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The flathead gray mullet (Mugil cephalus L.) is a cosmopolitan fish that lives in warm and temperate zones over 42°N-42°S. It is a key fish species for industrial fishing off coastal Taiwan. Gray mullets enter the coastal waters of the southeastern Taiwan Strait (22°N-25°N) to spawn in winter and feed in the coastal and tidal waters of China (25°N-30°N). From 1986 to 2010, the annual catch of gray mullet decreased substantially and remained low. Although the Pacific Decadal Oscillation and El Niño-Southern Oscillation are recognized to affect gray mullet migration, the increase in sea surface temperature may be the main cause of the aforementioned decrease. We explored how weather changes affect fishing conditions and patterns at the gray mullet fishing grounds in Taiwan's coastal areas. Because of the decrease in gray mullet catches, the most common method for catching gray mullet in Taiwan's coastal areas between 1990 and 2010 was the use of drift or trawl nets instead of two-boat purse-seiner fleets. Since 2012, purse-seiner fleets have become the most common method for catching gray mullet. This trend indicates that the local fishing industry is adapting to changing environmental conditions.

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This research is devoted to assessing the pollution within a Mediterranean Sea area in the East coast of Algeria, which is known for its port and industrial activities. This study aims to assess the health status of the Gulf of Annaba located in the extreme North-East of Algeria by examining the contamination level by trace elements (Cu, Zn, Pb, Cd, Hg) in the sediments and muscles of Mugil cephalus fish. The obtained results manifest significant variations in metal levels in the sediments throughout the stations and the sampling seasons. The contamination by (Zn, Cu, Pb, Cd) of Joannonville and Sidi Salem stations is observed during both seasons whereas at the Chapuis station occurs only during the summer. The contamination indices are higher than 3, hence classifying the sediments of these three stations as "sediments at risk". Joannonville station manifests high levels of Hg only during the summer. For the muscles of M. cephalus, the contamination levels are found to be dependent on the species and the studied station. The fish inhabiting Joannonville and Sidi Salem show higher levels of (Zn, Pb, Cd) compared to the FAO/WHO standards, whereas the Pb level at Chapuis exceeds the standard during summer. Accordingly, the consumption of fish from Joannonville, Sidi Salem and Chapuis stations presents a serious threat regarding the toxicological risks based on the observed levels of contamination.

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Otolith features such as size and weight were analysed in 656 fish specimens of Chelon auratus, Chelon labrosus, Chelon saliens and Mugil cephalus collected from the Köycegiz Lagoon System, Aegean Sea, southwest Turkey. The aim was to calculate the asymmetry value of the otolith length (OL), otolith width (OW) and otolith weight (OWe). The asymmetry value of OL was greater than that of OW and OWe. The asymmetry value of the three otolith parameters increased with an increase in the fish's length. The probable cause of asymmetry in the otolith parameters investigated has been determined relative to the variability in growth prompted by ecological impact linked with the disparity in water temperature, salinity, depth and contaminants existing in the Köycegiz Lagoon System.

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Wild adult females of a low trophic omnivore teleost species, the flathead grey mullet (Mugil cephalus), caught in the western Mediterranean were sampled. The lipid and fatty acid composition of ovaries, liver, muscle, and peritoneal fat were analysed at previtellogenesis, early-vitellogenesis -first observed at mid-summer (early August)-, late-vitellogenesis, and the post-spawning period -from mid-September to mid-October-. During ovarian development, the lipid content of muscle was low and constant (3.85%-4.92%), indicating that the muscle was not used to store lipids for gonadal growth. Although constant, lipid content in the liver was higher (18.46%-22.62%) than in the muscle, and HSI% increased during gonad development, suggesting a dynamism in the mobilization of the hepatic lipids. Total lipids in the gonads significantly increased with maturation (from 4.90% to 34.59%) in parallel with the GSI (from 0.8% to 15.5%) to decrease after spawning. Peritoneal fat was probably transitional fat that could be rapidly metabolized or transferred to other tissues but no specific function could be assigned because its presence in previtellogenic and early-vitellogenic females varied greatly. One of the main sources of lipids accumulated in the ovary was most likely diet. The total percentage of ΣMUFA, mainly 17:1 -previously not identified in high quantities in teleost vitellogenic ovaries and likely of bacterial origin- and 16:1, strongly increased in the ovaries with maturation. The 16:1 might be an important source of lipids for embryo development. High percentages of DHA, EPA, and ARA were found in the ovary during previtellogenesis available to be used during gonadal maturation. Understanding lipid and fatty acid changes in broodstock tissues can increase our knowledge of the nutritional requirements of the fish used in aquaculture breeding programs.

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BACKGROUND: Determination of sex in fish without external sexual dimorphism is important. Sex determination of the flathead grey mullet (Mugil cephalus) in the culture system and spawn-producing and fish reproduction system is very important. Currently, there are several methods to determine the sex of fish; however, they are time-consuming, expensive and sometimes dangerous for the fish. OBJECTIVE: The purpose of this study was the sex determination of flathead grey mullet by ultrasonography as a safe and accurate method. METHODS: In this regard, 30 flathead grey mullets (early in their maturation) from a farm in Gomishan-Golestan province, Iran were examined using a portable ultrasound machine with a 6-12 MHz waterproof linear transducer. Scanning was performed on the ventral body surface in the sagittal and transverse planes, between ventral and anal fins. RESULTS: Differences in shape, qualitative size, echogenicity and the wall layers of the ovary and testis were evaluated for sex determination. Results of ultrasonography were confirmed immediately at necropsy. Ultrasonographic accuracy for sex determination was 100%. The speed of the procedure was around 30 s per fish. CONCLUSIONS: Overall, the sex determination of flathead grey mullet by ultrasonography was high in accuracy and speed, non-invasive and safe for fish and consumers, and may be considered a priority. Place of the organs in the M. cephalus coelomic cavity and the obtained experience showed that for rapid and easy sex identification, the best place to put the transducer is on the ventral surface of the fish in the caudal part of the coelomic cavity for taking transverse and sagittal ultrasonograms.

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Mugil cephalus Linnaeus, 1758 is a teleost fish widely distributed in coastal waters that plays an important role in commercial fisheries. In the present study, the complete mitogenome of M. cephalus from the Yellow Sea, China, was sequenced using Illumina Novaseq sequencing. The mitogenome of the M. cephalus was 16,744 bases in length (GenBank accession No. ON262567) including 2 rRNA genes, 22 tRNA genes, 13 protein-coding genes and a D-loop control region. The overall base composition of the genome was 28.2% A, 29.5% C, 26.9% T, and 15.4% G. The analysis of genetic similarity and phylogenetic relationship of M. cephalus from different geographic regions of the world indicated that the species from the Yellow Sea was most similar to NWP1 which is one of the three cryptic species of M. cephalus in Northwestern Pacific.

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Prosogonotrema iraqiense n. sp. (Sclerodistomidae: Prosogonotrematinae) is described in the flathead grey mullet, Mugil cephalus Linnaeus (Mugiliformes: Mugilidae), collected from the Arabian Gulf off Iraq during June and October 2019. Currently there are 11 species of ProsogonotremaVigueras, 1940 commonly accepted: Prosogonotrema arabicaYadav, 1980; Prosogonotrema bilabiatumVigueras, 1940 (type species); Prosogonotrema caesionisGu and Shen, 1979; Prosogonotrema diacanthiBilqees and Durrani, 1980; Prosogonotrema karachienseBilqees and Durrani, 1980; Prosogonotrema pavasiLokhande, 1990; Prosogonotrema piscicola (Srivastava, 1949) Gibson, 2002 (Syn. Bhaleraoia piscicolaSrivastava, 1949); Prosogonotrema plataxumGu and Shen, 1979; Prosogonotrema posterouterinaYadav, 1980; and Prosogonotrema symmetricumOshmarin, 1965 originally described from marine fishes, and Prosogonotrema nickoliBilqees and Khan, 1992 described from a freshwater cyprinid. Six additional species that have been considered synonyms of P. bilabiatum are also considered. Prosogonotrema diacanthi is considered a junior synonym of P. piscicola and Prosogonotrema carangiHussain and Rao, 1980nec Velasquez, 1961 is determined to be a species distinct from P. bilabiatum and is reassigned herein as Prosogonotrema aluteri nomen novum per the ICZN. Prosogonotrema iraqiense differs from all currently recognized species in the genus by having the width of the ventral sucker approach or exceed the width of the body and from all except P. pavasi (body length/width ratio 1:1.4-1:1.5) by having a distinctive narrower, more elongate body profile with a larger body length/width ratio (1:5.8-1:6.1 vs. 1: 2.0-1:4.1). A key to the 18 species we recognize in Prosogonotrema is included.

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Background: Treatment with recombinant gonadotropin hormones (rGths), follicle-stimulating hormone (rFsh) and luteinizing hormone (rLh), was shown to induce and complete vitellogenesis to finally obtain viable eggs and larvae in the flathead grey mullet (Mugil cephalus), a teleost arrested at early stages of gametogenesis in intensive captivity conditions. This study aimed to investigate the transcriptomic changes that occur in the ovary of females during the rGths-induced vitellogenesis. Methods: Ovarian samples were collected through biopsies from the same five females at four stages of ovarian development. RNASeq libraries were constructed for all stages studied, sequenced on an Illumina HiSeq4000, and a de novo transcriptome was constructed. Differentially expressed genes (DEGs) were identified between stages and the functional properties of DEGs were characterized by comparison with the gene ontology and Kyoto Encyclopedia. An enrichment analysis of molecular pathways was performed. Results: The de novo transcriptome comprised 287,089 transcripts after filtering. As vitellogenesis progressed, more genes were significantly upregulated than downregulated. The rFsh application induced ovarian development from previtellogenesis to early-to-mid-vitellogenesis with associated pathways enriched from upregulated DEGs related to ovarian steroidogenesis and reproductive development, cholesterol metabolism, ovarian growth and differentiation, lipid accumulation, and cell-to-cell adhesion pathways. The application of rFsh and rLh at early-to-mid-vitellogenesis induced the growth of oocytes to late-vitellogenesis and, with it, the enrichment of pathways from upregulated DEGs related to the production of energy, such as the lysosomes activity. The application of rLh at late-vitellogenesis induced the completion of vitellogenesis with the enrichment of pathways linked with the switch from vitellogenesis to oocyte maturation. Conclusion: The DEGs and enriched molecular pathways described during the induced vitellogenesis of flathead grey mullet with rGths were typical of natural oogenesis reported for other fish species. Present results add new knowledge to the rGths action to further raise the possibility of using rGths in species that present similar reproductive disorders in aquaculture, the aquarium industry as well as the conservation of endangered species.

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Mugil cephalus L., 1758 (flathead mullet) is a valuable commercial fish and a promising object of artificial breeding in the Black Sea and the Sea of Azov, and the study of its parasite fauna is important for fishery and mariculture. Monogeneans of the genus Ligophorus are common ectoparasites dwelling on the gills of mullets. Two representatives of this genus parasitise flathead mullet in the Azov-Black Sea region, namely Ligophorus mediterraneus Sarabeev, Balbuena et Euzet, 2005 and Ligophorus cephali Rubtsova, Balbuena, Sarabeev, Blasco- Costa et Euzet, 2006. Morphological identification of these species requires spending much time and a high level of experience in monogenean taxonomy. For quick and correct species identification of these parasites, we have developed a genotyping approach based on the polymerase chain reaction of allele-specific gene sites for various Monogenea species. A fragment of the 28S ribosomal gene, which includes conserved and variable sites, was chosen as a genetic marker. Three approaches were used as follows: amplified fragment length analysis, allelespecific PCR with endpoint detection and allele-specific real-time PCR using SYBR Green intercalating dye. The first approach was by obtaining PCR products of different lengths that were specific either to L. mediterraneus or to L. cephali. This approach was implemented due to the presence of several variable sites located at a distance from each other. The PCR mixture contained three primers: one forward and two reverse. The forward primer was complementary to the conserved site, which did not differ between species. Reverse primers were speciesspecific and, for each species, they were complementary to different DNA regions located 100 bp apart. As a result, L. mediterraneus was characterized by shorter amplicons than L. cephali. For the second and third approaches, a pair of primers was designed according to the following principle: the forward primer was complementary to both species, since it was selected for the conserved gene region. Reverse primers were species-specific and were designed for the 28S variable region. The two parasite species were distinguished by three-point mutations. Thus, one pair of primers was complementary to L. mediterraneus, the other, to L. cephali. The amplified fragment length analysis and the allele-specific real-time PCR demonstrated 100 % coincidence of genotyping results compared with Sanger sequencing. The developed genotyping protocols can be used not only to distinguish two species of Ligophorus from flathead mullet in ecological studies and veterinary practice but also for further development of similar approaches for other monogeneans, among which there are many pathogenic species.

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Background and Aim: Antibiotic resistance has been a progressively documented problem, resulting in treatment failure in humans and animals. This study aimed to investigate the antimicrobial susceptibility and virulence of extensively drug-resistant (XDR) Aeromonas spp. in wild Mugil cephalus and its surrounding seawater along the coastal road of Port Said, Egypt. Materials and Methods: Specimens were examined bacteriologically, confirmed biochemically, and tested for their sensitivity against 11 antimicrobial agents. Molecular confirmation of the obtained isolates by 16S rRNA was performed, followed by the detection of antimicrobial resistance and virulence genes. Results: Aeromonas spp. was recovered from fish (44%) and water samples (36%). A. hydrophila was the most prevalent identified strain, followed by Aeromonas sobria, Aeromonas caviae, and Aeromonas schubertii. Moreover, 90% of the tested isolates were multidrug-resistant (MDR), while 26.67% were XDR. Tested isolates were resistant to b-lactams and sulfonamides (100%), oxytetracycline (90%), and streptomycin (62.22%) but completely susceptible to cefotaxime. XDR isolates successfully amplified resistance genes (blaTEM , sul1, and tetA(A)) but not the (aadA1) gene, although there was phenotypic resistance to streptomycin on plates. All XDR isolates carry the cytotoxic enterotoxin gene (act), but alt gene was detected in only one isolate (12.5%). Conclusion: Data in this study provide a recent update and highlight the role of wild mullet and seawater as reservoirs for MDR and XDR Aeromonas spp. that may pose a risk to humans as food-borne infection or following direct contact.

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Microplastic pollution is an extremely emerging problem and its potential threats to the aquatic organisms were investigated worldwide. In this study, four different commercial fish species (Mullus barbatus (Linnaeus, 1758), Mullus surmuletus (Linnaeus, 1758), Mugil cephalus (Linnaeus, 1758), Saurida undosquamis (Richardson, 1848)) were used as a bioindicator to assess the microplastic pollution in the northeastern Mediterranean. The frequency of occurrence in the gastrointestinal tract (GIT) and gill was varied between 66-100% and 68-90%, respectively. The highest microplastic abundance was detected at the GIT of M. cephalus sampled from Asi River estuary. The majority of extracted microplastics were fiber, black in color and less than 1 mm in size. Fourier Transform Infrared Spectroscopy (FTIR) indicated the most common polymer type as polyethylene. This study is the first study examining the microplastic existence in gill and results obtained in this study improve the knowledge about the relationship of microplastic ingestion in fish and environmental conditions in the Northeastern Mediterranean Sea.

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The COVID-19 global pandemic-related restrictions during 2020 severely impacted the Australian seafood industry, including essential scientific monitoring to support stock assessment and to demonstrate sustainability. Here we detail a novel, collaborative monitoring program between scientists and the seafood industry to generate length and age compositions that were representative of one of the largest, most valuable, and controversial fisheries along eastern Australia, the pre-spawning ocean run fishery for Sea Mullet Mugil cephalus that is predominantly a roe fishery. The standard approach to monitoring this fishery has been to base trained scientific staff at the major processing facility for M. cephalus, where they access whole fish from entire catches to generate representative length and age compositions during the peak season, April to May. Covid-19 restrictions prevented this approach for 2020 in eastern Australia. In recognition that in addition to the high-value roe, all components of the female fish are utilized (heads and guts for bait, bodies for human consumption), a multi-stage, spatially stratified sampling design was investigated. Female heads were retained from randomly selected catches from each of the three major fishing zones and transported to the New South Wales Department of Primary Industries fish laboratory based in Sydney. Head lengths (HLs) were measured and converted to Fork Lengths (FLs) using a HL to FL relationship. The resulting fish length compositions from each catch were subsequently combined based on: (i) relative catch size of females within an ocean zone, and; (ii) the relative reported landings of females in each ocean fishing zone. Otoliths were randomly collected from heads sampled from each ocean zone and used to estimate age. The resulting ocean zone to age matrix was combined with the relative reported landings of female fish in each ocean fishing zone to generate a total female age composition for the fishery. The estimated age composition of females were typical in being mainly between ages 3 and 6, with a strong presence of 4-year olds. This stronger cohort was present as 3-year olds in 2018/19 and 5-year olds in 2020/21, thus providing confidence that our sampling was representative of the fishery. The study reinforces the positive outcomes that can be generated through co-management between scientists and the seafood industry.

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The assessment of the environmental quality of a sensitive karst aquatic system under the centuries-long anthropogenic influence of the coal mining industry is important for both improving the quality of water resources and protecting aquatic wildlife and human health. In this study, we investigated the anthropogenic impact on the aquatic environment of the upper and middle course of the Rasa River through the analysis of a suite of metal(loid)s in three aquatic compartments (water, sediment, fish) using inductively coupled plasma mass spectrometry (ICP-MS). Concentrations of inorganic constituents in water were low, while the chemical composition of stream sediments mainly reflected the geological background of the area, indicating the origin of metal(loid)s from predominantly natural sources. Although comparison with PEC-Q values indicated that existing sediment quality conditions could pose a threat to benthic organisms with regard to Cr and Ni, the constant vertical profiles of these elements suggested their natural origin from the weathering of flysch. Element levels in the muscle of targeted fish species were in accordance with the values typical for low-contaminated freshwater systems, while levels of Cd, Pb and Hg were mostly below the European regulatory limits for toxic elements in foods, indicating that the low concentrations of most contaminants in muscles of fish from the Rasa River do not present a risk to humans or other consumers. The obtained data indicated a generally low contamination status of the western part of the Rasa River basin with regard to the analyzed inorganic elements.

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The aim of this study was to evaluate the presence of plastic debris in the stomach contents of two commercially important species Ethmidium maculatum and Mugil cephalus from Peru and relate their characteristics to their diet. The contents of 1820 stomachs were analyzed visually to detect the presence of plastics and prey. Of the analyzed samples, 0.3% contained nine microplastic fragments (0.72-4.54 mm) and one mesoplastic fragment (6.65 mm). Green and blue plastics of polyethylene and polypropylene were the most common. In E. maculatum, copepods were the main prey, followed by diatoms and decapods, and they exhibited the highest amount of plastics. In M. cephalus, the main prey were diatoms, copepods, and dinoflagellates, and they exhibited only one type of microplastic. Although the characteristics of the plastics and the prey of these species may be related (sizes-colors), more research is required to understand this problem in commercially important fishery resources in Peru.

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Adult trematodes, morphologically similar to Haplosplanchnus pachysomus (Eysenhardt, 1829), were extracted from the intestine of Mugil cephalus Linnaeus, 1758, collected in the Black Sea basin. Morphological, morphometric and 28S ribosomal DNA (rDNA) partial sequence data were obtained for these trematodes following comparative analysis with previous data on this species. Worms from this study were morphologically identical to all previously reported H. pachysomus specimens from different locations. The results of the morphometric analysis indicated general similarity between H. pachysomus from the Black Sea and trematodes from Vietnam and Australia. Trematodes from the Black Sea and specimens from Spain were identical based on 28S rDNA partial sequences; however, these sequences differed from that of H. pachysomus from Vietnam and Australia by eight fixed substitutions. Overall, our results indicate that H. pachysomus from Spain and the Black Sea and from Vietnam and Australia can presently be considered as two cryptic species, one in Palaearctic and one in Indo-West Pacific regions. Our results provide a molecular base for including Haplosplanchnus purii in the genus Provitellotrema or to consider H. purii, P. crenimugilis and H. pachysomus within the same genus.

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Lactococcus garvieae (L. garvieae) is an important pathogen that causes enormous economic losses in both marine and freshwater aquaculture. At present, antibiotics are the only option for farmers to reduce the losses caused by L. garvieae. However, the usage of antibiotics leads to environmental pollution and the production of drug-resistant strains of bacteria. Therefore, vaccination is preferred as an alternative method to prevent infectious diseases. In this study, we describe an effective approach to the production of an oral biofilm vaccine, using bacteria grown on chitosan particles to form biofilms, and thus providing an inactive pathogen that enhances the immune response in fish. We observed the formation of a biofilm on chitosan particles and administered the novel oral biofilm vaccine to fish. We analyzed the immune responses, including antibody production, phagocytic ability, albumin/globulin ratio and immune-related genes, of vaccinated and control groups of black mullet. Our results show that the phagocytic ability of the biofilm vaccine group was 84%, which is significantly higher than that of the control group, and the antibody production in this group was significantly higher compared with the other group. The mRNA expression levels of immune-related genes (TLR2, IL-1ß, TNF-α) were significantly upregulated in the spleen after vaccination. In challenge experiments, the relative percent survival (RPS) was 77% in the biofilm vaccine group, 18% in the whole-cell vaccine group, and 0% in the chitosan particle group at 32 days post-vaccination. In addition, we also found that the relative percent survival (RPS) at 1 day post-vaccination was 74% in the biofilm vaccine group, 42% in the whole-cell vaccine group, and 26% in the chitosan particle group. In both long-term and short-term challenge experiments, the viability of the biofilm vaccine group was significantly higher than that of the whole-cell, chitosan particle and PBS groups. We conclude that based on its protective effect, the L. garvieae biofilm vaccine is better than the whole-cell vaccine when challenged several weeks after vaccination. In addition, the biofilm vaccine also has a greater protective effect than the whole-cell vaccine when challenged immediately after vaccination. Therefore, the biofilm vaccine might represent a novel method for the prevention and treatment of L. garvieae infection.

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BACKGROUND: Fish farming is one of the most productive economies in the world. One of the essential goals in fish production is to minimize processing costs while maintaining and increasing the vital functions, weight and immunity of fish. OBJECTIVE: We conducted this study to explore nanoselenium (Nano-Se) particles in various feeding schemes. MATERIAL AND METHOD: Nano-Se particles incorporated in the basal diet at (0.5 mg/kg diet), and the fish was divided into six groups after adaptation as the follows: The first group was feed daily with a diet containing Nano-Se (0.5 mg/kg diet); the second group was exposed to a feeding programme in which it has day feeding followed by day of starvation with a diet containing Nano-Se (0.5 mg/kg diet); the third group was day feeding followed by 2 days of starvation; the fourth group served as a negative control group in which this group was continuous feeding with a basal diet without Nano-Se; the fifth group was day feeding with the basal diet followed by a day of starvation; and the sixth group was day feeding with basal diet followed by 2 days of starvation. RESULT: Our result revealed that Group 2 showed significant improvement in haematological parameters, red blood cells and haemoglobin with a substantial increase in total protein (p < 0.05) as well as lysosomal and phagocytic activity with considerable upregulation of growth hormone and insulin growth factor 1 in addition to markedly increase in the pro-inflammatory cytokines. Finally, this study offers the first-time dietary regime with Nano-Se supplementation that saves the feeding cost and increases fish welfare and growth.

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Lactococcosis [Lactococcus garvieae (LG)] is one of the most prevalent bacterial diseases affecting grey mullet (Mugil cephalus) aquaculture. Therefore, the present research evaluated the efficacy of formalin-killed LG vaccine with an oil-based adjuvant in grey mullet under laboratory and field trials. The laboratory evaluation for LG vaccine and its cross-protection upon challenge in grey mullet found that single-dose immunization of formalin-killed LG with adjuvant resulted in 91.4% and 100% relative per cent survival (RPS) when challenged with homologous and heterologous strains. The levels of specific antibody titre and lysozyme activity increased significantly in the vaccinated group. Immune gene expression at 24 hr after challenge showed an increase in levels of pro-inflammatory and anti-inflammatory cytokines. A parallel field trial experiment was conducted to investigate the long-term effectiveness of the LG vaccine. Results demonstrated that at one month and three months post-immunization with heterologous strain, 100% RPS was recorded in the vaccinated group. The findings suggested that the formalin-inactivated LG vaccine strain (S3) protected grey mullet against LG infection for a period of three months.

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Flathead gray mullet (Mugil cephalus) is a cosmopolitan mugilid species popular in fishery and aquaculture with an economic preference for all-female population. However, it displays neither sexual dimorphisms nor heteromorphic sex chromosomes. We have previously presented a microsatellite-based linkage map for this species locating a single sex determination region (SDR) on linkage group 9 (LG9) with evidence for XX/XY sex determination (SD) mechanism. In this work, we refine the critical SDR on LG9, and propose positional- and functional- candidate genes for SD. To elucidate the genetic mechanism of SD, we assembled and compared male and female genomic sequences of 19 syntenic genes within the putative SDR on mullet's LG9, based on orthology to tilapia's LG8 (tLG8) physical map. A total of 25 sequence-based markers in 12 genes were developed. For all markers, we observed association with sex in at least one of the two analyzed M. cephalus full-sib families, but not in the wild-type population. Recombination events were inferred within families thus setting the SDR boundaries to a region orthologous to ∼0.9 Mbp with 27 genes on tLG8. As the sexual phenotype is evident only in adults, larvae were assigned into two putative sex-groups according to their paternal haplotypes, following a model of XY/XX SD-system. A total of 107 sex-biased differentially expressed genes in larvae were observed, of which 51 were mapped to tLG8 (48% enrichment), as compared to 5% in random control. Furthermore, 23 of the 107 genes displayed sex-specific expression; and 22 of these genes were positioned to tLG8, indicating 96% enrichment. Of the 27 SDR genes, BCCIP, DHX32A, DOCK1, and FSHR (GTH-RI) are suggested as positional and functional gene candidates for SD.

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The environmental monitoring of chemical toxicants has been a widely studied topic in the last few decades. The main aim of the present study was to determine the total concentration of nine elements (Cd, Cr, Pb, Ni, Al, Cu, Fe, Mn, and Zn) in the fish species grey mullet (M. cephalus) and in the coastal marine waters collected from various sampling points along the Black Sea (Bulgaria) and the Ionian Sea (Italy). Further, those results were applied to predict the pollution degree in those coastal marine environments. The fish samples were subject to acid digestion followed by appropriate analytical determination. The metal concentrations in marine water samples collected from the Black Sea (Bulgaria) and the Ionian Sea (Italy) were also analyzed. Unpaired Student's t-test and the one-way ANOVA were applied for the statistical analysis of the data. The statistical results revealed a significant variation (p < 0.0001) in the concentration of various fish tissues. The accumulation of toxic and essential elements differs significantly in grey mullet species caught from the Black Sea (Bulgaria) and the Ionian Sea (Italy). The results from this study may serve as a convenient approach during marine pollution programs set by both countries (Italy and Bulgaria).