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Over the past decade, an increasing number of studies have emphasized the importance of the host microbiome in influencing organismal health and development. Aligned with this understanding, our study aimed to investigate the potential association between the turbot (Scophthalmus maximus) phenotypic traits and the post-larval bacteriome. Turbot post-larvae were sampled from twenty randomly selected production cycles thirty days after hatching (DAH) across multiple post-larval production batches over a three-month period (April to June). Fish were selectively sampled based on five phenotypic traits, namely, normal, large, small, malformed, and depigmented. Our results showed that small-sized post-larvae had significantly higher bacterial phylogenetic diversity in their bacterial communities than all other phenotypes. A more in-depth compositional analysis also revealed specific associations between certain bacterial taxa and fish phenotypes. For example, the genera Aliivibrio and Sulfitobacter were enriched in small-sized post-larvae, while the family Micrococcaceae were predominantly found in larger post-larvae. Furthermore, genus Exiguobacterium was linked to depigmented larvae, and genus Pantoea was more prevalent in normal post-larvae. These observations underscore the importance of further research to understand the roles of these bacterial taxa in larval growth and phenotypic differentiation. Such insights could contribute to developing microbiome modulation strategies, which may enhance turbot post-larval health and quality and improve larviculture production. [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]

Chemical communication through olfaction is crucial for fish behaviours, mediating in socio-sexual behaviours as reproduction. Turbot, a flatfish with significant aquaculture production, possesses a well-developed olfactory system from early developmental stages. After metamorphosis, flatfish acquire their characteristic bilateral asymmetry with an ocular side facing the open water column, housing the dorsal olfactory rosette, and a blind side in contact with the sea bottom where the ventral rosette is located. This study aimed to address the existing gap in specific histological, ultrastructural, lectin-histochemical and immunohistochemical studies of the turbot olfactory rosettes and olfactory bulbs. We examined microdissected olfactory organs of adult turbots and premetamorphic larvae by using routine histological staining techniques, and a wide array of lectins and primary antibodies against G-proteins and calcium-binding proteins. We observed no discernible structural variations in the olfactory epithelium between rosettes, except for the dorsal rosette being larger in size compared to the ventral rosette. Additionally, the use of transmission electron microscopy significantly improved the characterization of the adult olfactory epithelium, exhibiting high cell density, small cell size, and a wide diversity of cell types. Moreover, specific immunopositivity in sensory and non-sensory cells provided us of essential information regarding their olfactory roles. The results obtained significantly enriched the scarce morphological and neurochemical information available on the turbot olfactory system, revealing a highly complex olfactory epithelium with distinct features compared to other teleost species, especially with regard to olfactory cell distribution and immunolabelling patterns. [ABSTRACT FROM AUTHOR]

The diversity of Tenacibaculum maritimum in Chile remains poorly understood, particularly in terms of antigenic and genetic diversity. This information is crucial for the future development of a vaccine against tenacibaculosis and would increase understanding of this important fish pathogen. With this aim, the biochemical, antigenic, and genetic characteristics were analysed for 14 T. maritimum isolates, recovered from diseased Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) farmed in Chile between 1998 and 2022. Biochemical analysis showed a homogeneity among all the Chilean T. maritimum isolates and all four other strains included for comparison purposes. Serological characterization using dot‐blot assaying revealed antigenic heterogeneity with the use of unabsorbed antisera. The majority of isolates showed cross‐reactions, identifying three main serological patterns. When the PCR‐based serotyping scheme was performed, the existence of antigenic heterogeneity was confirmed. Four Atlantic salmon isolates were 4–0; and most isolates, including the rainbow trout isolate, were 3–1 (n = 9). A turbot (Scophthalmus maximus) isolate was 1–0. Using an existing Multilocus Sequence Typing system, two newly identified sequence types (ST193 and ST198) in the database were detected. ST193 encompassed nine isolates obtained from Atlantic salmon and rainbow trout, while ST198 regrouped four isolates, all retrieved from diseased Atlantic salmon in 2022. These findings highlight significant antigenic and genetic diversity among the Chilean isolates. This information is useful for epizootiology and the selection of suitable candidate strain(s) for vaccine development against tenacibaculosis caused by T. maritimum in Chilean salmon farming. [ABSTRACT FROM AUTHOR]

During embryonic development, vitamins are involved in energy metabolism and protein synthesis, while cathepsins and antioxidant defense play key roles in yolk degradation and protecting fish embryos from oxidative damage. This study aimed to investigate the consumption of vitamins (A, B1, B2, C, D, and E), ontogenesis of cathepsins, and antioxidant capacity in developing embryos of turbot. In this study, embryos were collected over time from 2.3 to 102.5 h (i.e., hatching) after fertilization for vitamins, cathepsins, and antioxidant capacity analyses. Results showed that the embryonic growth rate in the cleavage stage (CS) was faster than in other stages, while that in the segmentation stage (SS) was lower than in other stages. Embryos displayed higher demands on VA during blastula stage (BS), gastrula stage (GS), the early SS, and hatching day (HD), VB1 at CS; VB2 at BS, GS, SS, and HD; VD at CS and SS; VE at CS, BS, and the late SS; and Vc during entire periods. Cathepsins A (CA) showed a high level at early SS, suggesting its involvement in yolk degradation. Cathepsins B (CB) and cathepsins D (CD) were highly active at GS, suggesting an active apoptosis process. CA, CB, CD, and cathepsins L (CL) all kept low levels in CS, revealing low protein demand during the cleavage process. On the whole, the predominant antioxidant enzymes were superoxide dismutase (SOD) and malondialdehyde (MDA) from CS to SS; SOD, MDA, glutathione peroxidase (GSH-Px), and catalase (CAT) during SS; and GSH-Px and CAT during HD. In conclusion, the fastest growth rate and the slowest growth rate of embryos occurred in CS and SS, respectively, being consistent with energy allocation. Vitamin consumption and cathepsin ontogenesis were stage-specific. Oxidative damage on embryos was relatively less at CS, but larger at SS and HD. [ABSTRACT FROM AUTHOR]

Hsp40–Hsp70 typically function in concert as molecular chaperones, and their roles in post-infection immune responses are increasingly recognized. However, in the economically important fish species Scophthalmus maximus (turbot), there is still a lack in the systematic identification, interaction models, and binding site analysis of these proteins. Herein, 62 Hsp40 genes and 16 Hsp70 genes were identified in the turbot at a genome-wide level and were unevenly distributed on 22 chromosomes through chromosomal distribution analysis. Phylogenetic and syntenic analysis provided strong evidence in supporting the orthologies and paralogies of these HSPs. Protein–protein interaction and expression analysis was conducted to predict the expression profile after challenging with Aeromonas salmonicida. dnajb1b and hspa1a were found to have a co-expression trend under infection stresses. Molecular docking was performed using Auto-Dock Tool and PyMOL for this pair of chaperone proteins. It was discovered that in addition to the interaction sites in the J domain, the carboxyl-terminal domain of Hsp40 also plays a crucial role in its interaction with Hsp70. This is important for the mechanistic understanding of the Hsp40–Hsp70 chaperone system, providing a theoretical basis for turbot disease resistance breeding, and effective value for the prevention of certain diseases in turbot. [ABSTRACT FROM AUTHOR]

Simple Summary: The phenomenon of cellular vacuolization is closely related to apoptosis. During the culture of marine fish cell lines, an interesting phenomenon was found that the addition of excessive concentrations of serum to the culture medium could lead to the vacuolization of marine fish cells. However, this vacuolization phenomenon will disappear as the number of cell passages increases. Transcriptome sequencing was used to reveal the relationship between this transiently reversible phenomenon of cellular vacuolization and two influential factors, serum concentration and trypsin digestion. This study provides new insights into the mechanisms of cellular vacuolization and serves as a reference for the culture of marine fish cell lines. As an important research tool, cell lines play a vital role in life science research, medical research, and drug development. During the culture of the Scophthalmus maximus head kidney (TK) cell line, we found a phenomenon of cell vacuolization caused by excessive serum concentration. Moreover, the vacuolization of the cells gradually disappeared after passage by trypsin digestion. In clarifying the formation mechanism of this reversible cellular vacuolation, transcriptomics was utilized to explore the mechanism of cell vacuolization caused by excessive serum concentration. Transcriptome analysis indicated that excessive serum concentration could cause the up-regulated expression of PORCN and other genes to promote cell proliferation. Compared with cells whose vacuolization disappeared after trypsin digestion and passage, the expression of mitosis-related genes (BUB1, ttk, Mad2, Cdc20, CDK1, CCNB1), nuclear stability-related genes LMNB1 and tissue stress and repair-related genes HMMR in vacuolated cells caused by excessive serum concentration was significantly up-regulated. There is a regulatory system related to adaptation and stress repair in the cells, which can maintain cell stability to a certain extent. This study provides a theoretical basis for the stable culture of fish cell lines and the solution to the problem of cell vacuolation. [ABSTRACT FROM AUTHOR]

Objective: The waterless transport of live fish has changed the present situation of live‐fish transport. However, the waterless transport environment may cause stress in fish. This research evaluated the effect of tea polyphenol–trehalose (TPT) coating solutions on Turbot Scophthalmus maximus during waterless transport. Methods: After cold acclimation, Turbot were coated and subsequently transported in a waterless environment for 18 h. Physiological and biochemical parameters were measured, including lysozyme (LZM) and immunoglobulin M (IgM) activities, serum creatinine (Cr) and uric acid (UA) concentrations, and nutritional flavor. Result: The results showed that the nonspecific immunity of Turbot was inhibited during the waterless transport; the LZM activity first increased and then decreased, and the serum Cr and UA concentrations significantly increased. In addition, the waterless transport promoted the breakdown of Turbot flesh proteins, leading to changes in nucleotides and free amino acids (FAAs). After waterless transport, the LZM and IgM activities in the TPT‐treated Turbot were higher than those in the control group (CK), and the changes in FAA content and nucleotides were smaller than those observed in the CK group. Conclusion: This study shows that the use of TPT coating solution can reduce the impact of waterless transportation stress on the immune and metabolic functions of Turbot and can maintain the meat quality and flavor of Turbot. Impact statementWaterless transportation of live fish is considered as a green and economical solution to achieve high survival rates and quantity. In this article, we address a new method (coatings) to handle live Turbots in waterless transport, this method can reduce transportation stress and maintain the quality of Turbot. [ABSTRACT FROM AUTHOR]

Microplastic (MP) pollution has become a health concern subject in recent years. Althoughann increasing number of studies about the ingestion of microplastics by fish, research on the oxidative stress response to MPs in natural environments is quite limited. In this study, the identification and characterization of MPs in gill (G), muscle tissues (M), and gastrointestinal tract (GI) of turbot (Scophthalmus maximus) were evaluated. Oxidative damage of MPs on the brain (B), liver (L), gill (G), and muscle (M) tissues as well as their effect on superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), paraoxonase (PON), arylesterase (AR) myeloperoxidase (MPO), and malondialdehyde (MDA) biomarkers were evaluated. The potential transmission of MPs from muscle tissues to humans was examined. Results showed that gills contain the highest amounts of MPs, ethylene propylene is the most dominant polymer type, black and blue are the most common MP color, fiber is the most common shape, and 50-200 µm is the most common MP size. Results showed that MPs cause oxidative stress of tissues with inhibiting effect on enzyme activities and promoting impact on lipid peroxidation. The oxidative damage mostly affected the liver (detoxification organ) followed by gill tissue. The intake of MPS in the European Union was estimated by EFSA as 119 items/year, while in Turkey it is 47.88 items/year. This study shows that more research is needed in terms of ecosystem health and food chain safety. The risk assessment of MPs in living organisms and environmental matrices including food safety and human health should be considered a public health issue. [ABSTRACT FROM AUTHOR]

To evaluate the effects of probiotics following the administration of different antibiotics on turbot Scophthalmus maximus, a 35-day culture experiment with dietary feeding with antibiotics and probiotics was conducted. Groups E and F received enrofloxacin and florfenicol for 15 days respectively, followed by supplementation of probiotics B. coagulans for 20 days. Fish growth, immunity, antibiotic resistance genes (ARGs), and intestinal microflora were investigated. Significant growth was observed, and the expression of IL-8 and TNF-α was significantly upregulated in most of examined organs in both groups, indicating B. coagulans supplementation improves the growth performance. The four analyzed ARGs were downregulated with B. coagulans supplementation though they were upregulated with antibiotic administration. The administration of florfenicol decreased Vibrio abundance but increased the abundance of potentially pathogenic bacteria such as Clostridia, Turicibacter, and Erysipelotrichia, and the administration of enrofloxacin increased the abundance of Clostridia. Notably, B. coagulans supplementation decreased the abundance of opportunistic pathogens such as Clostridia, Turicibacter, Erysipelotrichales, and Lachnospiraceae, indicating B. coagulans may help restore homeostasis of intestinal microflora. Overall, the present study results revealed the probiotic B. coagulans yields a beneficial effect on juvenile turbot and provides a novel therapeutic approach to reduce negative effects caused by antibiotics in fish. [ABSTRACT FROM AUTHOR]

The Aeromonas salmonicida is responsible for causing furunculosis in various fish species. Furunculosis is a ubiquitous disease that affects the aquaculture industry and causes the mass mortality of turbot. Vibrio vulnificus is a pathogen that causes skin ulcers and hemorrhagic septicemia in fish, resulting in significant mortality in aquaculture. In this study, we have established a bivalent inactivated vaccine against A. salmonicida and V. vulnificus with Montanide™ ISA 763 AVG as an adjuvant. This bivalent inactivated vaccine was used to immunize turbot by intraperitoneal injection, and the relevant immune indexes were detected. The results demonstrate that the bivalent inactivated vaccine exhibited a relative percent survival (RPS) of 77% following A. salmonicida and V. vulnificus intraperitoneal challenge. The vaccinated group exhibited higher levels of acid phosphatase activity and lysozyme activity compared to the control group. ELISA results showed a significant increase in serum antibody levels in immunized turbot, which was positively correlated with immunity. In the kidney tissue, related immune genes (TLR5, CD4, MHCI and MHCII) were up-regulated significantly, showing that the vaccine can induce cellular and humoral immune responses in turbot. In conclusion, the bivalent inactivated vaccine against A. salmonicida and V. vulnificus was immunogenic, efficiently preventing turbot from infection, which has the potential to be applied in aquaculture. [ABSTRACT FROM AUTHOR]

Introduction: Animal welfare in aquaculture is becoming increasingly important, and detailed knowledge of the species concerned is essential for further optimization on farms. Every organism is controlled by an internal clock, the circadian rhythm, which is crucial for metabolic processes and is partially influenced by abiotic factors, making it important for aquaculture practices. Objective: In order to determine the circadian rhythm of adult turbot (Scophthalmus maximus), blood samples were collected over a 24-h period and plasma metabolite profiles were analyzed by 1H-NMR spectroscopy. Methods: The fish were habituated to feeding times at 9 am and 3 pm and with the NMR spectroscopy 46 metabolites could be identified, eight of which appeared to shift throughout the day. Results: We noted exceptionally high values around 3 pm for the amino acids isoleucine, leucine, valine, phenylalanine, lysine, and the stress indicator lactate. These metabolic peaks were interpreted as either habituation to the usual feeding time or as natural peak levels in turbot in a 24-h circle because other indicators for stress (glucose, cortisol and lysozymes) showed a stable baseline, indicating that the animals had no or very little stress during the experimental period. Conclusion: This study provides initial insights into the diurnal variation of metabolites in adult turbot; however, further studies are needed to confirm present findings of possible fluctuations in amino acids and sugars. Implementing optimized feeding times (with high levels of sugars and low levels of stress metabolites) could lead to less stress, fewer disease outbreaks and overall improved fish welfare in aquaculture facilities. [ABSTRACT FROM AUTHOR]

In this article, the effect of active coatings of flaxseed gum (FG) and sodium alginate (SA) containing carvacrol (CA) on the quality of turbot (Scophthalmus maximus) after storage at 4 °C for 18 days was evaluated. The experimental results showed that FG/SA-CA could effectively inhibit the growth of microorganisms. At the same time, FG/SA-CA reduced the value of odorous-related compounds including thiobarbituric acid reactive substances (TBARS), total volatile base nitrogen (TVB-N), and K values. The FG/SA-CA significantly delayed the oxidation of myofibrillar protein (MP) through controlling the development of carbonyl groups and maintaining a high content of sulfhydryl groups. Thus, FG/SA-CA inhibits the growth of spoilage microorganisms, maintains the structure of the protein, and extends the refrigerated shelf life of turbot. [ABSTRACT FROM AUTHOR]

Electrical pulse trawling is an alternative to conventional beam trawling for common sole (Solea solea), with substantially less discards, lower fuel consumption, and reduced impact on the benthic ecosystem. Pulsed electric fields are used to drive the fish from the seafloor and immobilise them in front of the nets. Concerns exist, however, that the electric fields may affect fishes outside the trawl track. Here, we address these concerns by measuring amplitude thresholds for behavioural responses and by comparing these response thresholds to simulated field strengths around fishing gear. Electroreceptive small-spotted catshark (Scyliorhinus canicula) and thornback ray (Raja clavata) as well as non-electroreceptive European seabass (Dicentrarchus labrax), turbot (Scophthalmus maximus), and common sole were, one at the time, placed in a ø2.5 m circular tank with seven, individually controlled, evenly spaced electrode pairs, spanning the diameter of the tank. Behavioural responses were assessed from camera recordings for different pulse amplitudes and for different fish positions relative to the stimulating electrodes. Electrical stimulation consisted of a Pulsed Bipolar Current at 45 Hz and 0.3 ms pulse width, similar to that used in commercial gears. Computer simulations of the electric field, verified with in situ measurements, were used to determine the field strength at the location of the animal. Thresholds for different species varied between 6.0 and 9.8 V m-1, with no significant difference between electroreceptive and non-electroreceptive species. The thresholds correspond to a distance of maximally 80 cm from the electrode arrays in simulated electric fields around commercial fishing gears. These findings suggest that electrical pulses as used in pulse trawling are unlikely to elicit a behavioural response outside the nets that surround the electrode arrays. [ABSTRACT FROM AUTHOR]

An 8-week feeding experiment was conducted on the juvenile turbot (Scophthalmus maximus) to evaluate the influence of yeast extract (YE) supplementation in the diet on growth performance, feed utilization, body composition, nutrient digestibility, intestinal histology, and antioxidant capacity. Four experimental diets were formulated with graded levels of yeast extract 0 (YE0), 1% (YE1), 3% (YE3), and 5% (YE5) and fed to turbots (initial body weight: 4.2 ± 0.1 g) with three replicates per diet and 200 fish in each replicate, respectively. The results showed that turbots fed with diets YE1 and YE3 displayed a significantly higher specific growth rate and protein efficiency rate than those fed with diets YE0 and YE5, while the feed conversion ratios in YE1 and YE3 groups were lower than those in YE0 and YE5. Fish fed with diets YE3 and YE5 showed higher body crude protein contents than those in groups YE0 and YE1. The highest apparent digestibility coefficients for dry matter and crude protein, digestive enzyme activities (trypsin, lipase, and amylase), and the height of the intestinal fold were observed in the YE3 group. YE3 treatment displayed a significantly higher superoxide dismutase (SOD) activity than the YE0 group, while the malondialdehyde (MDA) content in YE1 was significantly lower than those in YE0 and YE5. No significant difference was observed in serum physiological and biochemical parameters among all treatments. Overall, appropriate dietary supplementation of the yeast extract could improve the growth performance, digestibility, and antioxidant capacity of the juvenile turbot, and the recommended yeast extract level in the feed is 2.47%. [ABSTRACT FROM AUTHOR]

La capture de plusieurs spécimens de Lepidorhombus whiffiagonis et l’observation de deux spécimens de Scophthalmus maximus représentent les premiers signalements pour ces espèces aux îles Canaries. Il est vraisemblable que ces deux espèces sont présentes dans les eaux canariennes en raison de l’expansion naturelle de leurs aires de répartition depuis les zones environnantes. Ce travaille contribue également à la connaissance des caractéristiques morphologiques et méristiques des populations les plus méridionales de ces espèces tempérées-froides de l’Atlantique oriental. [ABSTRACT FROM AUTHOR]

Germ cell transplantation (GCT) is a promising biotechnology that enables the production of donor-derived gametes in surrogate recipients. It plays a crucial role in the protection of endangered species, the propagation of elite species with desired traits, and long-term preservation of genetic resources. This significance is particularly pronounced when GCT is synergistically employed with cryopreservation techniques. However, GCT often encounters challenges due to low colonization rates and, in some cases, complete loss of donor cells in recipients. Glial cell line-derived neurotrophic factor (GDNF) plays a pivotal role in sustaining the self-renewal of spermatogonial stem cells (SSCs) in mammals. Additionally, it has been shown to promote the proliferation of spermatogonia in vitro cultures in certain animal species. In turbot (Scophthalmus maximus), we found that the expressions of gdnf and gfrα1a were predominantly observed in spermatogonia rather than somatic cells, which differed from their expression patterns in mammals. The efficiency of exogenous spermatogonia transplantation in Japanese flounder (Paralichthys olivaceus) larvae could be substantially enhanced by incubating donor cells from turbot with 100 ng/ml GDNF prior to transplantation. This led to a noteworthy increase in the colonization rate, rising from 33%-50%–61.5%. Additionally, the addition of 20 ng/ml GDNF in cell medium could also promote the proliferation of turbot germ cells in vitro. These results demonstrated the gdnf in turbot testis expression characteristics and suggested that addition of GNDF could be an effective way to improve the GCT efficiency and promote the germ cells expansion during in vitro culture. • Expression patterns of gdnf and gfrα1a in turbot reveal preferential localization in spermatogonia, distinct from mammas. • GDNF incubation significantly enhances exogenous spermatogonia transplantation efficiency in Japanese flounder larvae. • GDNF addition boosts turbot germ cell proliferation in culture, hinting its potential to enhance germ cell expansion in vitro. [ABSTRACT FROM AUTHOR]

SOXE transcription factors, including SOX8, SOX9, and SOX10, regulate several developmental events, such as sex determination, chondrogenesis, and neurogenesis. This study systematically identified six SoxE subfamily genes from the turbot (Scophthalmus maximus) genome and transcriptome, including SmSox8a, SmSox8b, SmSox9a, SmSox9b, SmSox10a, and SmSox10b. The duplicates of three SOXE members revealed that SoxE subfamily genes in the turbot underwent significant expansion. Relatively conserved exon-intron structures and intron insertions were detected using genomic structural analysis. Besides, phylogenetic analysis supported the previous classification of the SoxE subfamily. Results of the expression profile revealed that turbot SoxE subfamily genes may be involved in different activities, such as neurogenesis and gonad development. These findings would assist in the understanding of fish SoxE gene subfamily activities and evolution. [ABSTRACT FROM AUTHOR]

Turbot Scophthalmus maximus is an important mariculture fish species with high economic value. However, the bacterial diseases caused by Vibrio anguillarum infection bring huge economic losses to the turbot aquaculture industry. To understand the immune response of the turbot against V. anguillarum infection and to explore novel immune-related genes, the transcriptome analysis of turbot spleen and gills were conducted after V. anguillarum infection. Differentially expressed genes (DEGs) were identified in spleen and gill of the turbot amounted to 17 261 and 16 436, respectively. A large number of immune-related DEGs were enriched in cytokine-cytokine receptor interaction signaling pathway, and the others by the kyoto encyclopedia of genes and genomes (KEGG) enrichment. The gene ontology (GO) classification analysis revealed that V. anguillarum infection had the greatest effect on biological processes and cellular components. Twelve immune-related DEGs were identified in the spleen (cstl.1, egfl6, lamb21, v2rx4, calcr, and gpr78a) and gills (ghra, sh3gl2a, cst12, inhbaa, cxcl8, and il-1b) by heat map. The protein-protein interaction (PPI) networks were constructed to analyze the immune mechanism. The results demonstrate that the maturation and antigen processing of major histocompatibility complex (MHC) class II molecule, and calcitonin- or adrenomedullin-regulated physiological activity were important events in the immunity of turbot against V. anguillarum infection. In the gills, the protein interactions in TGF-β signaling pathway, production of inflammatory factors, and endocytosis regulation were most significant. Our research laid a foundation for discovering novel immune-related genes and enriching the knowledge of immune mechanisms of turbot against V. anguillarum infection. [ABSTRACT FROM AUTHOR]

Carbohydrates are a common and economical energy source in animal feeds. However, most fish show a persistent postprandial hyperglycemia after intake of a high-carbohydrate diet. Unfortunately, the mechanism of glucose metabolism in fish is still unclear. In the present study, tiger puffer (Takifugu rubripes) and turbot (Scophthalmus maximus) were intraperitoneally injected or orally administered with glucose or fructose (500 mg/kg body weight) to evaluate the ability of fish to utilize carbohydrates. Afterwards, serum glucose, fructose, pyruvate, insulin levels, and acute hypoxia tolerance were measured. Our results showed increased serum glucose level and then decreased post intraperitoneal injection with glucose, and reached a peak after 0.5 hours in turbot and 1 hour in tiger puffer. Tiger puffer had significantly lower liver glycogen, serum glucose, fructose, pyruvate, and insulin contents than turbot. Glucose and fructose only induced insulin secretion in turbot, but did not change serum insulin level in tiger puffer. Glucose was a stronger stimulator of insulin than fructose in the two marine species. Both intraperitoneal injection and oral fructose intake increased serum glucose level, while intraperitoneal or oral glucose also increased serum fructose level. Intraperitoneal injection of glucose promoted absorption and utilization of glucose in the blood more effectively than oral glucose intake. In addition, turbot and tiger puffer were intolerant to acute hypoxia, whereas supplementation with glucose or fructose improved hypoxia tolerance in the two marine fishes by activating anaerobic glycolysis. Taken together, our results provide important scientific information for understanding the mechanism for glucose and fructose utilization and improving hypoxia tolerance in fish. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effects of imbalanced dietary BCAAs, especially Leu, on the growth and BCAA metabolism in turbot. A control diet was formulated by keeping optimum levels of Leu, Ile and Val. Four experimental diets were prepared by removing supplemental crystalline Leu (deficiency) or supplementing double the amount of Leu, Ile or Val (excess) in the control diet. The growth was not significantly decreased by an excess of Leu, Ile or Val. Fish fed an excess of any particular BCAA significantly increased its postprandial (2 and 6 h) concentration in the plasma, muscles, and liver, but did not decrease the other two BCAA concentrations. The expression of intestinal b0at1 was down-regulated by excessive dietary Leu, Ile or Val. For BCAA catabolism, the mRNA levels of bcat2 in the muscles as well as bckdha and bckdhb in the livers of the Leu-deficient group were the lowest among all the groups, but were up-regulated by excess dietary Leu, Ile or Val. In conclusion, in terms of growth, turbot had high plasticity to an excess of any particular BCAA. Meanwhile, the antagonistic effect caused by an excess of one BCAA were reflected in intestinal amino acid absorption and BCAA catabolism. [ABSTRACT FROM AUTHOR]

Long non-coding RNAs (lncRNAs) play crucial roles in a variety of biological processes, including stress response. However, the number, characteristics and stress-related expression of lncRNAs in turbot are still largely unknown. In this study, a total of 12,999 lncRNAs were identified at the genome-wide level of turbot for the first time using 24 RNA-seq datasets. Sequence characteristic analyses of transcripts showed that lncRNA transcripts were shorter in average length, lower in average GC content and in average expression level as compared to the coding genes. Expression pattern analyses of lncRNAs in 12 distinct tissues showed that lncRNAs, especially lincRNA, exhibited stronger tissue-specific expression than coding genes. Moreover, 612, 1351, 1060, 875, 420 and 1689 differentially expressed (DE) lncRNAs under Vibrio anguillarum, Enteromyxum scophthalmi, and Megalocytivirus infection and heat, oxygen, and salinity stress conditions were identified, respectively. Among them, 151 and 62 lncRNAs showed differential expression under various abiotic and biotic stresses, respectively, and 11 lncRNAs differentially expressed under both abiotic and biotic stresses were selected as comprehensive stress-responsive lncRNA candidates. Furthermore, expression pattern analysis and qPCR validation both verified the comprehensive stress-responsive functions of these 11 lncRNAs. In addition, 497 significantly co-expressed target genes (correlation coefficient (R) > 0.7 and q-value < 0.05) for these 11 comprehensive stress-responsive lncRNA candidates were identified. Finally, GO and KEGG enrichment analyses indicated that these target genes were enriched mainly in molecular function, such as cytokine activity and active transmembrane transporter activity, in biological processes, such as response to stimulus and immune response, and in pathways, such as protein families: signaling and cellular processes, transporters and metabolism. These findings not only provide valuable reference resources for further research on the molecular basis and function of lncRNAs in turbot but also help to accelerate the progress of molecularly selective breeding of stress-resistant turbot strains or varieties. [ABSTRACT FROM AUTHOR]

Pheromones play a vital role in regulating fish behavior, including reproduction, aggregation, hazard recognition and food location. To gain a better understanding of chemical communication in fish produced by density changes, this study analyzed the metabolites released by turbot (Scophthalmus maximus) under different stocking densities. The experiment was conducted at low (LD: 3.01 kg/m2), medium (MD: 6.62 kg/m2) and high (HD: 10.84 kg/m2) densities for 15 days. High-throughput non-targeted metabolomics (LC-MS/MS) was used to identify variations in metabolites released into the aquatic environment by turbot at different densities. Results showed that 29 and 47 metabolites were significantly upregulated in the MD and HD groups, respectively, compared with the LD group. Among them, hexadecanedioic acid, xanthine, phenethylamine, proline and styrene were significantly upregulated in the MD vs. LD, HD vs. MD and HD vs. LD. The VIP diagram of OPLS-DA alignment showed that phenethylamine was the most important metabolite shared by MD vs. LD, HD vs. MD and HD vs. LD. Key gene changes in the GH/IGF-1 signaling pathway, HPI axis of turbot were studied using qRT-PCR for density treatment. The results demonstrated that the expression of GH, GHR and IGF-1 was significantly lower, while the expression of CRH and ACTH was higher in the HD group. Additionally, plasma levels of cortisol, glucose, triglycerides and T3 were also highest in the HD group compared with the LD and MD groups. Phenylethylamine concentration was positively correlated with the HPI axis and negatively correlated with the GH/IGF-1 signaling pathway. To investigate the impact of phenethylamine accumulation on turbot, an acute treatment experiment with phenethylamine was set up. Its concentration in the aquatic environment was set at 0 (CON), 10−7 (LP) and 10−5 (HP) mol/L via exogenous addition, and turbot were exposed to these environments for 2 days. There was a high degree of concordance between the GH/IGF-1 signaling pathway (GH, GHR, IGF-1), HPI axis (CRH, ACTH) and plasma physiological changes (cortisol, glucose, triglycerides, T3) in the phenethylamine-treated group and the density-treated group. Therefore, accumulation of phenethylamine with increasing stocking density may be a potential cause of density stress. Phenylethylamine has a dose-dependent and trace effect as a pheromone. [ABSTRACT FROM AUTHOR]

The present study examined the genetic diversity and spatial distribution of turbot (Scophthalmus maximus), an economically important species on the Bulgarian Black Sea coast. Maximum entropy (MaxEnt) modeling software Version 3.4.4. was utilized to develop a habitat suitability model for S. maximus in the Bulgarian Black Sea region. Data collected via demersal and pelagic surveys and genetic sampling from 2017 to 2021 were utilized to link species occurrence localities with selected abiotic factors. Our findings showed that the species' habitat preferences are strongly influenced by temperature and dissolved oxygen, and projections based on simplified climatic scenarios indicated potential distribution shifts and a substantial reduction in reproduction habitats in the northern region. The assessment of genetic diversity was based on mtDNA COIII sequencing; MtDNA revealed a low level of polymorphism in all analyzed populations. The extensive fishing pressure may have increased the likelihood of genetic and population bottlenecks and a consequent decline in genetic diversity in the Shabla, Nesebar, and Tsarevo populations. The Tajima's D values for the latter indicated that turbot underwent a bottleneck followed by rapid population expansion. Our findings are essential for the conservation and effective management of S. maximus stocks in the region. [ABSTRACT FROM AUTHOR]

Turbot aquaculture production is an important economic activity in several countries around the world; nonetheless, the incidence of diseases, such furunculosis, caused by the etiological agent A. salmonicida subsp. salmonicida, is responsible for important losses to this industry worldwide. Given this perspective, this study aimed to evaluate early immune responses in turbot (S. maximus L.) following infection with A. salmonicida subsp. salmonicida. For this, 72 fish were individually weighed and randomly distributed into 6 tanks in a circulating seawater system. For the bacterial challenge, half of the individuals (3 tanks with 36 individuals) were infected using a peritoneal injection with the bacterial suspension, while the other half of individuals were injected with PBS and kept as a control group. Several factors linked to the innate immune response were studied, including not only haematological (white blood cells, red blood cells, haematocrit, haemoglobin, mean corpuscular volume, mean cell haemoglobin, mean corpuscular haemoglobin concentration, neutrophils, monocytes, lymphocytes, thrombocytes) and oxidative stress parameters, but also the analyses of the expression of 13 key immune-related genes (tnf-α, il-1β, il-8, pparα-1, acox1, tgf-β1, nf-kB p65, srebp-1, il-10, c3, cpt1a, pcna, il-22). No significant differences were recorded in blood or innate humoral parameters (lysozyme, anti-protease, peroxidase) at the selected sampling points. There was neither any evidence of significant changes in the activity levels of the oxidative stress indicators (catalase, glutathione S-transferase, lipid peroxidation, superoxide dismutase). In contrast, pro-inflammatory (tnf-α, il-1β), anti-inflammatory (il-10), and innate immune-related genes (c3) were up-regulated, while another gene linked with the lipid metabolism (acox1) was down-regulated. The results showed new insights about early responses of turbot following infection with A. salmonicida subsp. salmonicida. [ABSTRACT FROM AUTHOR]

The aim of this research was to evaluate the health status of the Scophthalmus maeoticus (Pallas, 1814) population from the Romanian marine area in 2016–2019, by identifying and investigating information about bacterial and constitutional diseases, establishing the influence of these bacterioses on the researched populations, and highlighting the main biological disorders (reproduction, growth, and feeding) that manifested in the analyzed fish. The bacterial diseases reported in S. maeoticus (Pallas, 1814) populations were caused by pathogens from the genera Vibrio, Aeromonas, and Pseudomonas. Numerous skin diseases, especially various types of "wounds", lesions of bony tubercles, and tissue lesions may be the subsequent cause of neoplasms, as a result of fishing gear manipulations. The appearance of significant changes in the prevalence of neoplasia on the Romanian Black Sea coast can be considered an indicator of chronic stress (anthropogenic impact), rather than acute (environmental impact), and we suggest that the species could be used as a biological indicator of changes that may occur in the habitat in which it lives. In terms of future research directions, a combined analysis of the population structure, morphology and diseases determined in S. maeoticus populations, with a structural analysis of the habitat and bacteria contamination degree would be useful; this monitoring should be carried out regularly, to reveal changes in the Black Sea ecosystem, and to propose possible recommendations and protective measures. [ABSTRACT FROM AUTHOR]

In this study, we determined the biological characteristics and indices of abundance and biomass of two demersal species, turbot and thornback ray, through a scientific trawl survey of Bulgarian Black Sea waters in the autumn of 2020. Turbot is among the most valuable fish species in the Black Sea, and thornback ray is a sensitive cartilaginous species with a significantly declining abundance throughout the Mediterranean region. The stock biomass of turbot was estimated at 1467.6 tons, with a relative abundance of 896,922 individuals, and those of the thornback ray were 1187.9 tons and 519,606 individuals, respectively. Mean turbot abundance, interpolated into 0.5° latitude/longitude grid cells, ranged between 52 and 120 ind·km−2, with a mean biomass of 78.26–238.31 kg·km−2, and for the thornback ray, these indices were within the limits of 0–107 ind·km−2 and 0–219 kg·km−2. The distribution of the different length classes of the two fish species by depth layer was analyzed. Length–weight relationships were estimated based on combined samples of both sexes and separately for female and male individuals, allowing a better understanding of growth patterns. [ABSTRACT FROM AUTHOR]

Ovarian fluid is essential for successful fertilization by maintaining the viability, motility, and velocity of sperm. The organic compounds and inorganic ions in ovarian fluid significantly influence spermatozoa's motility, velocity, and longevity. However, the effect of ovarian fluid on sperm performance is limited in teleost fish. In this study, the effect of ovarian fluid on sperm performance and its components in external fertilization species (Scophthalmus maximus , turbot) and internal fertilization species (Sebastes schlegelii , black rockfish) was investigated using computer-assisted sperm analysis, high-performance liquid chromatography, and metabolome analysis. The ovarian fluid had a distinct and species-specific effect on both species. In the black rockfish, the ovarian fluid from turbot significantly increased sperm motility (74.07% ± 4.09%), as well as VCL (45 ± 1.67 μm/s), VAP (40.17 ± 1.6 μm/s), and VSL (36.67 ± 1.86 μm/s), and longevity (352 ± 11.31 min) (P < 0.05). In the turbot, only the longevity (71.33 ± 5.69 min) and fertilization rate (65.27% ± 11.59%) showed significantly improvement (P < 0.05). The ovarian fluid was rich in organic compounds, suggesting enrichment in the glycolysis/gluconeogenesis pathways. The results suggest that glycometabolism plays a crucial role in improving sperm performance in teleost with internal fertilization. Thus, incorporating ovarian fluid into the sperm activation medium can enhance artificial fertilization in fish breeding. • Ovarian fluid has different effect in turbot and black rockfish. • Ovarian fluid enhanced sperm motility in black rockfish. • Ovarian fluid significantly prolonged sperm longevity in turbot and black rockfish. • Ovarian fluid may provide energy for sperm survival and extended longevity. [ABSTRACT FROM AUTHOR]

The development and maturation of sperm entails intricate metabolic processes involving water molecules, amino acids, hormones, and various substances. Among these processes, the role of aquaporins (aqps) in the testis is crucial. Turbot (Scophthalmus maximus) is a significant marine flatfish species in China; however, natural egg laying in females is not feasible under cultured conditions. Consequently, artificial insemination becomes necessary, requiring the retrieval of sperm and eggs through artificial methods. In this study, we combined genomic, transcriptomics, RT-qPCR, computer-assisted sperm analysis (CASA), and immunohistochemistry to investigate the involvement of the aqp family in spermatogenesis in turbot. Through genomic data analysis, we identified 16 aqps genes dispersed across 13 chromosomes, each exhibiting the characteristic major intrinsic protein (MIP) domain associated with AQPs. The results from RNA-seq and RT-qPCR analysis revealed prominent expression of aqp4, 10, and 12 during the proliferative stage, whereas aqp1 showed primary expression during the mature stage. aqp11 displayed high expression levels during both MSII and MSV stages, potentially contributing significantly to the proliferation and maturation of male germ cells. Conversely, aqp8 showed elevated expression levels during the MSIII, MSIII-IV, and MSIV stages, suggesting its direct involvement in spermiogenesis. Immunohistochemical analysis unveiled the predominant localization of AQP1 protein in male germ cells rather than Sertoli cells, specifically concentrated in the head of sperm within cysts. Furthermore, a noteworthy decline in sperm motility was observed when sperm were subjected to treatment with either the AQP1-specific inhibitor (HgCl2) or the AQP1 antibody. However, no direct correlation was found between the expression of Smaqp1 and sperm quality. Overall, these findings provide new insights into the involvement of aqps in teleost spermatogenesis. Moreover, they hold potential for improving techniques related to sperm activation and cryopreservation, offering valuable knowledge for future advancements in this field. [ABSTRACT FROM AUTHOR]

Simple Summary: The in vitro antiprotozoal activity of Hibiscus sabdariffa ethanolic extract was evaluated on the ciliate parasite Philasterides dicentrarchi, which causes severe losses in turbot aquaculture. Our results showed that H. sabdariffa extract had successfully inhibited the parasite population growth rate (IC50 = 1.57 mg mL−1), and caused significant changes in the activity of antioxidant enzymes (LOEC = 0.22 mg mL−1), especially glutathione peroxidase, total glutathione, and catalase. The activity of proteases (virulence factors) was also inhibited (IC50 = 0.76 mg mL−1), and the gene expression of catepsin 90 and leishmanolysin proteases was downregulated. Organic acids and phenolic phytochemicals in hibiscus extract are potentially responsible for the antiprotozoal bioactivity herein determined. Therefore, H. sabdariffa extract can be a promising disease-control alternative against the ciliate proliferation, cellular defense mechanisms, and pathogenicity. Philasterides dicentrarchi is an histophagous parasite that infects flatfish, namely turbot (Scophthalmus maximus), and cause significant losses in aquaculture units. The available measures for P. dicentrarchi control have limited efficiency, and some cause harm to fish. Hence, sustainable and natural control strategies are urgently needed. This study evaluated the in vitro bioactivity of the ethanol extract of Hibiscus sabdariffa calyces on P. dicentrarchi population growth rate (PGR), oxidative stress biomarkers (glutathione-S-transferases (GST), glutathione reductase (GR), glutathione peroxidase (GPx), total glutathione (TG) and catalase (CAT), neurotoxicity (acetylcholinesterase, AChE), activity and gene expression of proteases as major virulence factors. H. sabdariffa extract inhibited parasite PGR (IC50 = 1.57 mg mL−1), and caused significant changes in the activity of antioxidant enzymes (LOEC = 0.22 mg mL−1), especially GPx, TG, and CAT. The activity of proteases was also severely inhibited (IC50 = 0.76 mg mL−1), and gene expression of catepsin 90 and leishmanolysin proteases was downregulated. Organic acids and phenolic phytochemicals in hibiscus extract are potentially responsible for the antiprotozoal bioactivity herein determined. Therefore, H. sabdariffa extract can be a promising disease-control alternative against the ciliate proliferation, cellular defense mechanisms and pathogenicity. Still, its applicability in aquaculture settings, and potential effects on farmed fish, should be further elucidated. [ABSTRACT FROM AUTHOR]

Manganese superoxide dismutase (MnSOD) and catalase (CAT) could eliminate reactive oxygen species (ROS) and maintain the reduction-oxidation balance in cells. This study aimed to investigate their functions in turbot (Scophthalmus maximus) response to the Vibro anguillarum challenge. SmMnSOD, the full-length liver cDNA of MnSOD from S. maximus, was cloned by fast amplification of cDNA ends (RACE). Sequencing of nucleotides indicated that the SmMnSOD cDNA was 1267 base pairs with a 684-base-pair open reading frame, encoding a 228 amino acid protein with 28 amino acid residues. The SmMnSOD sequence contains MnSOD signatures (DVWEHAYY) and probable N-glycosylation sites (NVT, NHT, and NLS). The deduced sequence of SmMnSOD revealed sequence homology between 85.3% and 92.9% with those of other species. A phylogenetic study found that SmMnSOD clustered with other fish MnSOD, indicating that SmMnSOD was a member of the MnSOD family. The SmMnSOD transcript was discovered by qRT-PCR in the gill, stomach, head-kidney, muscle, liver, intestine, and heart of S. maximus, with the highest expression in the liver. Upon intervention by V. anguillarum, the liver and head kidney transcript levels of SmMnSOD were up-regulated at 12 and 48 h, whereas the temporal expression profiles of the CAT transcript increased at 6 and 24 h. As the pathogenic bacterial stress processing was prolonged to 72 h, the liver and head kidney transcript levels of SmMnSOD and CAT decreased gradually. Thus, SmMnSOD was triggered and may be related to S. maximus' immunological responses against V. anguillarum. [ABSTRACT FROM AUTHOR]

High-quality eggs are essential for the sustainability of commercial aquaculture production. Melatonin is a potent candidate for regulating the growth and maturation of oocytes. Therefore, research on the effect of melatonin on marine fish oocytes in vitro has been conducted. The present study successfully established a culture system of turbot (Scophthalmus maximus) oocytes in vitro and investigated the effect of melatonin on oocyte meiotic maturation, antioxidant capacity, and the expression of apoptosis-related genes. The cultures showed that turbot Scophthalmus maximus late-vitellogenic denuded oocytes, with diameters of 0.5–0.7 mm, had a low spontaneous maturation rate and exhibited a sensitive response to 17α, 20β-dihydroxyprogesterone (DHP) treatment in vitro. Melatonin increased by four times the rate of oocyte germinal vesicle breakdown (GVBD) in a concentration- and time-dependent manner. The mRNA of melatonin receptor 1 (mtnr1) was significantly upregulated in the oocyte and follicle after treatment with melatonin (4.3 × 10−9 M) for 24 h in vitro, whereas melatonin receptor 2 (mtnr2) and melatonin receptor 3 (mtnr3) remained unchanged. In addition, melatonin significantly increased the activities of catalase, glutathione peroxidase, and superoxide dismutase, as well as the levels of glutathione, while decreasing the levels of malondialdehyde and reactive oxygen species (ROS) levels in turbot oocytes and follicles cultures in vitro. p53, caspase3, and bax mRNAs were significantly downregulated in oocytes and follicles, whereas bcl2 mRNAs were significantly upregulated. In conclusion, the use of turbot late-vitellogenesis oocytes (0.5–0.7 mm) is suitable for establishing a culture system in vitro. Melatonin promotes oocyte meiotic maturation and antioxidative capacity and inhibits apoptosis via the p53-bax-bcl2 and caspase-dependent pathways, which have important potential to improve the maturation and quality of oocytes. [ABSTRACT FROM AUTHOR]

Simple Summary: In some fish farming practices, cholesterol has been used as a feed additive for growth stimulation. Therefore, it is important to increase our knowledge and experience about dietary cholesterol effects on fish. This study provides useful information for the application of cholesterol in fish diets by analyzing the muscle lipidomics changes in turbot and tiger puffer in response to dietary cholesterol supplementation. Exogenous cholesterol has been supplemented into aqua-feeds due to the reduced proportions of fishmeal and fish oil. This study aimed to investigate the effects of dietary cholesterol supplementation on the muscle lipidomics of two marine fish species, turbot and tiger puffer. A 70-day feeding trial was conducted, where two low-fishmeal diets supplemented with 0 or 1% cholesterol were used. The lipidomic analysis with targeted tandem mass spectrometry showed that, in turbot, a total of 49 individual lipids exhibited significant differences in their abundance in response to dietary cholesterol, whereas the number was 30 for tiger puffer. Dietary cholesterol up-regulated the abundance of cholesterol and cholesterol ester in both species. In turbot, the dietary cholesterol also increased the abundance of triacylglycerol and acylcarnitine, whereas in tiger puffer, it primarily regulated the abundance of phospholipids and BMP. This was the first time the responses of marine fish muscle lipidomics to dietary cholesterol supplementation have been investigated. [ABSTRACT FROM AUTHOR]

In this study, the exopolysaccharide (EPS) from Lactiplantibacillus plantarum (HMX2) was isolated from Chinese Northeast Sauerkraut. Its effects on juvenile turbot were investigated by adding different concentrations of HMX2-EPS (C: 0 mg/kg, H1: 100 mg/kg, H2: 500 mg/kg) to the feed. Compared with the control group, HMX2-EPS significantly improved the growth performance of juvenile turbot. The activities of antioxidant enzymes, digestive enzymes, and immune-related enzymes were significantly increased. HMX2-EPS could also increase the secretion of inflammatory factors and enhance the immune response of turbot by regulating the IFN signal transduction pathway and exhibit stronger survival rates after the A. hydrophila challenge. Moreover, HMX2-EPS could improve the diversity of intestinal microbiota in juvenile fish, increase the abundance of potential probiotics, and reduce the abundance of pathogenic bacteria. The function of gut microbes in metabolism and the immune system could also be improved. All results showed better effects with high concentrations of HMX2-EPS. These results indicated that HMX2-EPS supplementation in the diet could promote growth, improve antioxidant activity, digestive capacity, and immunity capacity, and actively regulate the intestinal microbiota of juvenile turbot. In conclusion, this study might provide basic technical and scientific support for the application of L. plantarum in aquatic feed. [ABSTRACT FROM AUTHOR]

The health of aquatic organisms can be affected due to anthropogenic activities and limited actions to reduce the pollution of the Black Sea. The accumulation of organic pollutants (OPs) in the aquatic environment occurs in water, sediment, and then biota. The turbot (Scophthalmus maeoticus) is a benthic fish of commercial interest scarcely studied in the Black Sea region, and none of the studies researched OP concentrations in its main tissues. In this paper, polycyclic aromatic hydrocarbons (PAHs) and POPs, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were determined in water, sediment, and turbot muscles, gills, gonads, and livers, to research their accumulation level. The determinations were made with gas chromatography on turbots sampled in 2021 from the Romanian Black Sea waters. OCPs—p,p'DDT and its metabolites p,p'DDE, p,p'DDD—are dominant in the turbot tissues. From PAHs, benzo(g,h, i)perylene was the dominant compound, while for PCBs it was PCB 52. The OPs' presence in the wild turbot is due to river input, dredging and coastal rehabilitation works, industrial activities and contaminated food and poses a risk to human health due to the exceeding maximum allowable concentration for human consumption in Romania and the European Union. [ABSTRACT FROM AUTHOR]

Fish reproduction is closely related to the regulation of the brain and liver, making it essential to identify the factors that control this process. The turbot (Scophthalmus maximus) is an economically significant species that has been successfully breeding through industrial aquaculture. Investigation of factors into the involvement of gonadal development is crucial for artificial breeding. In this study, a new insulin-like growth factor 3 igf3 gene was cloned and characterized. Additionally, all three types of turbot IGFs contain a distinct IGF domain, with IGF3 and IGF2 being grouped with other teleosts, demonstrating a closely related genetic relationship. The expression analysis showed that igf3 mRNA is predominantly expressed in the gonad and brain (specifically in the pituitary and hypothalamus), suggesting its effects at multiple levels in the brain–pituitary–gonadal axis. Furthermore, the mRNA levels of igfs during gonadal development were examined. In the gonad and liver of female turbots, the expression levels of igfs mRNA significantly increased from stage II to VI during the process of oogenesis, including maturation and degeneration. In the testis and liver of male turbots, igf3 mRNA maintained high expression levels during the proliferation of spermatogonia at stages II and III. In addition, the highest levels of igf1 and igf2 were observed at the beginning of spermatogenesis and during sperm production at stages V and VI. All the results suggest that the IGFs were closely related to the gonadal development in turbot and improve a better understanding of the IGF system in the regulation of gonadal development in teleost. [ABSTRACT FROM AUTHOR]

Simple Summary: There have been reports on alternate feeding between diets based on different lipid sources, but how the intestinal microbiota of fish responds to alternate feeding strategies and its relevant roles in the host's health have not been reported. The present study provides novel results in this area. The main objective of the study was to assess how the intestinal microbiota of fish responds to alternate feeding between diets based on different lipid sources. Foremost, the juvenile turbot accepted alternate feeding between diets based on different lipid sources with no negative effects on survival or growth performance. Additionally, novel results were observed regarding the different bacterial compositions, microbial co-occurrence networks, and functional predictions among the different alternating feeding strategies. The results of this study indicate that a more comprehensive evaluation should be conducted from the perspective of intestinal microorganisms when a new feeding strategy is applied in aquaculture practices. These results will contribute to the nutritional regulation of aquatic animals from the perspective of microorganisms. A nine-week feeding trial was conducted to investigate changes in the intestinal microbiota of turbot in response to alternate feeding between terrestrially sourced oil (TSO)- and fish oil (FO)-based diets. The following three feeding strategies were designed: (1) continuous feeding with the FO-based diet (FO group); (2) weekly alternate feeding between soybean oil (SO)- and FO-based diets (SO/FO group); and (3) weekly alternate feeding between beef tallow (BT)- and FO-based diets (BT/FO group). An intestinal bacterial community analysis showed that alternate feeding reshaped the intestinal microbial composition. Higher species richness and diversity of the intestinal microbiota were observed in the alternate-feeding groups. A PCoA analysis showed that the samples clustered separately according to the feeding strategy, and among the three groups, the SO/FO group clustered relatively closer to the BT/FO group. The alternate feeding significantly decreased the abundance of Mycoplasma and selectively enriched specific microorganisms, including short-chain fatty acid (SCFA)-producing bacteria, digestive bacteria (Corynebacterium and Sphingomonas), and several potential pathogens (Desulfovibrio and Mycobacterium). Alternate feeding may maintain the intestinal microbiota balance by improving the connectivity of the ecological network and increasing the competitive interactions within the ecological network. The alternate feeding significantly upregulated the KEGG pathways of fatty acid and lipid metabolism, glycan biosynthesis, and amino acid metabolism in the intestinal microbiota. Meanwhile, the upregulation of the KEGG pathway of lipopolysaccharide biosynthesis indicates a potential risk for intestinal health. In conclusion, short-term alternate feeding between dietary lipid sources reshapes the intestinal microecology of the juvenile turbot, possibly resulting in both positive and negative effects. [ABSTRACT FROM AUTHOR]

Circular economy driven feed ingredients and emerging protein sources, such as insects and microbial meals, has the potential to partially replace fishmeal in diets of high-trophic fish. Even though growth and feed performance are often unaffected at low inclusion levels, the metabolic effects are unknown. This study examined the metabolic response of juvenile turbot (Scophthalmus maximus) to diets with graded fishmeal replacement with plant, animal, and emerging protein sources (PLANT, PAP, and MIX) in comparison to a commercial-like diet (CTRL). A 1H-nuclear magnetic resonance (NMR) spectroscopy was used to assess the metabolic profiles of muscle and liver tissue after feeding the fish the experimental diets for 16 weeks. The comparative approach revealed a decrease in metabolites that are associated with energy deficiency in both tissues of fish fed with fishmeal-reduced diets compared to the commercial-like diet (CTRL). Since growth and feeding performance were unaffected, the observed metabolic response suggests that the balanced feed formulations, especially at lower fishmeal replacement levels, have the potential for industry application. [ABSTRACT FROM AUTHOR]

Biosorption successfully remediates saline water contaminated with legacy contaminants, but its effects on the health of marine organisms remain unclear. Therefore, our aim was to address this knowledge gap with data on the accumulation ability, as well as the cytogenetic and biochemical effects in turbot (Scophthalmus maximus). To this end, we exposed turbot for seven days to a mixture of remediated metals (Rem treatments: Cd, Hg, and Pb), with and without the presence of nanoparticles (NP), and compared them with the maximum allowable concentrations (MAC treatment) for effluent discharges. We determined the metal accumulation in the blood and kidney and evaluated haematological changes (red blood cell count, haemoglobin, and mean cell haemoglobin (MCH)) and genotoxicity (erythrocytic nuclear abnormalities assay) in the blood. The results showed that remediation with non-living macroalgae significantly reduced the metallic blood and kidney burdens in the Rem treatments. Furthermore, no genotoxic potential occurred in the Rem and MAC treatments in parallel with the reduction in MCH levels in the Rem treatments, which would reflect hematopoietic disturbances in the MAC. Our results validate biosorption remediation as we achieved a considerable reduction in metal loads while maintaining the health status of fish, highlighting the importance of testing water remediation methods in the biota. [ABSTRACT FROM AUTHOR]

A 12-week feeding trial was conducted to investigate the effect of the same fishmeal protein level replaced by black soldier fly larvae (Hermetia illucens) meal (BSFL) with different lipid contents on the growth performance and intestinal health of juvenile turbot (Scophthalmus maximus L.) (initial body weight 12.64 g). Three isonitrogenous and isolipidic diets were formulated: fish meal-based diet (FM), diets DF and FF, in which 14% fish meal protein of the FM diet was replaced by defatted and full-fat BSFL, respectively. There were no significant differences in growth performance, intestinal morphology, and mucosal barrier function between the DF and the FM group. However, diet FF markedly reduced the growth performance, intestinal perimeter ratio, and the gene expression of anti-inflammatory cytokine TGF-β (P < 0.05). Compared to group FF, the communities of intestinal microbiota in group DF were more similar to group FM. Moreover, diet DF decreased the abundance of some potential pathogenic bacteria and enriched the potential probiotics, such as Bacillus. Diet FF obviously altered the composition of intestinal microbiota and increased the abundance of some potential pathogenic bacteria. These results suggested that the application of defatted BSFL showed more positive effects on fish growth and intestinal health than the full-fat BSFL, and the intestinal microbiota was closely involved in these effects. [ABSTRACT FROM AUTHOR]

Lepeophtheirus salmonis was collected from the Atlantic salmon, Salmo salar, in Turkey. It is known as the salmon louse. It was obtained from fish samples that were farmed in Norway and imported to Turkey. Although it has not been proven that the salmon louse carries zoonotic or any pathogens, attention should be paid to biosecurity measures and hygiene rules in product trade among countries. This study demonstrates that the fish louse, even dead, travels between countries. In addition, Lepeophtheirus europaensis was collected from the turbot and the brill during the project to monitor demersal fish from Turkey. L. europaensis was diagnosed on wild fish in this study; it is important to know the diversity of parasites in terms of taking precautions against possible future diseases, since the farming of these fish is carried out in Turkey. L. europaensis was also reported for the first time on turbot and brill in Turkey. [ABSTRACT FROM AUTHOR]

Heat shock proteins 70 (HSP70s) are known to play essential roles in organisms' response mechanisms to various environmental stresses. However, no systematic identification and functional analysis has been conducted for HSP70s in the turbot (Scophthalmus maximus), a commercially important worldwide flatfish. Herein, 16 HSP70 genes unevenly distributed on nine chromosomes were identified in the turbot at the genome-wide level. Analyses of gene structure, motif composition, and phylogenetic relationships provided valuable data on the HSP70s regarding their evolution, classification, and functional diversity. Expression profiles of the HSP70 genes under five different stresses were investigated by examining multiple RNA-seq datasets. Results showed that 10, 6, 8, 10, and 9 HSP70 genes showed significantly up- or downregulated expression after heat-induced, salinity-induced, and Enteromyxum scophthalmi, Vibrio anguillarum, and Megalocytivirus infection-induced stress, respectively. Among them, hsp70 (hspa1a), hspa1b, and hspa5 showed significant responses to each kind of induced stress, and qPCR analyses further validated their involvement in comprehensive anti-stress, indicating their involvement in organisms' anti-stress mechanisms. These findings not only provide new insights into the biological function of HSP70s in turbot adapting to various environmental stresses, but also contribute to the development of molecular-based selective breeding programs for the production of stress-resistant turbot strains in the aquaculture industry. [ABSTRACT FROM AUTHOR]

BACKGROUND: Parvalbumin (PV) can be subdivided into two phylogenetic lineages, αPV and βPV. The bony fish βPV is considered a major fish allergen. However, there is no available report on the immunological property and epitope mapping of bony fish αPV. RESULTS: To characterize the allergenic property of bony fish αPV and investigate the difference in allergenic property of bony fish αPV and βPV, turbot (Scophthalmus maximus) αPV and βPV were identified by mass spectrometry and were expressed in Escherichia coli system in this study. Spectra analysis and three‐dimensional (3D) modeling showed the similar structure between αPV and βPV. However, αPV exhibited lower immunoglobulin E/immunoglobulin G (IgE/IgG) binding capacity than βPV. Three identified βPV epitopes possessed higher IgE reactivity and more hydrophobic residues than three identified αPV epitopes. In addition, less similarity in sequence homology of αPV epitopes was observed with allergen sequences in database. CONCLUSION: These finding expanded information on fish PV epitopes and substantiated the difference in allergenicity and epitope mapping between fish αPV and βPV, which will improve the epitope‐based detection tools of PV and diagnostic of PV induced fish allergy. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Probiotic bacteria are a recognized alternative to classical methods of disease prophylaxis and therapy. We tested the effects of their application on the immune reaction in juvenile turbot. To prevent digestion of the probiotics, rectal administration was applied to maximise colonization, by-passing digestion in the stomach. The application of Psychrobacter nivimaris and Psychrobacter faecalis showed beneficial effects on the inflammatory response and disease resistance after infection with the common pathogen Tenacibaculum maritimum. Treatment with P. nivimaris and P. faecalis resulted in 0% and 8% mortalities post-infection, while in the treatment control, an elevated mortality of 20% was observed. In the challenge controls (no infection), no mortalities were observed during the entire experimental period. After an experimental infection, mRNA expression of selected immune markers (mhc II α, il-1β, tcr, tgf β and tnf α) were determined by RT-QPCR at 0, 1 and 5 days post-infection (dpi). At 0 dpi, gene expression was comparable between the treatments and the treatment control, suggesting that probiotics did not act via immune stimulation of the host. At 1 dpi, all genes were up-regulated in the treatment control but not in the probiotic groups, indicating that the infection in probiotic-treated fish developed at a less severe level. At 5 dpi, mRNA expression returned to baseline levels. As a conclusion, the native probiotic candidates P. nivimaris and P. faecalis improved survival, whereas, in the control, mortality increased and expression of the immune markers was up-regulated post infection. This highlights a potential application of P. nivimaris and P. faecalis in disease prophylaxis, but further research is needed. [ABSTRACT FROM AUTHOR]

After more than four decades of production in the European Union, turbot (Psetta maxima) farming is a mature sector with a moderate growth trend (2.74% in 2020). Although up to seven countries started the production of this species, there are only four producing countries in 2020, with more than 90% of the production concentrated in the Iberian Peninsula. The objective of this paper is to analyse the economic performance of turbot companies in the EU between 2009 and 2020. In this way, biological, environmental, technological, political and social factors will be interrelated with the economic‐financial performance of the sector in order to reach a holistic understanding of this industry. The novelty of this paper lies in the fact that it is the first to analyse the profitability of the 22 turbot companies, aggregated by size and location, in the EU. The results show that the countries that have achieved success in the production of this species, and whose companies are still active today, are those in which several favourable circumstances converge. Among the most important factors are the location of the plants in the natural distribution area of turbot, an adequate institutional climate, and the financial and technological capacity of the companies. [ABSTRACT FROM AUTHOR]

In the Mediterranean and the Black Sea, aquaculture plays a major role in achieving food security and can deliver many socioeconomic benefits and reduce dependence on potentially overexploited wild stocks, provided it is managed properly. Given the importance of this sector and the growing demand for aquatic products, it is vital that aquaculture in the region be both sustainable and productive. In this regard, the General Fisheries Commission for the Mediterranean (GFCM) has identified, among the priorities of its GFCM 2030 Strategy for sustainable fisheries and aquaculture in the Mediterranean and the Black Sea, the need to promote practices supporting the sustainability of the sector and to maximize the sharing of technology and information in order to give producers the necessary tools and information on aquaculture production. This manual aims to support this endeavour by presenting detailed information about the rearing practices of Black Sea turbot (Scophthalmus maximus). It is divided into five parts. The first section provides an introduction into the status of the turbot aquaculture sector, as well as the necessary environmental conditions for optimal production. The second section describes the production of live food for turbot larvae beginning with microalgae, followed by rotifer and Artemia production. The third section details the management of broodstock, followed by the procedures for optimal larval and juvenile rearing in the fourth section. With a view to capitalizing on and promoting innovative technologies, the final section presents recent applications of biotechnologies to turbot production, namely, cryopreservation, triploidy and all-female stock production. [ABSTRACT FROM AUTHOR]

Non-synonymous variation (NSV) of protein coding genes represents raw material for selection to improve adaptation to the diverse environmental scenarios in wild and livestock populations. Many aquatic species face variations in temperature, salinity and biological factors throughout their distribution range that is reflected by the presence of allelic clines or local adaptation. The turbot (Scophthalmus maximus) is a flatfish of great commercial value with a flourishing aquaculture which has promoted the development of genomic resources. In this study, we developed the first atlas of NSVs in the turbot genome by resequencing 10 individuals from Northeast Atlantic Ocean. More than 50,000 NSVs where detected in the ~ 21,500 coding genes of the turbot genome, and we selected 18 NSVs to be genotyped using a single Mass ARRAY multiplex on 13 wild populations and three turbot farms. We detected signals of divergent selection on several genes related to growth, circadian rhythms, osmoregulation and oxygen binding in the different scenarios evaluated. Furthermore, we explored the impact of NSVs identified on the 3D structure and functional relationship of the correspondent proteins. In summary, our study provides a strategy to identify NSVs in species with consistently annotated and assembled genomes to ascertain their role in adaptation. [ABSTRACT FROM AUTHOR]

Live feed enrichments are often used in fish larvicultures as an optimized source of essential nutrients to improve larval growth and survival. In addition to this, they may also play an important role in structuring larval-associated microbial communities and may help improve their resistance to diseases. However, there is limited information available on how larval microbial communities and larviculture water are influenced by different live feed enrichments. In the present study, we investigated the effects of two commercial rotifer enrichments (ER) on turbot (Scophthalmus maximus) larval and post-larval gut-associated bacterial communities during larviculture production. We evaluated their effects on bacterial populations related to known pathogens and beneficial bacteria and their potential influence on the composition of bacterioplankton communities during larval rearing. High-throughput 16S rRNA gene sequencing was used to assess the effects of different rotifer enrichments (ER1 and ER2) on the structural diversity of bacterial communities of the whole turbot larvae 10 days after hatching (DAH), the post-larval gut 30 DAH, and the larviculture water. Our results showed that different rotifer feed enrichments were associated with significant differences in bacterial composition of turbot larvae 10 DAH, but not with the composition of larval gut communities 30 DAH or bacterioplankton communities 10 and 30 DAH. However, a more in-depth taxonomic analysis showed that there were significant differences in the abundance of Vibrionales in both 10 DAH larvae and in the 30 DAH post-larval gut fed different RE diets. Interestingly, the ER1 diet had a higher relative abundance of specific amplicon sequence variants (ASVs) related to potential Vibrio-antagonists belonging to the Roseobacter clade (e.g., Phaeobacter and Ruegeria at 10 DAH and Sulfitobacter at 30 DAH). In line with this, the diet was also associated with a lower relative abundance of Vibrio and a lower mortality. These results suggest that rotifer diets can affect colonization by Vibrio members in the guts of post-larval turbot. Overall, this study indicates that live feed enrichments can have modulatory effects on fish bacterial communities during the early stages of development, which includes the relative abundances of pathogenic and antagonist taxa in larviculture systems. [ABSTRACT FROM AUTHOR]

The experiment was to study the effect of different supplemental levels of Black soldier fly larvae powder on growth performance and serum biochemical indexes of turbot. A total of 240 juvenile turbot were randomly divided into four groups, with six replicates in each group and ten fish in each replicate. The fish in control group were fed with basic diet, and 15% group, 30% group and 45% group were fed with 15%, 30% and 45% Black soldier fly larvae powder instead of fish meal in basic diet, respectively. The pre-test lasted for 7 d and the formal test lasted for 60 d. The results showed that the final weight, WGR and CF of turbot in 45% group were significantly lower than those in control group and 15% group (P<0.05), and HSI in 30% group and 45% group was significantly lower than that in control group (P<0.05). Serum T-AOC and GSH-Px activity in 15% group and 30% group were significantly higher than those in control group (P<0.05). The activity of SOD in serum of turbot in experimental groups was significantly higher than that in control group (P<0.05). The activity of serum ACP in serum of turbot in 30% group and 45% group was significantly higher than that in control group (P<0.05), and the activity of ALP in serum of turbot in 45% group was significantly higher than that in control group (P<0.05). The serum TP content of turbot in 15% group and 30% group was significantly higher than that in control group, the serum ALT activity of turbot in 30% group was significantly higher than that in control group (P<0.05), and the serum TC content of turbot in experimental groups was significantly lower than that in control group (P<0.05). The experiment indicates that it is feasible to replace fish meal in diet with Black soldier fly larvae powder, and the effect of replacing 30% fish meal is better. [ABSTRACT FROM AUTHOR]