change is inducing sex reversal in the wild populations of these two flounder species, it could have major impacts on fishery productivity. [ABSTRACT FROM AUTHOR]

Black flounder (Paralichthys orbignyanus, Pleuronectiformes) is a commercially significant marine fish with promising aquaculture potential in Argentina. Despite extensive studies on Black flounder aquaculture, its limited genetic information available hampers the crucial role genetics plays in the development of this activity. In this study, we first employed Illumina sequencing technology to sequence the entire genome of Black flounder. Utilizing two independent libraries—one from a female and another from a male—with 150 bp paired-end reads, a mean insert length of 350 bp, and over 35 X-fold coverage, we achieved assemblies resulting in a genome size of ~ 538 Mbp. Analysis of the assemblies revealed that more than 98% of the core genes were present, with more than 78% of them having more than 50% coverage. This indicates a somehow complete and accurate genome at the coding sequence level. This genome contains 25,231 protein-coding genes, 445 tRNAs, 3 rRNAs, and more than 1,500 non-coding RNAs of other types. Black flounder, along with pufferfishes, seahorses, pipefishes, and anabantid fish, displays a smaller genome compared to most other teleost groups. In vertebrates, the number of transposable elements (TEs) is often correlated with genome size. However, it remains unclear whether the sizes of introns and exons also play a role in determining genome size. Hence, to elucidate the potential factors contributing to this reduced genome size, we conducted a comparative genomic analysis between Black flounder and other teleost orders to determine if the small genomic size could be explained by repetitive elements or gene features, including the whole genome genes and introns sizes. We show that the smaller genome size of flounders can be attributed to several factors, including changes in the number of repetitive elements, and decreased gene size, particularly due to lower amount of very large and small introns. Thus, these components appear to be involved in the genome reduction in Black flounder. Despite these insights, the full implications and potential benefits of genome reduction in Black flounder for reproduction and aquaculture remain incompletely understood, necessitating further research. [ABSTRACT FROM AUTHOR]

Pleuronectiformes are flatfishes with high commercial value and a prominent example of successful marine adaptation through chromosomal evolution. Hence, the aim of this study was to analyze the 14 relative abundance of repetitive elements (satellite DNA and transposable elements (TE)) in the 15 genome of 10 fish species (8 flatfish) delving into the study of the species of special relevance, 16 Senegalese sole, Solea senegalensis. The results showed differences in the abundance of repetitive elements, with S. senegalensis exhibiting the highest frequency and coverage of these elements reaching the 40% of the genome and not at random distribution. It is noteworthy the presence of relevant peaks of Helitrons in centromeric/pericentromeric positions mainly in the bi-armed chromosomes 1, 2, 4, 6, 7, and 9. The position of the centromeres of this species determined through the genomic localization of the family of satellite DNA PvuII, and other repetitive sequences was obtained de novo. This allowed us to know the genomic position of the centromeres in 19 out of the 21 chromosomes of S. senegalensis. Helitrons showed an accumulation of tandem copies mainly in the pericentromeric positions of chromosomes 1 and 2, occupying a region, in the first case, of 600Kb of tandem repeats. That has only been previously described inmammals andplants.Divergence and copy number studies indicated the presence of active families in the species' genome and the existence of two important events of transposon activity (burst) in the genome of S. senegalensis, mainly accentuated in Helitrons. The results showed that only the families of DNA transposons exhibited a landscape with symmetrical bell-shaped distribution. The phylogenetic analysis of Helitron families revealed the presence of two large groups of families and the presence of four groups of sequences with heterogeneous distribution among chromosomes. Finally, the phylogenomic analysis of 8615 sequences belonging to Helitron insertions from 5 families of flatfish and two external species, allowed to classify the copies into nine groups of sequences with different levels of divergence and clusters, including some branches with distant phylogenetically species. The implications of this study will help to expand the knowledge of chromosome structure and evolution of these species. [ABSTRACT FROM AUTHOR]

To understand the relationship between the radioactive cesium (Cs) concentration in muscle of Japanese flounder Paralichthys olivaceus and the species' biological characteristics (size, sex, and age) under conditions of ecological equilibrium (i.e., distributed among ecosystem components over sufficient time, and with nearly constant ratios of Cs concentration in organisms to the concentration in water) as existed before the accident at the Fukushima Dai‐ichi Nuclear Power Station (FDNPS), Japan, in 2011, we examined stable Cs, as it is thought to exist in equilibrium in the environment and behave similarly to radioactive Cs in aquatic animals. The concentration of stable Cs in 241 P. olivaceus (range 216–782 mm total length [TL]) collected in Sendai Bay, approximately 90 km north of the FDNPS, in June–July 2015 was expressed as an exponential function with size as an independent variable; the results show the concentration of stable Cs doubled with an increase in TL of 442 mm. Next, to evaluate the cause of the size‐dependent change in stable Cs concentration, we examined 909 individuals (200–770 mm TL) collected in September 2013–July 2015 to determine their feeding habit based on size. Analysis of the frequency of occurrence of prey organisms in stomach contents showed that sand lance Ammodytes japonicus (55–180 mm standard length [SL]) was the most consistently consumed across size classes. Analysis on a wet‐mass basis showed that A. japonicus and anchovy Engraulis japonicus (65–130 mm SL) were the main food of P. olivaceus sized 200–599 mm TL, whereas chub mackerel Scomber japonicus (120–230 mm SL) and two species of flatfishes (180–205 mm SL) were abundant in the diet of P. olivaceus sized ≥600 mm TL. All these prey items were presumed to have similar concentrations of stable Cs. Based on the above, the effect of diet on the relationship between stable Cs in muscle and fish size was considered negligible. That the diet of P. olivaceus largely did not change with size was also confirmed by C and N stable isotope ratios in P. olivaceus and their prey species. Therefore, the Cs–size relationship is probably determined by changes in the balance between the rate of Cs intake from food and seawater and the excretion rate during growth, both of which change as functions of body mass. Values of stable Cs concentrations among environmental components and animals appear to be a valid indicator for understanding the radioactive Cs distribution in the marine environment and aquatic animals under the equilibrium state, as existed before the 2011 nuclear accident. [ABSTRACT FROM AUTHOR]

Flatfish undergo a remarkable metamorphosis from symmetrical pelagic larvae to fully asymmetrical benthic juveniles. The most distinctive features of this transformation is the migration of one eye. The molecular role of thyroid hormone in the metamorphosis process in flatfishes is well established. However, the regulatory network that facilitates eye movement remains enigmatic. This paper presents a morphological investigation of the metamorphic process in turbot eyes, using advanced imaging techniques and a global view of gene expression. The study covers migrant and non-migrant eyes and aims to identify the genes that are active during ocular migration. Our transcriptomic analysis shows a significant up-regulation of immune-related genes. The analysis of eye-specific genes reveals distinct patterns during the metamorphic process. Myosin is highlighted in the non-migrant eye, while ependymin is highlighted in the migrant eye, possibly involved in optic nerve regeneration. Furthermore, a potential association between the alx3 gene and cranial restructuring has been identified. Additionally, it confirmed simultaneous adaptation to low light in both eyes, as described by changes in opsins expression during the metamorphic process. The study also revealed that ocular migration activates systems asynchronously in both eyes, providing insight into multifaceted reorganization processes during metamorphosis of flatfish. Flatfish eye migration in metamorphosis study shows up-regulated immune genes. The process involves roles of myosin/ependymin, the link of alx3's to cranial restructuring, changes in opsins adaptation to low light and an asynchronous system activation. [ABSTRACT FROM AUTHOR]

Trypanorhynch cestode larvae were found parasitizing specimens of dusky flounder Syacium papillosum (Linnaeus, 1758) in the Southeastern Gulf of Mexico (s-GoM). Plerocercoids were recovered from a total of 194 flatfish, embedded in the intestine and stomach wall. Trypanorhynch were identified using morphology and a molecular phylogeny using newly sequenced partial 28S (region D1-D3) ribosomal DNA in combination with data derived from other species of trypanorhynchs available from GenBank. Larvae representing three genera of trypanorhynch cestodes, Nybelinia Poche, 1926; KotorellaEuzet & Radujkovic, 1989 and Oncomegas Dollfus, 1929 were found in dusky flounder specimens in the s-GoM. These plerocercoids represent six species: Nybelinia sp. 1, Nybelinia sp. 2, Nybelinia sp. 3, Nybelinia sp. 4, Kotorella pronosoma (Stossich, 1901) and Oncomegas wageneri (Linton, 1890) Dollfus, 1929. All cestode specimens in this study represent new locality records for their respective species. [ABSTRACT FROM AUTHOR]

Background. Reversed condition is rarely found in most flatfishes in natural environment, except for some certain species. The mechanism controlling the reversals in flatfishes has been studied in some cultivated species, whereas some have only few cases for the entire family and remain unclear. Here, we report the first record of a dextral (reversed) specimen of Parabothus taiwanensis Amaoka & Shen, 1993 collected off southwestern Taiwan recently. It represents the second reversed case ever recorded in Bothidae. We aim to provide a detailed description of this dextral specimen and compared to the sinistral (normal) specimens collected from the vicinity. Methods. Specimens were fixed in 4% formaldehyde and transferred to 70% ethanol for preservation. Meristic and morphometric characters were examined for both dextral and sinistral specimens. Dissections were made on specimens to confirm the position of internal organs. Lastly, X-radiographs were taken to elucidate the osteological features. Results. As a result, no differences of both meristic and morphometric characters were observed between the dextral and sinistral specimens. Nevertheless, situs inversus viscerum is discovered in the dextral specimen for the first time in Bothidae and the sixth record within flatfishes. [ABSTRACT FROM AUTHOR]

Background: Salinomycin, an antibiotic, have potential as a veterinary drug for fish due to its anti-parasitic activity against several fish parasites. Thus the residual levels of salinomycin in muscles of two significant aquaculture species in Korea, olive flounder and black rockfish, were analyzed using HPLC-MS-MS. Results: The proper method to analyze the residual salinomycin in fish muscles using LC-MS-MS was settled and the method was validated according to CODEX guidelines. The residues in three distinct groups for two fish species were analyzed using the matrix match calibration curves at points of five different times following oral administration. After oral administration, salinomycin rapidly breaks down in both olive flounder and black rockfish. After 7th days, the average residue in all groups of two fish spp. decreased below limit of quantitation (LOQ). Conclusion: Due to low residue levels in fish muscles, salinomycin may therefore be a treatment that is safe for both fish and humans. This result could contribute to establishment of MRL (minimal residual limit) for approval of salinomycin for use in aquaculture. [ABSTRACT FROM AUTHOR]

Integrative studies are lacking on the responses of digestive enzymes and energy reserves in conjunction with morphological traits at distinct postprandial times in marine estuarine‐dependent flatfishes of ecological and economic importance, such as Paralichthys orbignyanus. We determined total weight (TW), hepato‐somatic index (IH), activities of digestive enzymes in the intestine, and the concentration of energy reserves in the liver and the muscle at 0, 24, 72, and 360 h after feeding in juveniles of P. orbignyanus. Amylase activity decreased at 72 h (about 30%). Maltase, sucrose, and lipase activities reached peak at 24 h (67%, 600%, and 35%, respectively). Trypsin and aminopeptidase‐N activities at 24 and 72 h, respectively, were lower than those at t = 0 (53% and 30%). A peak increase in the concentration of glycogen and triglycerides in the liver (24 h) (86% and 89%, respectively) occurred. In muscle, glycogen and triglyceride concentrations were unchanged at 24 h and higher at 72 and 360 h (100% and 60%). No changes were found in TW, IH, free glucose in the liver and muscle, and protein in the liver. The protein concentration in the muscle sharply increased at 24 and 360 h after feeding (60%). The results indicate a distinct and specific response of central components of carbohydrate, lipid, and protein metabolism that could be adjustments at the biochemical level upon periods of irregular feeding and even of long‐term food deprivation inside coastal lagoons or estuaries. The distinct responses of digestive enzymes in the intestine and energy reserves in the liver and muscle suggest the differential modulation of tissue‐specific anabolic and catabolic pathways that would allow the maintenance of physical conditions. [ABSTRACT FROM AUTHOR]

Measurement of target strength (TS) is important for estimating the abundance of species using fisheries acoustics. However, most researchers have only used a limited number of representative frequencies for acoustic measurements of fish without a swim bladder (bladderless fish). Here, we measured the broadband TS of three bladderless fish species, arabesque greenling (Pleurogrammus azonus), Pacific sand lance (Ammodytes personatus), and pointhead flounder (Cleisthenes pinetorum), using two broadband echosounders. TS measurements were conducted in a seawater tank over frequency ranges of 45–90 and 80–120 kHz using a tether method. Higher TS and directivity were observed at higher frequencies than at lower frequencies for pointhead flounder and arabesque greenling. However, the TS for Pacific sand lance was relatively flat over the measured frequency spectra. Additionally, the TS of pointhead flounder and Pacific sand lance could be expressed as a function of body length and the TS of arabesque greenling could be expressed as a function of body length and frequency, which could be used in fish species discriminations and size estimations. [ABSTRACT FROM AUTHOR]

Biacanthus pleuronichthydis (Yamaguti, 1939) is redescribed based on specimens of the female, recovered from the body surface of the bastard halibut, Paralichthys olivaceus (Temminck & Schlegel, 1846) (Pleuronectiformes, Paralichthyidae), which is a new host for the species. [ABSTRACT FROM AUTHOR]

Simple Summary: With the aggravation of water eutrophication and global climate change, macroalgal blooms along coastal areas worldwide have become increasingly common in recent years. As the largest green macroalgal bloom, in the Yellow Sea of China we can observe that environmental stress caused by the overgrowth and degradation of Ulva prolifera has a harmful effect on marine organisms and the aquaculture industry. Therefore, exploring the harmful effect of Ulva prolifera stress on fish could promote the development of aquaculture in the Yellow Sea. This study revealed that Ulva prolifera stress suppressed antioxidant capacity in the liver and induced an inflammatory response accompanied by the activation of endoplasmic reticulum stress in the head kidney of the Japanese flounder, which could lead to huge damage to fish health. As the largest green macroalgal bloom in the Yellow Sea of China, the overgrowth and degradation of Ulva prolifera (U. prolifera) have a harmful effect on marine organisms and the aquaculture industry. However, the regulation mechanism of U. prolifera stress on the antioxidant capacity and inflammatory response of marine fish is still not completely understood. A 15-day exposure experiment was conducted to evaluate the effects of U. prolifera stress on the antioxidant capacity and inflammatory response of the Japanese flounder (Paralichthys olivaceus) (283.11 ± 6.45 g). The results showed that U. prolifera stress significantly decreased their survival rate. Serum total antioxidant capacity (T-AOC) and non-specific immune-related enzyme activities were significantly impacted under U. prolifera conditions. Moreover, U. prolifera stress significantly decreased T-AOC, superoxide dismutase (SOD) activity, and catalase (CAT) activities in the liver, while malondialdehyde (MDA) contents were significantly increased. Similarly, antioxidant-related gene (cat, nrf2, and keap1) expressions were synchronously downregulated in the liver under U. prolifera stress. Furthermore, U. prolifera stress significantly upregulated pro-inflammatory gene (tnf-α, il-1β, ifn-γ, and p65) expressions and the phosphorylation levels of the p38 and JNK MAPK pathways in the head kidney. In addition, endoplasmic reticulum (ER) stress-related gene and protein expressions were also upregulated in the head kidney. Overall, these results revealed that U. prolifera stress suppressed the antioxidant capacity and induced an inflammatory response in the Japanese flounder. This study could advance the understanding of the adverse effects of U. prolifera stress on marine benthic fish and promote the sustainable development of aquaculture. [ABSTRACT FROM AUTHOR]

The isoflavones genistein and daidzein are flavonoid compounds mainly found in legumes, especially in soybeans and their derived products. These flavonoids can be present in agricultural, domestic and industrial wastewater effluents as a result of anthropogenic activities and may be discharged in the environment. Due to the large growth of the aquaculture sector in recent decades, new and cost‐effective fish feeds are being sought, but there is also a particular need to determine the effects of exposed flavonoids on fish in the aquatic environment, as this is the main route of exposure of organisms to endocrine disruptors. This study evaluated the possible effects of these isoflavones on juveniles of Solea senegalensis and Solea solea. After 48–96 h of exposure, the acetylcholinesterase activity in the sole head tissues was measured, and the cholinesterase activity in juveniles of common sole (S. solea) was determined. Experiments were carried out to determine the optimal pH, investigate the specificity of three substrates (acetylthiocholine, butyrylthiocholine, propionylthiocholine) on cholinesterase activity and determine the kinetic parameters (Vmax and Km). The results obtained showed that neither genistein nor daidzein exposure to S. senegalensis and S. solea inhibited the activity of acetylcholinesterase at the tested concentrations (genistein: 1.25, 2.5, 5, 10 and 20 mg/L; daidzein: 0.625, 1.25, 2.5, 5 and 10 mg/L). Possible effects of isoflavones on juveniles of different species of flatfish were evaluated. After 48–96 h of exposure with genistein and daidzein, the acetylcholinesterase activity in the sole head tissues did not showed significant differences with the control. Likewise, optimal pH, specificity of three substrates (acetylthiocholine, butyrylthiocholine, and propionylthiocholine) on cholinesterase activity and kinetic parameters (Vmax and km) were determined on Solea solea. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the mesh selectivity of gillnets used in olive flounder (Paralichthys olivaceus) fishing by examining the distribution of total length (TL) across various mesh sizes. A marine fishing experiment was conducted at Gajin Harbor in Goseong County, Gangwon Province, employing experimental gear with four different mesh sizes: 90, 105, 135, and 150 mm. Mesh selectivity analysis involved a comparative assessment of selectivity curve methods through normal, log-normal, and bi-normal functions. Among these, the bi-normal function demonstrated the best fit for estimating the mesh selectivity curve within the SELECT model. The critical finding was the net size at which 50% of the minimum landing size (35 cm in TL) of olive flounder was selected, ranging from 108.7 to 121.1 mm. According to the bi-normal function curve, this size was estimated as 114.0 mm. Our findings indicate that using a mesh size larger than the theoretically estimated size in mesh selectivity analysis can further decrease the catch of immature individuals. These findings provide essential data for devising strategies to efficiently utilize and manage olive flounder resources. [ABSTRACT FROM AUTHOR]

Lymphocystis disease is frequently prevalent and transmissible in various teleost species worldwide due to lymphocystis disease virus (LCDV) infection, causing unsightly growths of benign lymphocystis nodules in fish and resulting in huge economic losses to aquaculture industry. However, the molecular mechanism of lymphocystis formation is unclear. In this study, LCDV was firstly detected in naturally infected flounder (Paralichthys olivaceus) by PCR, histopathological, and immunological techniques. To further understand lymphocystis formation, transcriptome sequencing of skin nodule tissue was performed by using healthy flounder skin as a control. In total, RNA-seq produced 99.36%-99.71% clean reads of raw reads, of which 91.11%-92.89% reads were successfully matched to the flounder genome. The transcriptome data showed good reproducibility between samples, with 3781 up-regulated and 2280 down-regulated differentially expressed genes. GSEA analysis revealed activation of Wnt signaling pathway, Hedgehog signaling pathway, Cell cycle, and Basal cell carcinoma associated with nodule formation. These pathways were analyzed to interact with multiple viral infection and tumor formation pathways. Heat map and protein interaction analysis revealed that these pathways regulated the expression of cell cycle-related genes such as ccnd1 and ccnd2 through key genes including ctnnb1, lef1, tcf3, gli2, and gli3 to promote cell proliferation. Additionally, cGMP-PKG signaling pathway, Calcium signaling pathway, ECMreceptor interaction, and Cytokine-cytokine receptor interaction associated with nodule formation were significantly down-regulated. Among these pathways, tnfsf12, tnfrsf1a, and tnfrsf19, associated with pro-apoptosis, and vdac2, which promotes viral replication by inhibiting apoptosis, were significantly upregulated. Visual analysis revealed significant down-regulation of cytc, which expresses the pro-apoptotic protein cytochrome C, as well as phb and phb2, which have anti-tumor activity, however, casp3 was significantly up-regulated. Moreover, bcl9, bcl11a, and bcl-xl, which promote cell proliferation and inhibit apoptosis, were significantly upregulated, as were fgfr1, fgfr2, and fgfr3, which are related to tumor formation. Furthermore, RNA-seq data were validated by qRT-PCR, and LCDV copy numbers and expression patterns of focused genes in various tissues were also investigated. These results clarified the pathways and differentially expressed genes associated with lymphocystis nodule development caused by LCDV infection in flounder for the first time, providing a new breakthrough in molecular mechanisms of lymphocystis formation in fish. [ABSTRACT FROM AUTHOR]

Olive flounders are susceptible to annual outbreaks of streptococcosis, which accounts for approximately 10% of all fish farm diseases and is associated with high mortality rates. The development of an antibiotic therapy against streptococcosis is thus necessary. This study determined the therapeutic effects of varying cephalexin concentrations in Streptococcus parauberis-infected olive flounders and evaluated its histopathological toxicity and residual concentration in the fish. Compared with the control group, the 200 and 800 mg/kg cephalexin groups showed significant mean survival rates of approximately 10% and 30%, respectively, and the 400 mg/kg group showed the highest survival rate of approximately 40%. The average residual cephalexin concentration in muscle samples on day 1 post-cephalexin administration was 13.21 µg/kg, showing a rapid decrease. At the optimum water temperature (25°C), cephalexin was rapidly metabolized within 24 hr of its administration being terminated, and most of it was excreted from the bodies of the fish. A histopathological analysis showed that the oral administration of cephalexin did not lead to specific inflammatory lesions, and there were no significant differences between the treatment and control groups. Our novel findings suggest that cephalexin is a promising candidate for treating streptococcosis outbreaks in fish farms. [ABSTRACT FROM AUTHOR]

Simple Summary: The present research enriches our comprehension of the mitogenomic genetic features, genetic diversity, evolutionary past, and conservation prerequisites of Psettodes flatfishes on a global scale. This study focuses on the matrilineal evolutionary path of these primitive groups, with a specific emphasis on the complete mitogenome of the Psettodes belcheri and casting light on its genetic composition, structural traits, and evolutionary chronicle. Exploring genetic variations and phylogenetic relationships uncovers the intricate evolutionary links between Psettodes species and their broader context within the Pleuronectiformes species. The complex interplay of hydrographic conditions, ocean currents, and ecological factors emerges as pivotal in shaping the evolutionary landscape of these flatfishes. Given the potential consequences for conservation, this study highlights the necessity for a holistic comprehension of marine environments and the ramifications of climate change and human interventions on flatfish species. The mitogenomic evolution of the Psettodes flatfishes is still poorly known from their range distribution in eastern Atlantic and Indo-West Pacific Oceans. The study delves into the matrilineal evolutionary pathway of these primitive flatfishes, with a specific focus on the complete mitogenome of the Psettodes belcheri species, as determined through next-generation sequencing. The mitogenome in question spans a length of 16,747 base pairs and comprises a total of 37 genes, including 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and a control region. Notably, the mitogenome of P. belcheri exhibits a bias towards AT base pairs, with a composition of 54.15%, mirroring a similar bias observed in its close relative, Psettodes erumei, which showcases percentages of 53.07% and 53.61%. Most of the protein-coding genes commence with an ATG initiation codon, except for Cytochrome c oxidase I (COI), which initiates with a GTG codon. Additionally, four protein-coding genes commence with a TAA termination codon, while seven others exhibit incomplete termination codons. Furthermore, two protein-coding genes, namely NAD1 and NAD6, terminate with AGG and TAG stop codons, respectively. In the mitogenome of P. belcheri, the majority of transfer RNAs demonstrate the classical cloverleaf secondary structures, except for tRNA-serine, which lacks a DHU stem. Comparative analysis of conserved blocks within the control regions of two Psettodidae species unveiled that the CSB-II block extended to a length of 51 base pairs, surpassing the other blocks and encompassing highly variable sites. A comprehensive phylogenetic analysis using mitochondrial genomes (13 concatenated PCGs) categorized various Pleuronectiformes species, highlighting the basal position of the Psettodidae family and showed monophyletic clustering of Psettodes species. The approximate divergence time (35−10 MYA) between P. belcheri and P. erumei was estimated, providing insights into their separation and colonization during the early Miocene. The TimeTree analysis also estimated the divergence of two suborders, Psettodoidei and Pleuronectoidei, during the late Paleocene to early Eocene (56.87 MYA). The distribution patterns of Psettodes flatfishes were influenced by ocean currents and environmental conditions, contributing to their ecological speciation. In the face of climate change and anthropogenic activities, the conservation implications of Psettodes flatfishes are emphasized, underscoring the need for regulated harvesting and adaptive management strategies to ensure their survival in changing marine ecosystems. Overall, this study contributes to understanding the evolutionary history, genetic diversity, and conservation needs of Psettodes flatfishes globally. However, the multifaceted exploration of mitogenome and larger-scale genomic data of Psettodes flatfish will provide invaluable insights into their genetic characterization, evolutionary history, environmental adaptation, and conservation in the eastern Atlantic and Indo-West Pacific Oceans. [ABSTRACT FROM AUTHOR]

Coastal habitats play a key role in the early life stages of flatfish species, with the quantity and quality of the food they supply being central. However, survival and sufficient development until metamorphosis depend upon obtaining certain essential long-chain polyunsaturated fatty acids (LC-PUFAs). We focused this literature review on flatfish requirements, supplies and availability of three most important LC-PUFAs: DHA (docosahexaenoic acid; 22:6n-3), EPA (eicosapentaenoic acid; 20:5n-3) and ARA (arachidonic acid; 20:4n-6). First, based on aquaculture research, we summarize their importance for larval development and highlight that Solea spp. are the only marine flatfish known to synthesize DHA, which influences their LC-PUFA requirements. Second, analysis of published LC-PUFA contents in the flatfish larvae prey indicates that they most likely cannot synthesize essential LC-PUFA. They show large differences in DHA and EPA content between species, study sites, feeding environments and developmental stages. Third, LC-PUFA contents of phytoplankton, as the main source of essential LC-PUFAs for the prey of flatfish larvae, vary with species, seasons, nutrient availabilities and temperature. However, flatfish larvae prey probably overcome some limiting conditions by targeting species with high LC-PUFA contents through preferential assimilation and/or selective feeding on prey quality as done by flatfish larvae at a higher trophic level. Fourth, in the scarcity of available data, we propose future research avenues. One of them could investigate relations between availability of LC-PUFAs and plankton biodiversity, which appears to be key in meeting flatfish larvae requirements in coastal habitats and may be influenced by the current increasing human pressure. [ABSTRACT FROM AUTHOR]

The selection of a suitable method for tagging fish with transmitters is essential to ensure the feasibility of telemetry studies. Here, using a micro-acoustic transmitter, we examined the effects of tagging methods such as external attachment and surgical implantation on tag retention, and growth and survival of hatchery-reared spotted halibut at the release size (ca. 8–10 cm in total length). Fish with surgical implantation showed higher survival and retention rates than those with external attachments. However, the tagging methods did not influence the growth of the tagged fish. These findings indicated that surgical implantation of acoustic transmitters can be applied to small-sized spotted halibut. Overall, the findings can enhance the study about post-release movement of hatchery-reared fish at the release size to manage and conserve flatfish stocks. [ABSTRACT FROM AUTHOR]

Vibrio anguillarum (V. anguillarum) is a bacterium that seriously harms flounder and other aquaculture species. Vaccination is an effective means of preventing vibriosis and is mainly administered by intraperitoneal injection. Effective antigen processing at the initial stage of immunization is essential to elicit adaptive immune responses and improve vaccine efficacy. To understand the early immune response of flounder caused by inactivated V. anguillarum, we detected the transcriptome profiles of the cells in the peritoneal cavity (PoPerCs) after inactivated V. anguillarum immunization. More than 10 billion high-quality reads were obtained, of which about 89.33% were successfully mapped to the reference genome of flounder. A total of 1985, 3072, 4001, and 5476 differentially expressed genes were captured at 6, 12, 24, and 48 h post immunization, respectively. The hub module correlated with the immunization time was identified by WGCNA. GO and KEGG analysis showed that hub module genes were abundantly expressed in various immune-related aspects, including the response to stimuli, the immune system process, signal transducer activity, autophagy, the NOD-like receptor signaling pathway, the toll-like receptor signaling pathway, the T cell receptor signaling pathway, and Th17 cell differentiation. Additionally, genes related to Th cell differentiation are presented as heatmaps. These genes constitute a complex immune regulatory network, mainly involved in pathogen recognition, antigen processing and presentation, and Th cell differentiation. The results of this study provide the first transcriptome profile of PoPerCs associated with inactivated V. anguillarum immunity and lay a solid foundation for further studies on effective V. anguillarum vaccines. [ABSTRACT FROM AUTHOR]

Inclusion of various sources of additives in aquafeeds is practically helpful to elevate the growth performance and disease resistance of aquatic animals. An 8‐week feeding trial was conducted to determine the inclusion effects of phyto‐additives (yacon, ginger, and blueberry) into diets on olive flounder growth, feed utilization, chemical composition, and plasma chemistry, and to challenge test against Edwardsiella tarda in comparison to a commercial probiotic SUP (Super lacto®). Six hundred juvenile olive flounder were randomly allocated into 15, 50 L flow‐through tanks (40 fish per tank). Five experimental diets were formulated. No additive was included in the control (Con) diet. One percent of yacon, ginger, and blueberry powders, and 0.5% Super Lacto® were included at the expense of wheat flour and water in the Con diet, also referred to as the YCP (yacon powder), GGP (ginger powder), BBP (blueberry powder), and SUP diets, respectively. All experimental diets were hand‐fed to triplicate groups of fish twice a day until they were visually satiated for a period of 8 weeks. Following the 4‐ and 8‐week feeding trials, 10 and 20 fish were taken from each tank and artificially infected with E. tarda, and then survival was monitored for the next 6 and 8 days after infection, respectively. At the end of the 8‐week feeding trial, no significant difference was observed in weight gain, feed consumption, feed utilization, chemical composition, and plasma chemistry in olive flounder. However, the survival of olive flounder fed the GGP diet was significantly (p < 0.004 and p < 0.02, respectively) higher than that of fish fed the SUP, BBP, and Con diets, and the SUP and Con diets after the 4‐ and 8‐week feeding trials, respectively, according to the Kaplan–Meier survival curve. In conclusion, phyto‐additive, especially GG, can be used as an effective immunostimulant in the olive flounder diet at the occurrence of E. tarda. [ABSTRACT FROM AUTHOR]

Olive flounder (Paralichthys olivaceus) muscle satellite cells (OFMCs) were obtained by enzymatic primary cell isolation and the explant method. Enzymatic isolation yielded cells that reached 80% confluence within 8 days, compared to 15 days for the explant method. Optimal OFMC growth was observed in 20% fetal bovine serum at 28 °C with 0.8 mM CaCl2 and the basic fibroblast growth factor (BFGF) to enhance cell growth. OFMCs have become permanent cell lines through the spontaneous immortalization crisis at the 20th passage. Olive flounder skeletal muscle myoblasts were induced into a mitogen-poor medium containing 2% horse serum for differentiation; they fused to form multinucleate myotubes. The results indicated complete differentiation of myoblasts into myotubes; we also detected the expression of the myogenic regulatory factors myoD, myogenin, and desmin. Upregulation (Myogenin, desmin) and downregulation (MyoD) of muscle regulation factors confirmed the differentiation in OFMCs. [ABSTRACT FROM AUTHOR]

Hirame novirhabdovirus (HIRRV), which mainly infects the olive flounder (Paralichthys olivaceus), is considered to be one of the most serious viral pathogens threatening the global fish culture industry. However, little is known about the mechanism of host-pathogen interactions at the metabolomic level. In this study, in order to explore the metabolic response of olive flounder to HIRRV infection, liquid chromatography mass spectrometry (LC-MS) was used to detect the changes of endogenous compounds of the olive flounder after HIRRV infection. A total of 954 unique masses were obtained, including 495 metabolites and 459 lipids. Among them, 7 and 173 qualified differential metabolites were identified at 2 days and 7 days post-infection, respectively. Distinct metabolic profiles were observed along with viral infection. At the early stage of infection, only a few metabolites were perturbed. Among them, the level of inosine and carnosine were increased and the potential antiviral ability of these two metabolites was further confirmed by exogenous addition experiment. At the late stage of HIRRV infection, the metabolic profiles changed remarkably. The changes in amino acids and nucleotides especially the 7-methylguanine also accelerated the amplification of viral particles. And the down-regulation of glutathione (GSH) implied an elevated level of ROS (reactive oxygen species) that attenuated the immune system of flounders. HIRRV also induced the accumulation of purine and reduction of pyrimidine, and elevated LPC and LPE levels. The unbalanced purine/pyrimidine and altered lipid profile may be beneficial for the replication and infection of HIRRV at the late stage of infection. These findings provide new insights into the pathogenic mechanism of HIRRV infection in olive flounder. [ABSTRACT FROM AUTHOR]

Sympatric flatfish predators may partition their resources in coastal environments to reduce competition and maximise foraging efficiency. However, the degree of spatial and temporal consistency in their trophic ecology is not well understood because dietary studies tend to overlook the heterogeneity of consumed prey. Increasing the spatial and temporal scale of dietary analyses can thus help to resolve predator resource use. We applied a stomach content and multi‐tissue (liver and muscle) stable isotope (δ13C, δ15N and δ34S) approach to investigate the feeding habits of two co‐occurring flatfish predators, common dab (Limanda limanda) and European plaice (Pleuronectes platessa), across four bays on the Northumberland coast (UK) over short (hours), medium (days) and long (months) temporal scales. Stomach content analyses showed spatial consistencies in predator resource use, whereas stable isotope mixing models revealed considerable inter‐bay diet variability. Stomach contents also indicated high dietary overlap between L. limanda and P. platessa, while the stable isotope data yielded low to moderate levels of overlap, with cases of complete niche separation. Furthermore, individual specialisation metrics indicated consistently low levels of specialisation among conspecifics over time. We document changes in resource partitioning in space and time, reflecting diet switching in response to local and temporal fluctuations of patchily distributed prey. This study highlights how trophic tracers integrated at multiple temporal and spatial scales (within tens of kilometres) provide a more integrative approach for assessing the trophic ecology of sympatric predators in dynamic environments. [ABSTRACT FROM AUTHOR]

Simple Summary: Histology and stereology were used to estimate the sexual maturity phase for the European Plaice, as well as a description of the oogenesis cycle and size at first maturity. This study provides a method to accurately determine a key parameter for fisheries management that may be used for other species. The following paper gives a detailed description of the oogenesis cycle for the European Plaice (Pleuronectes platessa), from oogonia to post-ovulatory follicle, including ovarian follicle and zona pellucida sizes. Noteworthy particularities were the difficulty in identifying cortical alveoli due to their very small size. Quantitative histology (stereology) on histological slides was used to determine a first size at maturity for females from the English Channel, which was found to be smaller compared to the literature (19 cm). Stereology also determined a first spawning event starting in January, with a peak in February and ongoing until March. Moreover, the use of stereology showed misclassifications for individuals categorized into a maturity phase using a macroscopic visual method. Misclassifications were found with individuals that had spawned (D) but were put under the immature (A) phase, and individuals in development (B) classified under D. [ABSTRACT FROM AUTHOR]

Application of feed stimulants is very helpful to increase the feed intake of fish, especially in the development of low fish meal (FM) diets. FM replacement effect by various plant protein sources (corn gluten meal (CGM), soy protein concentrate (SPC), and corn protein concentrate (CPC)) in diets with an addition of jack mackerel meal (JMM) as feed stimulants on growth, feed availability, and biochemical composition of olive flounder was elucidated. An experimental design of two-way (two replacement levels (25% and 50%) × 3 replacement sources (CGM, SPC, and CPC)) analysis of variance was adopted. Seven diets were formulated. Amount of 60% FM was contained in the control (Con) diet. In the Con diet, 25% and 50% FM were replaced by CGM, SPC, and CPC with an addition of 12% JMM as feed stimulants, referred to as the CGM25, CGM50, SPC25, SPC50, CPC25, and CPC50 diets, respectively. Four hundred and twenty juvenile fish were distributed into 21 flow-through tanks. All diets were assigned to triplicate groups of fish. Fish were hand-fed to satiation twice a day for 56 days. Both dietary replacement levels and sources had statistical effect on weight gain (P < 0.0001 and P < 0.045 , respectively), specific growth rate (SGR) (P < 0.0001 and P < 0.033), and feed consumption (P < 0.0001 and P < 0.03) of fish. Dietary increased FM replacement levels lowered weight gain, SGR, and feed consumption of fish. Weight gain, SGR, and feed consumption of fish fed the Con and CGM25 diets were statistically (P < 0.05) greater than those of fish fed the CGM50, SPC50, and CPC50 diets. Both replacement level and source had no statistical effect on feed utilization, biochemical composition except for statistical effect of replacement source on glycine content of fish, and lysozyme and superoxide dismutase (SOD) activities of fish. FM up to 25% could be substituted with CGM, SPC, and CPC in the olive flounder feeds supplemented with 12% JMM as feed stimulants without compromising growth, feed utilization, and lysozyme and SOD activities. [ABSTRACT FROM AUTHOR]

The third part of the illustrated keys for the classification of the brachyuran crabs (Crustacea, Brachyura) of Cuba is presented. The keys and original figures for the classification of the families of the Section Eubrachyura, Subsection Heterosomata (continuation) are included, Geryonidae (one genus and one species); Palicidae (one genus and 8 species); Parthenopidae (7 genera and 10 species); Pilumnidae, (two genera and 14 species); and Portunidae (9 genera and 26 species), totaling 5 families, 20 genera and 59 species. [ABSTRACT FROM AUTHOR]

Simple Summary: Low temperature is an often overlooked stress that many fish face due to both natural and anthropogenic causes. Japanese flounder (Paralichthys olivaceus) is an economically important aquaculture fish species broadly cultivated in east Asia, mainly along the coast of the Bohai and Yellow Seas in China, as well as the coast of Korea and east Japan. Natural and cultivated P. olivaceus may suffer from cold stress during the winter months. In this study, modulated transcriptomic responses to 10 °C acute cold stress were investigated in the gills, hearts, livers, and spleens of P. olivaceus. Based on transcriptome and weighted gene coexpression network analysis, tissue-specific cold responsive modules (CRMs) were identified, which revealed a cascade of specific cellular responses to cold stress in different tissues. Our results illustrate the diverse and modulated regulation of the cellular process and stress response to low temperature, which provide essential insights for the conservation and cultivation of P. olivaceus in cold water. Low temperature is among the important factors affecting the distribution, survival, growth, and physiology of aquatic animals. In this study, coordinated transcriptomic responses to 10 °C acute cold stress were investigated in the gills, hearts, livers, and spleens of Japanese flounder (Paralichthys olivaceus), an important aquaculture species in east Asia. Histological examination suggested different levels of injury among P. olivaceus tissues after cold shock, mainly in the gills and livers. Based on transcriptome and weighted gene coexpression network analysis, 10 tissue-specific cold responsive modules (CRMs) were identified, revealing a cascade of cellular responses to cold stress. Specifically, five upregulated CRMs were enriched with induced differentially expressed genes (DEGs), mainly corresponding to the functions of "extracellular matrix", "cytoskeleton", and "oxidoreductase activity", indicating the induced cellular response to cold shock. The "cell cycle/division" and "DNA complex" functions were enriched in the downregulated CRMs for all four tissues, which comprised inhibited DEGs, suggesting that even with tissue-specific responses, cold shock may induce severely disrupted cellular functions in all tissues, reducing aquaculture productivity. Therefore, our results revealed the tissue-specific regulation of the cellular response to low-temperature stress, which warrants further investigation and provides more comprehensive insights for the conservation and cultivation of P. olivaceus in cold water. [ABSTRACT FROM AUTHOR]

Otolith chemistry is a useful natural tracer for discerning habitat‐use of estuarine fishes. For Southern Flounder Paralichthys lethostigma, recent otolith chemistry studies have revealed a diversity of residency patterns across salinity gradients. However, the contribution of recruits with specific residency patterns to fisheries is poorly understood. The objectives of this study were to (1) use otolith chemistry from fishery‐independent and fishery‐dependent collections in Mobile Bay, Alabama, to classify lifetime residency patterns (i.e., freshwater, transient, estuarine) in Southern Flounder collected across a large estuarine salinity gradient (0–30 psu); (2) to test if Southern Flounder exhibited resident or migratory behavior by determining if lifetime residency patterns in fishery‐independent samples matched expected salinity patterns in the region of collection after accounting for annual variation in river discharge; and (3) to examine which residency patterns contributed to the commercial and recreational Southern Flounder fisheries in nearby coastal waters. Age‐0 residency patterns in fishery‐independent samples were strongly correlated with region of collection and annual river discharge, suggesting that the majority of Southern Flounder had resided in the same region in which they spent their age‐0 growth phase. Southern Flounder with a combination of freshwater and estuarine salinity signals and classified as "transient" did not appear to have conducted large‐scale movements across salinity gradients, but instead resided in regions of the estuary experiencing seasonal fluctuations in salinity. The majority (57%) of commercially and recreationally harvested Southern Flounder were transients, while a minority (39%) were estuarine residents and lifetime freshwater residents (4%) were rarely harvested. Results from this study suggest that Southern Flounder settle in and remain in the certain habitats during the estuarine residency phase. Given the lack of movement across habitats, future efforts to understand how habitat‐specific conditions (e.g., abiotic, biotic, fishing exploitation) affect vital rates seems warranted for a species currently experiencing population declines. [ABSTRACT FROM AUTHOR]