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Obtaining robust estimates of population abundance is a central challenge hindering the conservation and management of many threatened and exploited species. Close-kin mark-recapture (CKMR) is a genetics-based approach that has strong potential to improve the monitoring of data-limited species by enabling estimates of abundance, survival, and other parameters for populations that are challenging to assess. However, CKMR models have received limited sensitivity testing under realistic population dynamics and sampling scenarios, impeding the application of the method in population monitoring programs and stock assessments. Here, we use individual-based simulation to examine how unmodeled population dynamics and aging uncertainty affect the accuracy and precision of CKMR parameter estimates under different sampling strategies. We then present adapted models that correct the biases that arise from model misspecification. Our results demonstrate that a simple base-case CKMR model produces robust estimates of population abundance with stable populations that breed annually; however, if a population trend or non-annual breeding dynamics are present, or if year-specific estimates of abundance are desired, a more complex CKMR model must be constructed. In addition, we show that CKMR can generate reliable abundance estimates for adults from a variety of sampling strategies, including juvenile-focused sampling where adults are never directly observed (and aging error is minimal). Finally, we apply a CKMR model that has been adapted for population growth and intermittent breeding to two decades of genetic data from juvenile lemon sharks (Negaprion brevirostris) in Bimini, Bahamas, to demonstrate how application of CKMR to samples drawn solely from juveniles can contribute to monitoring efforts for highly mobile populations. Overall, this study expands our understanding of the biological factors and sampling decisions that cause bias in CKMR models, identifies key areas for future inquiry, and provides recommendations that can aid biologists in planning and implementing an effective CKMR study, particularly for long-lived data-limited species.

To enhance the accuracy of fine-grained classification of shark populations and address issues such as image interference, insufficient extraction of local key features, and lack of semantic correlation between channels, a DM-BCNN model for fine-grained classification of shark populations based on an improved Bilinear Convolutional Neural Network (B-CNN) is proposed. First, deformable convolution is introduced to replace the feature extraction part of the original model with a DRAM_ResNet network structure, enhancing the model's ability to detect complex and irregular shapes and local structures. Then, the NAM attention mechanism is employed to strengthen the model's ability to identify and extract key features. Finally, a Mutual Channel Loss function is introduced to enhance the semantic correlation between different channels of shark images, allowing the model to capture information from various aspects of the images more comprehensively. The results show that the improved DM-BCNN model achieved a Top-1 accuracy of 96. 12%, representing a 2.51 percentage point improvement over the original model. The study demonstrates that the proposed improved model outperforms the original model in fine-grained image classification, making it more effective for fine-grained classification and identification of shark populations. [ABSTRACT FROM AUTHOR]

Depredation (the partial or complete removal of a hooked species by a non‐target species) is a human–wildlife conflict as old as humans and the sea. In some ways, depredation is no different today than it was a century ago. But in many ways, this conflict has become more complicated. Following three decades of successful management, some US shark populations have begun to rebuild. However, many anglers attribute perceived increases in shark depredation to management measures, claiming they have led to 'overpopulation' of sharks and/or learned behaviour by sharks. We investigated whether these factors could explain the reported increases in depredation. Based on fishery‐independent surveys, neither shark population increases nor learned behaviour by sharks is evident. However, increases in angler effort provide an alternative explanation that is not often considered. While far from a smoking gun, at least four themes emerge from this thought exercise. First, it is important to understand historical predator baselines. Second, it is important to acknowledge lifting baselines, that is, instances where previously depleted populations are recovering. Third, it is important to remember that there are many instances when stakeholder observations were initially misaligned with traditional scientific observations but were ultimately recognized as pivotal for filling data gaps. Finally, and perhaps most important, is the acknowledgement that perceived conflict is as potent as real conflict. Arguably, it may not matter if depredation has increased or decreased; the overwhelming perception from stakeholders is an increase in depredation, and this is the perceived (or real) conflict that must be addressed. [ABSTRACT FROM AUTHOR]

The linear axial expansion transport method avoids the negative source problem caused by transverse leakage in the traditional two-dimensional/one-dimensional (2D/1D) transport method and has better stability. However, stability is poor with the coarse-mesh finite difference (CMFD) accelerated linear axial expansion transport method. In this paper, the stability of the partial current–based coarse-mesh finite difference (p-CMFD) method, the optimally diffusive coarse-mesh finite difference (od-CMFD) method, and the linear prolongation coarse-mesh finite difference (lp-CMFD) method is studied based on Fourier analysis. The results of the Fourier analysis indicate that the problem is stable for axial coarse-mesh optical thickness less than 2 or larger than 50; the calculation diverges when the axial coarse-mesh optical thickness is between 2 and 50. The numerical results of the KUCA benchmark problem are the same as the results of the Fourier analysis. [ABSTRACT FROM AUTHOR]

Objective: The Blackchin Guitarfish Glaucostegus cemiculus is endemic to the Mediterranean Sea and is critically endangered, but relevant routine laboratory data are unavailable. Our objectives were to determine the packed cell volume (PCV), comprehensive serum chemistry analytes, and serum total thyroxine (sTT4) concentration; compare serum albumin and serum globulin concentrations as measured by two different methods; and describe the blood cell morphology of healthy, free‐ranging Blackchin Guitarfish. Methods: Wild Blackchin Guitarfish were captured using a seine net. Blood samples for serum chemistry and hematological analyses were obtained and measured using routine laboratory methods. The fish were tagged and released. Result: This study included 43 Blackchin Guitarfish (17 males and 26 females) that were younger than 6 months as estimated based on total length and body weight. The median PCV (n = 23) was 22% (minimum–maximum [min–max] = 15–25%). Median sTT4 (n = 10) measured by chemiluminescence immunoassay was 7.86 nmol/L (min–max = 7.52–9.57 nmol/L). The study included a comprehensive, 25‐analyte serum chemistry analysis (e.g., serum iron and unbound and total iron‐binding capacity) and a morphological description of all blood cells. Serum electrophoresis (SEP; n = 13) yielded a consistent serum albumin‐migrating protein fraction and four globulin fractions. Serum electrophoretograms corroborating these results are presented. Conclusion: In Blackchin Guitarfish, the serum albumin‐migrating fraction measured by SEP combined with serum total protein concentration yields a much higher albumin concentration compared to that measured by bromocresol green spectrophotometry. The true identity of this albumin‐migrating fraction remains to be identified. The analytes' calculated 2.5–97.5% interpercentile intervals should be considered as reference intervals applying to Blackchin Guitarfish of similar age but should be applied cautiously to adult fish. Impact statementThis study incudes novel comprehensive basic laboratory data describing young, healthy Blackchin Guitarfish, a critically endangered species in the Mediterranean Sea. The findings significantly increase the scientific knowledge of this species, potentially contributing to its conservation. [ABSTRACT FROM AUTHOR]

Plastic pollution represents a global environmental issue. Awareness of plastic pollution in marine organisms increased strongly during the last decades, including chondrichthyans. Due to a lack of a broad and comprehensive view of this global issue in chondrichthyans, we synthesized the 48 publications covering 54 species since 2002, and employed bibliometric analysis and data exploration to summarize the historical progression of the development, characteristics of plastics in chondrichthyans and evaluate their potential impacts across various regions, habitats, and Red List categories. The bibliometric analysis revealed that the investigation of plastic distribution in demersal sharks inhabiting the nearshore areas of the Mediterranean and northeastern Atlantic Ocean is a major research focus. Based on the current evaluation, plastics have been ubiquitously discovered within sharks, skates, and rays; however, only less than 5% of chondrichthyans worldwide have been investigated. Among these, 25 species are classified under one of the three threatened categories (critically endangered, endangered or vulnerable), according to IUCN Red List. The average abundance (all specimens) and load (specimens that contained plastics) in chondrichthyans were 2.86 ± 7.71 items/individual and 4.91 ± 9.39 items/individual, respectively. Plastic abundance/load is not influenced by the sampling regions, habitats, or Red List categories; however, higher records were found in the endangered and near threatened species. The plastics are predominantly fibrous in shape, with blue and black being the predominant colors, along with polypropylene and polyethylene in polymer type. Notably, inconsistencies in sampling, processing, and identification methods across studies might impeded the integration and comparison of data. This review highlights the potential implications of plastic pollution from chondrichthyans on biodiversity conservation and emphasizes the necessity to consider intra- and inter-specific variations in biometric and ecological characteristics, as well as establish standardized protocols to facilitate effective comparisons in contamination dynamics between studies of chondrichthyans. [ABSTRACT FROM AUTHOR]

Trypsin is a protease that breaks protein peptide bonds. Fish intestines can be used as an alternative raw material for trypsin. Trypsin enzymes from the intestines of different fish species have different characteristics. This study aimed to determine the characteristics and stability of trypsin enzyme in NaCl extracted from fish intestines based on differences in fish species. Trypsin activity was optimal at 50 °C and pH 8, with specific activity values of 0.5993 U/mg in rabbitfish, 0.3880 U/mg in sharks, and 0.6964 U/mg in flatfish. The maximum reaction speed (Vmax) was the highest for trypsin from the intestine of rabbitfish (0.2585 mmol/s), followed by flatfish (0.1042 mmol/s), and shark (0.0599 mmol/s). The lowest Km value was obtained for trypsin from sharks (0.4084 mM), followed by flatfish (1.0253 mM), and rabbitfish (4.5952 mM). Trypsin from the intestines of rabbitfish and flatfish was stable in NaCl solution (concentration 5-30%), as it can maintain a relative activity of more than 50%. In contrast, trypsin extracted from the intestines of milk fish had a relative activity below 21%. The average molecular weights of the three trypsin enzymes were 26.8, 27.2; and 21.9 kDa, respectively. Differences in the type of fish affected trypsin enzyme activity. Flatfish are omnivorous, and rabbitfish, as herbivores, have better enzyme activity values than sharks, as carnivores.

Because the elastic scattering cross sections of medium-mass nuclides have very strong elastic scattering resonance phenomenon in the fast neutron region, which will lead to the self-shielding effect of energy scale and make distortions of the neutron flux distribution to zigzagging. In order to accurately describe the distribution of neutron flux in the energy scale, the deterministic one-step method needs to divide a large number of energy intervals for description, and the number of energy groups is generally thousands. Deterministic one-step transport calculation has large memory and low computational efficiency with thousands of groups. In the traditional calculation of the whole-core non-uniform transport calculation for the thousands of groups, the section generation software was mainly used to prepare the self-shielding cross section by using the ultra-fine groups, and then the broad-group cross section was prepared offline by the transport calculation of the equivalent model of cells or components. Finally, the deterministic one-step program was used to calculate the whole-core non-uniform transport. The broad-group cross sections prepared off-line cannot reflect the characteristics of materials of different reactor locations and bring the approximations. In order to solve the problem that the thousand-group energy structure of fast reactors leads to the high computational cost of the deterministic one-step method, an online energy group condensation method with fine group energy spectrum based on SHARK was developed. For the fuel cells of fast reactors, it can keep the composition of fuel and other materials unchanged and search the radius of the fuel to make the escape cross section conserved. It has the capability of online equivalent model establishment, online calculation of fine group energy spectrum and broad group cross sections condensation. For non-fuel cells, the broad group cross section was condensed using the fine group energy spectrum calculated by the one-dimensionalal constant volume model of practical problems. Based on the MOX1000 material of the benchmark for neutronic analysis of sodium-cooled fast reactor cores, a two-dimensional 5×5 rectangular single-assembly problem and a two-dimensional 3×3 multi-assembly problem were constructed and calculated. The numerical results show that compared with the calculation results of the group in 1 968, the acceleration ratio of the online energy group condensation method in the two-dimensional 5×5 rectangular single-assembly problem is 8 to 18 and that in the two-dimensional 3×3 multi-assembly problem is 12 to 17, which can significantly improve the calculation efficiency. In terms of calculation accuracy, the relative deviation of pin power distribution is less than 1%, and the maximum deviation of eigenvalue is about 360 pcm. It is of great significance to deterministic one-step method for fast reactor transport calculation.

Purse‐seine tropical tuna fishing in the eastern tropical Pacific Ocean (EPO) results in the bycatch of several sensitive species groups, including elasmobranchs. Effective ecosystem management balances conservation and resource use and requires considering trade‐offs and synergies. Seasonal and adaptive spatial measures can reduce fisheries impacts on nontarget species while maintaining or increasing target catches. Identifying persistently high‐risk areas in the open ocean, where dynamic environmental conditions drive changes in species' distributions, is essential for exploring the impact of fisheries closures. We used fisheries observer data collected from 1995 to 2021 to explore the spatiotemporal persistence of areas of high bycatch risk for 2 species of oceanic sharks, silky shark (Carcharhinus falciformis) and oceanic whitetip shark (Carcharhinus longimanus), and of low tuna catch rates. We analyzed data collected by fisheries scientific observers onboard approximately 200 large purse‐seine vessels operating in the EPO under 10 different flags. Fishing effort, catch, and bycatch data were aggregated spatially and temporally at 1° × 1° cells and monthly, respectively. When areas of high fishing inefficiency were closed the entire study period and effort was reallocated proportionally to reflect historical effort patterns, yearly tuna catch appeared to increase by 1–11%, whereas bycatch of silky and oceanic whitetip sharks decreased by 10–19% and 9%, respectively. Prior to fishing effort redistribution, bycatch reductions accrued to 21–41% and 14% for silky and oceanic whitetip sharks, respectively. Our results are consistent with previous findings and demonstrate the high potential for reducing elasmobranch bycatch in the EPO without compromising catch rates of target tuna species. They also highlight the need to consider new dynamic and adaptive management measures to more efficiently fulfill conservation and sustainability objectives for exploited resources in the EPO. [ABSTRACT FROM AUTHOR]

Climate change is an environmental emergency threatening species and ecosystems globally. Oceans have absorbed about 90% of anthropogenic heat and 20%–30% of the carbon emissions, resulting in ocean warming, acidification, deoxygenation, changes in ocean stratification and nutrient availability, and more severe extreme events. Given predictions of further changes, there is a critical need to understand how marine species will be affected. Here, we used an integrated risk assessment framework to evaluate the vulnerability of 132 chondrichthyans in the Eastern Tropical Pacific (ETP) to the impacts of climate change. Taking a precautionary view, we found that almost a quarter (23%) of the ETP chondrichthyan species evaluated were highly vulnerable to climate change, and much of the rest (76%) were moderately vulnerable. Most of the highly vulnerable species are batoids (77%), and a large proportion (90%) are coastal or pelagic species that use coastal habitats as nurseries. Six species of batoids were highly vulnerable in all three components of the assessment (exposure, sensitivity and adaptive capacity). This assessment indicates that coastal species, particularly those relying on inshore nursery areas are the most vulnerable to climate change. Ocean warming, in combination with acidification and potential deoxygenation, will likely have widespread effects on ETP chondrichthyan species, but coastal species may also contend with changes in freshwater inputs, salinity, and sea level rise. This climate‐related vulnerability is compounded by other anthropogenic factors, such as overfishing and habitat degradation already occurring in the region. Mitigating the impacts of climate change on ETP chondrichthyans involves a range of approaches that include addressing habitat degradation, sustainability of exploitation, and species‐specific actions may be required for species at higher risk. The assessment also highlighted the need to further understand climate change's impacts on key ETP habitats and processes and identified knowledge gaps on ETP chondrichthyan species. [ABSTRACT FROM AUTHOR]

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Introduction: Fungal diseases are frequently associated with elevated mortality rates in elasmobranchs. Currently, there is a notable absence of scientifically validated therapeutic medications that can ensure both effectiveness and safety when administered to this group of animals. The empirical prescription of azole antifungal agents, particularly voriconazole, has been posited as a potentially efficacious treatment approach for addressing most common mycoses in sharks and rays. However, there are still no published pharmacokinetic studies supporting its use in elasmobranchs and there is a lack of scientific base for its utilization in elasmobranchs. Methods: For this study, voriconazole was administered intravenously (IV) and intramuscularly (IM), at a single dose of 4 mg/kg to six adult undulate skates (Raja undulata). A washout period of 8 weeks was left between each route of administration. Blood samples were collected both before and at ten predetermined intervals after each dosing (0.25, 0.5, 1, 1.5, 2, 4, 8, 12, 24, and 36 h after drug administration). Plasma concentrations were quantified using a validated high-performance liquid chromatography method, and pharmacokinetic (PK) data was analyzed through non-compartmental methods. Results: The mean extrapolated concentration at 0 h (C0) after IV administration was 27.19 ± 7.15 µg/mL and the mean peak plasma concentrations (Cmax) ± SEM after IM administration resulted 2.98 ± 0.28 µg/mL at a mean time to maximum concentration (T max) of 1.33 ± 0.17 h. Terminal half-lives were calculated and resulted 11.18 ± 1.32 h for IV injections and 9.59 ± 1.38 h for IM injections. The area under the curve extrapolated to infinity was determined as 58.14 ± 2.79 h·µg/ml following IV injections and 37.60 ± 6.67 h·µg/ml following IM injections. The IM-administered voriconazole exhibited a mean absolute bioavailability of 64.67 ± 11.47%. Discussion: These discoveries provide backing for the possible application of voriconazole through the intramuscular route in undulate skates and support using lower dosage regimens compared to those required for oral administration, emphasizing the importance of conducting further pharmacokinetic studies with antifungals in elasmobranchs. [ABSTRACT FROM AUTHOR]

Glucose has important roles in the development of zebrafish, the vertebrate animal model; however, in most oviparous animals, the amount of maternally provided glucose in the yolk is scarce. For these reasons, developing animals need some ways to supplement glucose. Recently, it was found that developing zebrafish, a teleost fish, undergo gluconeogenesis in the yolk syncytial layer (YSL), an extraembryonic tissue that surrounds the yolk. However, teleost YSL is evolutionarily unique, and it is not clear how other vertebrates supplement glucose. In this study, we used cloudy catshark (or Torazame catshark), an elasmobranch species which possesses a YSL‐like tissue during development, and sought for possible gluconeogenic activities in this tissue. In their yolk sac, glucose increased, and our isotope tracking analysis detected gluconeogenic activities with glycerol most preferred substrate. In addition, many of gluconeogenic genes were expressed at the YSL‐like tissue, suggesting that cloudy catshark engages in gluconeogenesis in this tissue. The gluconeogenesis in teleost YSL and a similar tissue in elasmobranch species implies conserved mechanisms of yolk metabolism between these two lineages. Future studies on other vertebrate taxa will be helpful to understand the evolutionary changes in the modes of yolk metabolism that vertebrates have experienced. [ABSTRACT FROM AUTHOR]

The Indo-Australian Archipelago (IAA) today exhibits the highest marine biodiversity, which has been evolving since the early Miocene. The existence of this high palaeobiodiversity is attested to by the presence of many fossil invertebrates; however, the region's fossil fish record is sparse and understudied, which is also the case for cartilaginous fishes. Elasmobranch fossils are dominantly represented by shark and ray teeth in the geological record and can give a quick overview of the composition of the fauna. The first IAA elasmo fossils, shark teeth were described from Java (Indonesia) at the end of the 19th century, and until today, most of the publications are known from this island. In the early and middle of the 20th century, remarkable fossils were also reported from the islands of Madura (NE Java) and Sulawesi, some with detailed taxonomical descriptions. In addition, only sporadic reports on fossil occurrences exist elsewhere from the IAA, but these lack any detailed taxonomic accounts. In 2019 our research group reported a late Miocene elasmobranch fauna from Brunei (Borneo), which is now the most diverse known shallow water fossil assemblage from the entire IAA. This fauna was described from a single fossiliferous outcrop, called Ambug Hill. However, several new localities have been discovered and studied over the years, as a result the number of fossils increased, and their age range extended. Here we provide an overview of these new sites and their elasmobranch fossils, and describe remains from ten taxa among, of which eight are new to the IAA fossil record (Chiloscyllium sp., cf. Hemitriakis sp., Paragaleus sp., Carcharhinus borneensis, C. limbatus, Lamiopsis sp., Scoliodon sp., Rhinobatos sp.). The overall north Bornean elasmo assemblage is then compared with other IAA occurrences. An extended fauna list is given based on literature review and preliminary investigation of the Naturalis Biodiversity Centre collection in Leiden (The Netherlands) where most of the fossil fishes of the early explorations are stored. These assemblages are also briefly summarized, and attention is drawn to some of the unique and thus far unreported taxa (e.g., Dalatias licha). [ABSTRACT FROM AUTHOR]

Small‐scale fisheries ensure food security and employment in Angolan coastal communities. These dynamic, widespread fisheries remain mostly unregulated, with limited data available despite their likely significant impact on marine megafauna. We used an interview‐based survey to investigate local fisher interactions with elasmobranchs (sharks and rays) and gather information on utilization, trade and perceptions. All fishers (n = 83) landed elasmobranchs. Most fishers considered sharks as bycatch (74.7%, n = 62), while 100% targeted rays (Order Myliobatiformes), and 62.8% (n = 52) targeted guitarfishes (Order Rhinopristiformes). Over 80% of fishers reported declining catches and sizes of elasmobranchs over the last 30 years, raising concerns about the sustainability of these fisheries. Utilization and trade routes varied depending on elasmobranch products, with exports to China (fins) and local market sales (meat). Specifically, 8.4% (n = 5) of fishers confirmed meat and fin exports to China (4.8%, n = 3). The protection of sharks was considered by 32.5% (n = 30) of respondents, while 21.7% (n = 18) believed only certain shark species should be protected. Most respondents reported that rays (80.5%, n = 67) and guitarfishes (61%, n = 51) should not be protected. Regarding the ban on fishing, none considered it for ray species, with only 6.1% (n = 5) supporting this idea for guitarfishes. We highlight the lack of elasmobranch‐specific conservation measures and the need for a multi‐pronged approach to inform policy. Considering the scale of these fisheries, management actions need to be urgently developed and implemented to ensure the sustainability of elasmobranch fisheries while securing the livelihoods of coastal communities. [ABSTRACT FROM AUTHOR]

This article explores the reproductive behavior of bluntnose sixgill sharks in the deep sea. The researchers used remote deep-sea camera systems to observe the sharks and found evidence of mating scars on one female shark. However, they acknowledge that there could be other explanations for the scarring. The study emphasizes the need for further research on the reproductive habitats of deep-sea sharks and the importance of conservation efforts in these areas. Additionally, the article discusses the capture of a pregnant bluntnose sixgill shark in the Gulf of Tunis and highlights the importance of deep diving by large marine predators. It also emphasizes the need for diverse perspectives in deep-sea ocean field programs. [Extracted from the article]

The vertebral centra of sharks consist of cartilage, and many species' centra contain a bioapatite related to that in bone. Centra microarchitectures at the 0.5-50 µm scale do not appear to have been described previously. This study examines centrum microarchitecture in lamniform and carcharhiniform sharks with synchrotron microComputed Tomography (microCT), scanning electron microscopy and spectroscopy and light microscopy. The analysis centers on the blue shark (carcharhiniform) and shortfin mako (lamniform), species studied with all three modalities. Synchrotron microCT results from seven other species complete the report. The main centrum structures, the corpus calcareum and intermedialia, consist of fine, closely-spaced, mineralized trabeculae whose mean thicknesses and spacings range from 4.5 to 11.2 µm and 4.5 to 15.6 µm, respectively. A significant (p = 0.00001) positive linear relationship between and exists for multiple positions within one mako centrum. Carcharhiniform species' and exhibit an inverse linear relationship (p = 0.005) while in lamniforms these variables tend toward a positive relationship which does not reach statistical significance (p = 0.099). In all species, the trabeculae form an uninterrupted, interconnected network, and the unmineralized volumes are similarly interconnected. Small differences in mineralization level are observed in trabeculae. Centrum growth band pairs are found to consist of locally higher /lower mineral volume fraction. Within the intermedialia, radial canals and radial microrods were characterized, and compacted trabeculae are prominent in the mako intermedialia. The centra's mineralized central zones were non-trabecular and are also described. This study's novel result is the demonstration that the mineralized cartilage of sharks' vertebral bodies (centra) consists of a fine 3D array of interconnected plates (trabeculae) and an interpenetrating network of unmineralized tissue. This microstructure is radically different from that in tesserae or in teeth, the other main mineralized shark tissues. Using volumetric synchrotron microComputed Tomography, numerical values of mean trabecular thickness and spacing and their relationship were measured for nine species. Scanning electron microscopy added a higher resolution view of the microstructures, and histology provided complementary information on cartilage and cells. The present results suggest centra microstructure helps accommodate the very large in vivo strains and may prevent damage accumulation during millions of cycles of swimming-induced loading. [Display omitted] [ABSTRACT FROM AUTHOR]

An extensive morphometric examination of dorsal fin features for sharks belonging to the order Carcharhiniforms (families Scyliorhinidae, Triakidae, and Carcharhinidae was conducted. We compared the dorsal fin morphometric and diagnostic features of Galeus melastomus, Scyliorhinus stellaris, Galeorhinus galeus, Mustelus asterias, Mustelus mustelus, Carcharhinus altimus, C. brachyurus, C. brevipinna, C. falciformis, C. obscurus, C. plumbeus, and Prionace glauca using a mix of direct measurements and ratio-based comparisons. Fin base, height, and other ratio-based metrics provided light on the unique traits of each species, which displayed distinctive fin morphologies, particularly striking for Scyliorhinidae species with distinctive patterns and colors on their relatively big, rectangular dorsal fins. Alternatively, members of the family Triakidae have bigger, triangular fins, with varied tone and clear morphometric ratios. Lastly, the members of the family Carcharhinidae showed a wide range of fin forms and sizes, with different species displaying fin features dependent on ratios. Dorsal fin morphometric cluster analysis uncovered species-specific grouping patterns, emphasized morphological similarities and differences across families, and it was most effective within the family Scyliorhinidae. In addition, ordination methods highlighted the relationship between species and dorsal fin morphometrics by graphically representing the grouping and separation of shark species in three-dimensional areas. The significance of thorough morphometric studies in comprehending the variety and evolutionary connections within the order Carcharhiniforms was highlighted by this research, which offered a thorough foundation for the identification and classification of shark species. [ABSTRACT FROM AUTHOR]

Sertoli cells of sharks are non‐permanent components of the spermatocyst that they share exclusively with only one germ cell stage. After spermiation, all Sertoli cells, and thus the whole spent cyst, are disposed of in an area adjacent to the spermatozoal spermatocysts, that is, the resorption zone (RZ). Differences in the histology and magnitude of the RZ of the mature blue shark and Greenland shark correlate with differences in how spent cysts are dismantled. In the blue shark's RZ, the spent cyst's Sertoli nuclei were synchronously and stepwise fragmented into pyknotic bodies that were eventually resorbed in a whorl in the RZ interstitium. Conversely, cyst dismantling in the Greenland shark, that also lacked a spatially definitive RZ, revealed redundancy. One mode entailed the sloughing of the bulky Sertoli nuclei through an indistinct cyst–ductule transition area into its attached collecting ductule. A second mode entailed the asynchronous, progressive fragmentation of the bulky Sertoli nuclei into membrane‐enclosed pyknotic bodies. Both these modes solely entailed an internally coordinated demise of the spent cyst and whose basal lamina remained intact almost right to the end. Whatever the underlying mechanisms of these differences, these findings nonetheless reveal species‐specificity in the clearing up of the elasmobranch testicular parenchyma after the completion of a round of spermiogenesis. One consideration is the blue shark's expansive immune cell augmented RZ, that adjoins the animal's bone marrow equivalent tissue. The notable finding of a second conspicuous Sertoli cell type in the Greenland shark's spent cysts is also discussed. [ABSTRACT FROM AUTHOR]

'This is the story of my death'. How would the shark in Jaws (Spielberg 1975) make sense of, and respond to, the representational forms and cultural norms they are entrapped within? Would they see the story – and their role within it – in a manner akin to that the film offers to its assumed human audience? And what happens to the film, and anthropocentric understandings of it, if it is read by the eponymous shark? This creative-academic text explores these questions by imagining how a shark might respond to the ways in which American popular culture and academic discourse have represented sharks and projected different meanings onto them. [ABSTRACT FROM AUTHOR]

Our knowledge regarding the role of the microbiome in fish health has been steadily increasing in the last decade, especially for species of commercial interest. Conversely, relatively few studies focus on the microbiomes of wild fish, especially apex predators like sharks, due to lower economic interest and greater difficulty in obtaining samples. Studies investigating microbiome differences between diverse anatomical locations of sharks are limited, and the majority of the available studies are focused on the microbial diversity present on shark teeth, with the aim of preventing infections due to bites of these animals or evaluating the presence of certain pathogens in healthy or diseased specimens. Here, we investigated the skin, mouth, gills, and cloaca microbiomes of five individuals of two phylogenetically distant species of sharks (Prionace glauca and Somniosus rostratus) to obtain a better understanding of the diversity regarding the microbiomes of these animals, how they change throughout different body parts, and how much they are influenced and determined by the ecology and evolutionary relationship between host and microbiome. To confirm the taxonomy of the sharks under study, we barcoded the specimens by sequencing the mtDNA COI from a biopsy of their skin. Microbial diversity based on the 16S rRNA gene reveals that partially overlapping microbiomes inhabit different body parts of each shark species, while the communities are distinct between the two species. Our results suggest that sharks' microbiome species-specific differences are controlled by the ecology of the shark species. This is the first study comparatively analyzing the microbiome diversity of different anatomical locations in two shark species of the Mediterranean Sea. [ABSTRACT FROM AUTHOR]

The sharpnose sevengill shark (Heptranchias perlo) is a rare and poorly understood deep‐sea species, with only a few records in the Adriatic Sea over the last two centuries and a significant gap in sightings.Throughout 2023, three new records are documented in the southernmost Adriatic Sea, found at depths ranging from 391 to 452 m off Vlorë.This study marks the first comprehensive health examination of a deep‐sea shark, investigating potential trauma and injuries resulting from trawling. It encompasses pathological and histopathological examinations, supplemented by magnetic resonance imaging (MRI).The research highlights alarming post‐capture mortality rates in this data deficient species, discusses further conservation implications, and proposes protective measures for the species.Beyond addressing critical knowledge gaps, this study advocates for collaborative efforts with local fishermen to establish long‐term monitoring and obtain data on the frequency and abundance of elusive species. [ABSTRACT FROM AUTHOR]

In chondrichthyans, despite males in ex situ conservation programs exhibiting good sperm quality, offspring production is confined to specific species. This study hypothesizes that the aquarium's environmental footprint may contribute to this loss of reproductive capacity. Consequently, the research initially focused on comparing the blood metabolomic profiles of the Small-Spotted Catshark (Scyliorhinus canicula) in both an aquarium environment at Oceanogràfic of Valencia and in wild populations along the Valencia Region coast (Spain). Furthermore, the study compared the blood metabolomic profiles with those of seminal plasma. This comparison aimed to identify potential variations in seminal plasma composition and its relationship with in vitro seminal characteristics. Samples were collected from S. canicula present in the aquarium (n = 7) and wild captured individuals (n = 12). Despite conventional semen quality assessments showing no significant disparities in semen volume and sperm concentration, considerable differences were observed in sperm motility and viability rates. Specifically, aquarium specimens showed slightly reduced metrics. The untargeted metabolic study in blood revealed significant differences between aquarium and wild individuals, with 158 semi-polar and 233 non-polar differential metabolites. A parallel analysis of seminal plasma similarly revealed substantial differences, with 2 semi-polar and 74 non-polar differential metabolites. Additionally, the analysis showed 104 semi-polar and 188 non-polar metabolites shared between the blood and seminal plasma of both animal groups. A further targeted analysis of 28 metabolites in blood identified significantly lower concentrations of phenylalanine, tyrosine, lysine, taurine, arginine, N-acetyl-L-glutamate, and creatinine in aquarium sharks. In seminal plasma samples, aquarium animals exhibited elevated levels of 7-Dehydrodesmosterol but reduced levels of phenylalanine, pantothenic acid (Vit B5), and spermine. In conclusion, these findings highlight alterations in both the blood and seminal plasma metabolomic profiles between aquarium-housed and wild animals, demonstrating the impact of the aquarium's environmental footprint, which could partly explain the reduced reproductive success of sharks in captivity.

Abstract Glucose has important roles in the development of zebrafish, the vertebrate animal model; however, in most oviparous animals, the amount of maternally provided glucose in the yolk is scarce. For these reasons, developing animals need some ways to supplement glucose. Recently, it was found that developing zebrafish, a teleost fish, undergo gluconeogenesis in the yolk syncytial layer (YSL), an extraembryonic tissue that surrounds the yolk. However, teleost YSL is evolutionarily unique, and it is not clear how other vertebrates supplement glucose. In this study, we used cloudy catshark (or Torazame catshark), an elasmobranch species which possesses a YSL‐like tissue during development, and sought for possible gluconeogenic activities in this tissue. In their yolk sac, glucose increased, and our isotope tracking analysis detected gluconeogenic activities with glycerol most preferred substrate. In addition, many of gluconeogenic genes were expressed at the YSL‐like tissue, suggesting that cloudy catshark engages in gluconeogenesis in this tissue. The gluconeogenesis in teleost YSL and a similar tissue in elasmobranch species implies conserved mechanisms of yolk metabolism between these two lineages. Future studies on other vertebrate taxa will be helpful to understand the evolutionary changes in the modes of yolk metabolism that vertebrates have experienced.

IntroductionFungal diseases are frequently associated with elevated mortality rates in elasmobranchs. Currently, there is a notable absence of scientifically validated therapeutic medications that can ensure both effectiveness and safety when administered to this group of animals. The empirical prescription of azole antifungal agents, particularly voriconazole, has been posited as a potentially efficacious treatment approach for addressing most common mycoses in sharks and rays. However, there are still no published pharmacokinetic studies supporting its use in elasmobranchs and there is a lack of scientific base for its utilization in elasmobranchs.MethodsFor this study, voriconazole was administered intravenously (IV) and intramuscularly (IM), at a single dose of 4 mg/kg to six adult undulate skates (Raja undulata). A washout period of 8 weeks was left between each route of administration. Blood samples were collected both before and at ten predetermined intervals after each dosing (0.25, 0.5, 1, 1.5, 2, 4, 8, 12, 24, and 36 h after drug administration). Plasma concentrations were quantified using a validated high-performance liquid chromatography method, and pharmacokinetic (PK) data was analyzed through non-compartmental methods.ResultsThe mean extrapolated concentration at 0 h (C0) after IV administration was 27.19 ± 7.15 μg/mL and the mean peak plasma concentrations (Cmax) ± SEM after IM administration resulted 2.98 ± 0.28 μg/mL at a mean time to maximum concentration (T max) of 1.33 ± 0.17 h. Terminal half-lives were calculated and resulted 11.18 ± 1.32 h for IV injections and 9.59 ± 1.38 h for IM injections. The area under the curve extrapolated to infinity was determined as 58.14 ± 2.79 h·μg/ml following IV injections and 37.60 ± 6.67 h·μg/ml following IM injections. The IM-administered voriconazole exhibited a mean absolute bioavailability of 64.67 ± 11.47%.DiscussionThese discoveries provide backing for the possible application of voriconazole through the intramuscular route in undulate skates and support using lower dosage regimens compared to those required for oral administration, emphasizing the importance of conducting further pharmacokinetic studies with antifungals in elasmobranchs.

The exploration of fishery wastes for the extraction of value-added biocompounds has become a topic of current interest. The aim of this work was to promote a circular economy model by obtaining oil by enzymatic hydrolysis from Mustelus schmitti livers and incorporating it into bread. The oil extraction reaction was carried out using Alcalase® 2.4 L at pH 8.0, 55 °C of temperature for 60 min. Fatty acid analysis showed that the oil was rich in ω-3 long chain fatty acids (LCω3PUFAs), with the eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) being the main constituents (13 and 70 % of total PUFAs, respectively). Then, an external gelation method was developed to produce alginate capsulates loaded with the extracted oil. The encapsulation efficiency (EE) was 93.41 %. Finally, capsulated and unencapsulated fish oil were used to develop breads and more than 95 % of EPA and DHA were recovered after baking. Thus, 20 g of baked product can provide about 45 % of the recommended minimum daily intake of EPA plus DHA. The results suggest that it is possible to use the liver from the narrownose smoothhound (Mustelus schmitti) shark fishery to produce value-added products based on a circular economy.

Abstract The evolutionary origin of the jaw remains one of the most enigmatic events in vertebrate evolution. The trigeminal nerve is a key component for understanding jaw evolution, as it plays a crucial role as a sensorimotor interface for the effective manipulation of the jaw. This nerve is also found in the lamprey, an extant jawless vertebrate. The trigeminal nerve has three major branches in both the lamprey and jawed vertebrates. Although each of these branches was classically thought to be homologous between these two taxa, this homology is now in doubt. In the present study, we compared expression patterns of Hmx, a candidate genetic marker of the mandibular nerve (rV3, the third branch of the trigeminal nerve in jawed vertebrates), and the distribution of neuronal somata of trigeminal nerve branches in the trigeminal ganglion in lamprey and shark. We first confirmed the conserved expression pattern of Hmx1 in the shark rV3 neuronal somata, which are distributed in the caudal part of the trigeminal ganglion. By contrast, lamprey Hmx genes showed peculiar expression patterns, with expression in the ventrocaudal part of the trigeminal ganglion similar to Hmx1 expression in jawed vertebrates, which labeled the neuronal somata of the second branch. Based on these results, we propose two alternative hypotheses regarding the homology of the trigeminal nerve branches, providing new insights into the evolutionary origin of the vertebrate jaw.

In this study, two kinds of shark repellents, chemical shark repellent and electric pulse shark-repelling device were selected to test their effects on seawater quality as well as the physiology and survival of fish using simulated ecology experiments. Three marine fish species, Japanese flounder (Paralichthys olivaceus), black rockfish (Sebastes schlegelii), and spotted grouper (Oplegnathus punctatus) were selected as test subjects. The results of water quality indicators showed that the chemical shark repellent could significantly reduce the water transparency and pH (P < 0.05), while the electric pulse shark-repelling device had no significant effect. The mortality rate of the fishes under the chemical shark repellent was 100% within 15 min, while it was 0% under both the electric pulse shark-repelling device and the blank control. While investigating the effect of the two repellent methods on the survival and physical activities, the gills and fins of juvenile fish in the chemical shark repellent group were rapidly dyed blue reaching a mortality rate of 100% within 15 min, while the juvenile fish in the electric pulse shark-repelling device group resumed their natural activities rapidly except for exhibiting avoidance behavior when the device was started. The blood indices of the species did not show any significant differences in the chemical shark repellent group because of the acute mortality caused by poisoning. However, in the electric pulse shark-repelling device group, the number of erythrocytes and leukocytes significantly increased in all three fishes. In terms of blood biochemical indices, the chemical shark-repellents caused a significant increase in chloride content, blood glucose, and alkaline phosphatase (AKP) enzyme activity in the juvenile fishes, while the blood albumin content reduced significantly in all three fishes. The use of electric pulse shark-repelling device caused a significant increase in blood glucose and glutamate transaminase activity only in the Japanese flounder. Histopathological results showed that chemical shark repellents caused tissue damage to the gill, liver, spleen, and heart in juvenile fishes. It can be seen that compared to chemical shark repellents, the electric pulse shark-repelling device is a more environmentally friendly way to repel sharks as it has less impact on seawater quality as well as less toxic effects on major marine fishes. These results would provide a scientific basis for the selection of shark repellent methods in ocean exploration activities.

Obtaining robust estimates of population abundance is a central challenge hindering the conservation and management of many threatened and exploited species. Close‐kin mark‐recapture (CKMR) is a genetics‐based approach that has strong potential to improve the monitoring of data‐limited species by enabling estimates of abundance, survival, and other parameters for populations that are challenging to assess. However, CKMR models have received limited sensitivity testing under realistic population dynamics and sampling scenarios, impeding the application of the method in population monitoring programs and stock assessments. Here, we use individual‐based simulation to examine how unmodeled population dynamics and aging uncertainty affect the accuracy and precision of CKMR parameter estimates under different sampling strategies. We then present adapted models that correct the biases that arise from model misspecification. Our results demonstrate that a simple base‐case CKMR model produces robust estimates of population abundance with stable populations that breed annually; however, if a population trend or non‐annual breeding dynamics are present, or if year‐specific estimates of abundance are desired, a more complex CKMR model must be constructed. In addition, we show that CKMR can generate reliable abundance estimates for adults from a variety of sampling strategies, including juvenile‐focused sampling where adults are never directly observed (and aging error is minimal). Finally, we apply a CKMR model that has been adapted for population growth and intermittent breeding to two decades of genetic data from juvenile lemon sharks (Negaprion brevirostris) in Bimini, Bahamas, to demonstrate how application of CKMR to samples drawn solely from juveniles can contribute to monitoring efforts for highly mobile populations. Overall, this study expands our understanding of the biological factors and sampling decisions that cause bias in CKMR models, identifies key areas for future inquiry, and provides recommendations that can aid biologists in planning and implementing an effective CKMR study, particularly for long‐lived data‐limited species. [ABSTRACT FROM AUTHOR]

Simple Summary: The purpose of this study is to evaluate veterinary records of fish diagnosed with cancer to determine the most common presentation of this disease and the efficacy of various treatments. Currently, there are no comprehensive analyses of cancer across all fish species, and this study serves to aid veterinary clinicians in the management of these patients. Fish serve an important role in society as companion animals, educational ambassadors, and research models, and advances in their standard of care benefit veterinary medicine and several other industries. This study evaluated neoplasia in fish using medical records from zoos, aquariums, and exotic animal veterinarians. The parameters evaluated included geographic location, habitat type, signalment, anatomic location of neoplasia, type of neoplasia as confirmed with histologic examination, survival time, and treatments provided for each patient. These data were entered into the Exotic Species Cancer Research Alliance (ESCRA) database. Out of 455 cases from across the United States and England, most animals submitted were from zoologic parks or aquariums (62.9%), followed by private ownership (1.5%). The percent of female (19.3%) and male (17.8%) patients were similar, and the mean age at the time of diagnosis was 99.45 months, with a range of 12 to 300 months. The species with the highest neoplasia prevalence was koi (18.5%), followed by goldfish (10.8%). The eye was the most commonly reported site for a primary neoplasm (8.4%), and the most prevalent diagnosis across all organ systems was soft tissue sarcoma (26.2%). Only 13 patients in this study (2.9%) received any form of treatment, with a mean survival time of 8.85 months post-treatment. These data demonstrate that while information related to clinical therapy of cancer in fish species is lacking, surgical excision of tumors in fish, when feasible for the patient and client, may improve patient outcomes. [ABSTRACT FROM AUTHOR]

Studying the behavior of pelagic sharks can be challenging due to the logistical difficulties of locating migratory individuals in the open ocean. This is further compounded by their rarity in certain ocean regions due to overfishing. The accessibility of deep-water basins in The Bahamas provides a unique model system for describing how pelagic sharks connect surface and deep ocean habitats through vertical behavior. Using custom deep-sea landers in The Bahamas, we provide novel depth data for two species of pelagic sharks: a depth range extension for the dusky shark at 767 m and novel occurrence at twilight zone depth for the silky shark at 470 m. These observations expand the vertical niche for these two species, suggesting that deep diving behavior is likely more common than previously thought and likely important for ecosystem connectivity. [ABSTRACT FROM AUTHOR]

Introduction: The catecholaminergic component of the brain-pituitary-gonadal axis, which mediates the influence of external and internal stimuli on the central nervous system and gonad development in vertebrates, is largely unexplored in Chondrichthyes. We considered Scyliorhinus canicula (L., 1758) females as a model for this vertebrate's class, to assess the involvement of the catecholaminergic system of the brain in its reproduction. Along the S. canicula reproductive cycle, we characterized and evaluated differences in somata morphometry and the number of putative catecholaminergic neurons in two brain nuclei: the periventricular preoptic nucleus, hypothesized to be a positive control for ovarian development, and the suprachiasmatic nucleus, examined as a negative control. Materials andmethods: 16 S. canicula wild females were sampled and grouped in maturity stages (immature, maturing, mature, and mature egg-laying). The ovary was histologically processed for the qualitative description ofmaturity stages. Anti-tyrosine hydroxylase immunofluorescence was performed on the diencephalic brain sections. The immunoreactive somata were investigated for morphometry and counted using the optical fractionator method, throughout the confocal microscopy. Results and discussions: Qualitative and quantitative research confirmed two separate populations of immunoreactive neurons. The modifications detected in the preoptic nucleus revealed that somata were more numerous, significantly smaller in size, and more excitable during the maturing phase but decreased, becoming slightly bigger and less excitable in the egg-laying stage. This may indicate that the catecholaminergic preoptic nucleus is involved in the control of reproduction, regulating both the onset of puberty and the imminent spawning. In contrast, somata in the suprachiasmatic nucleus grew in size and underwent turnover in morphometry, increasing the total number from the immature-virgin to maturing stage, with similar values in the more advanced maturity stages. These changes were not linked to a reproductive role. These findings provide new valuable information on Chondrichthyes, suggesting the existence of an additional brain system implicated in the integration of internal and environmental cues for reproduction. [ABSTRACT FROM AUTHOR]

Comparing co-occurring species may provide insights into how aspects of ecology may play a role in influencing their microbial communities. During the 2019 commercial shrimp trawl season off coastal Georgia, swabs of skin, gills, cloaca, and gut were taken for three species of batoids (Butterfly Ray, Bluntnose Stingray, and Atlantic Stingray) and one shark species (Atlantic Sharpnose) for high-throughput sequencing of the V4 region of the bacterial 16S rRNA gene. White muscle was analyzed for stable isotopes (δ13C and δ15N) to evaluate potential niche overlap in these four sympatric mesopredators. Significant differences were found in both δ13C and δ15N signatures across species, suggesting a degree of resource partitioning. When examined within tissue type, the host species had a weak effect on β-diversity for cloaca and skin, with no differences found for gill and gut samples. However, network analysis metrics demonstrated a stronger species-specific effect and distinct microbial community relationships were apparent between the shark and batoids, with the former having tighter networks for both internally- and externally-influenced tissues (gut/cloaca and skin/gills, respectively). Despite overlapping habitat use, species' microbiomes differed in their organizational structuring that paralleled differences in stable isotope results, suggesting a mediating role of species-specific ecology on bacterial microbiomes. [ABSTRACT FROM AUTHOR]

Three species assigned to the same nominal genus of Paleozoic xenacanthiform shark have been combined with the name Orthacanthus gracilis (Chondrichthyes, Xenacanthiformes, Orthacanthidae). Orthacanthus gracilis (Giebel, 1848), which was originally combined as Chilodus gracilis Giebel, 1848, is the senior synonym; it has priority over both Orthacanthus gracilis (Newberry, 1857), which was originally combined as Diplodus gracilis Newberry, 1857, and Orthacanthus gracilis Newberry, 1875a. Proposed species-group replacement names are Orthacanthus lintonensis nom. nov. for O. gracilis (Newberry, 1857) and Orthacanthus adamas nom. nov. for O. gracilis Newberry, 1875a. Chilodus gracilis Giebel, 1848 is designated as the type species of Chilodus Giebel, 1848; this species becomes the type species for Giebelodus Whitley, 1940, which is a replacement name for Chilodus Giebel, 1848 (preoccupied by Chilodus Müller & Troschel, 1844, Actinopterygii). Giebelodus Whitley, 1940 is a junior subjective synonym of Orthacanthus Agassiz, 1843. [ABSTRACT FROM AUTHOR]

The historic collection of the Geological Survey of Alabama includes several fossil shark specimens that were recovered from the lower Paleocene Porters Creek Formation in southwestern Alabama, USA. Among these specimens are 17 teeth that we herein recognize as a new species within the extinct Paleogene genus, Palaeohypotodus. Detailed examination of these individual teeth, coupled with analyses of the dentitions of various extant lamniform sharks, allowed us to confirm monognathic and dignathic heterodonty within Palaeohypotodus. We identified upper and lower anterior and lateral tooth files that can be differentiated from one another by minor variations in morphology. Additionally, numerous isolated teeth from other Danian exposures in Alabama and Arkansas, USA , enhance our understanding of the composition of the dentition and ontogenetic heterodonty of both the new species and the genus as a whole. [ABSTRACT FROM AUTHOR]

The evolutionary origin of the jaw remains one of the most enigmatic events in vertebrate evolution. The trigeminal nerve is a key component for understanding jaw evolution, as it plays a crucial role as a sensorimotor interface for the effective manipulation of the jaw. This nerve is also found in the lamprey, an extant jawless vertebrate. The trigeminal nerve has three major branches in both the lamprey and jawed vertebrates. Although each of these branches was classically thought to be homologous between these two taxa, this homology is now in doubt. In the present study, we compared expression patterns of Hmx, a candidate genetic marker of the mandibular nerve (rV3, the third branch of the trigeminal nerve in jawed vertebrates), and the distribution of neuronal somata of trigeminal nerve branches in the trigeminal ganglion in lamprey and shark. We first confirmed the conserved expression pattern of Hmx1 in the shark rV3 neuronal somata, which are distributed in the caudal part of the trigeminal ganglion. By contrast, lamprey Hmx genes showed peculiar expression patterns, with expression in the ventrocaudal part of the trigeminal ganglion similar to Hmx1 expression in jawed vertebrates, which labeled the neuronal somata of the second branch. Based on these results, we propose two alternative hypotheses regarding the homology of the trigeminal nerve branches, providing new insights into the evolutionary origin of the vertebrate jaw. [ABSTRACT FROM AUTHOR]

Dextrocardia is a rare congenital malformation in humans in which most of the heart mass is positioned in the right hemithorax rather than on the left. The heart itself may be normal and dextrocardia is sometimes diagnosed during non‐related explorations. A few reports have documented atypical positions of the cardiac chambers in farmed teleost fish. Here, we report the casual finding of a left–right mirrored heart in an 85 cm long wild‐caught spiny dogfish (Squalus acanthias) with several organ malformations. Macroscopic observations showed an outflow tract originating from the left side of the ventricular mass, rather than from the right. Internal inspection revealed the expected structures and a looped cavity. The inner curvature of the loop comprised a large trabeculation, the bulboventricular fold, as expected. The junction between the sinus venosus and the atrium appeared normal, only mirrored. MRI data acquired at 0.7 mm isotropic resolution and subsequent 3D‐modeling revealed the atrioventricular canal was to the right of the bulboventricular fold, rather than on the left. Spurred by the finding of dextrocardia in the shark, we revisit our previously published material on farmed Adriatic sturgeon (Acipenser naccarii), a non‐teleost bony fish. We found several alevins with inverted (left‐loop) hearts, amounting to an approximate incidence of 1%–2%. Additionally, an adult sturgeon measuring 90 cm in length showed abnormal topology of the cardiac chambers, but normal position of the abdominal organs. In conclusion, left–right mirrored hearts, a setting that resembles human dextrocardia, can occur in both farmed and wild non‐teleost fish. [ABSTRACT FROM AUTHOR]

Background: Coprolites, i.e., fossilized faeces, are an important source of knowledge on the diet and food processing mechanisms in the fossil record. Direct and indirect evidences for the dietary preferences of extinct sharks are rare in the fossil record. The first coprolite attributable to Ptychodus containing prey remains from the European Cretaceous is documented here. Methods: A coprolite from the Late Cretaceous of Opole (southern Poland) was scanned using micro-computed tomography to show the arrangement of the inclusions. In addition, the cross-section was examined under the SEM/EDS to analyse the microstructure and chemical composition of the inclusions. Results: Brachiopod shell fragments and foraminiferan shells are recognized and identified among the variously shaped inclusions detected through the performed analysis. Conclusions: The extinct shell-crushing shark Ptychodus has been identified as the likely producer of the examined coprolite. The presence of brachiopod shell fragments indicates that at least some species of this durophagous predatory shark may have preyed on small benthic elements on the sea bottom. [ABSTRACT FROM AUTHOR]

Background: Elasmobranch populations are declining, predominantly driven by overfishing, and over a third of global sharks, rays, and chimeras are estimated to be threatened with extinction. In terms of trade, Brazil is ranked the eleventh-largest shark producer and the top importer of shark meat in the world. Research has shown that elasmobranchs are sold in Brazil under the name "cação" (a generic designation for cartilaginous fish) to overcome consumer resistance. Methodology and results: This study used DNA barcoding to investigate the sale of sharks in the State of São Paulo during the COVID-19 lockdown. A total of 35 samples of "cação" were analysed, revealing six different shark species on sale, including Carcharhinus falciformis, Carcharhinus signatus, Carcharias taurus, Isurus oxyrinchus, and Isurus paucus, that are threatened with extinction according to the IUCN red list. This study demonstrates that vulnerable elasmobranchs are being commercialised under the label "cação" in the São Paulo State and Brazil. Conclusions: Comparison of shark products traded before and during the COVID-19 pandemic showed no significant difference, suggesting lockdown did not affect patterns of species commercialisation. Effective fisheries and sale monitoring, correct product labelling legislation and increased consumer awareness that "cação" is shark are needed for appropriate conservation and management of shark populations in Brazil. [ABSTRACT FROM AUTHOR]

International trade in croaker swim bladders or maws and incidental catches in fisheries targeting croakers for their maws pose a global problem that needs addressing to protect target croakers and globally threatened small cetaceans, sharks, rays and marine turtles.The lesson of the likely imminent extinction of the vaquita porpoise (Phocoena sinus) in the Gulf of California, Mexico, owing to entanglement in gillnets targeting the totoaba croaker for its maw, is that the underlying threats to marine species must be addressed well before precipitous declines make their extinction inevitable.Opportunistic interviews with fishers and fish traders in Bangladesh indicate that the increasing demand for fish maws, selling for as much as 5,000 USD per kg, may be intensifying small‐scale coastal fisheries and bycatches of globally threatened marine wildlife, especially due to the potential for a windfall profit.In 137 croaker catches made in gillnets, sharks were bycaught in 22%, marine turtles in 8% and rays in 3% of catches. Of particular concern were six bycatches of 125 Critically Endangered scalloped hammerhead sharks (Sphyrna lewini), 11 bycatches of 20 Vulnerable (VU) olive ridley turtles (Lepidochelys olivacea) and two bycatches of 13 VU longtail butterfly rays (Gymnura poecilura).A recent IUCN Motion for 'Controlling and monitoring trade in croaker swim bladders to protect target croakers and reduce incidental catches of threatened marine megafauna' recommends conducting an analysis on the impacts of the demand for and trade in fish maws on croaker species and threatened marine megafauna, regulating trade in fish maws through national laws and developing a potential proposal to list croaker species in the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).To prevent species extinctions, additional measures focusing on fishery management will be needed. [ABSTRACT FROM AUTHOR]

This study describes a new species belonging to the genus Cathetocephalus from the spinner shark Carcharhinus brevipinna off the coast of Yucatan, Mexico. Cathetocephalus badilloi n. sp. has a soft scolex transversely positioned to the long axis of the strobila. The scolex is composed of an apical pad, papillate band and rugose base. The papillate band has two papillary segments; the upper segment has numerous papillae, positioned one next to the other in an irregular and heterogeneous way with a spongy texture that remains along the band. The lower papillary segment has numerous papillae positioned one next to the other, without space between them. This papillary band presents flattened rectangular papillae with a division located at the top of each the papilla, giving it the appearance of a molar tooth. Using the 28S rDNA gene and the method of Maximum Likelihood (ML) for phylogenetic analysis, we identified the present material as a new species. We did not collect specimens with mature or gravid proglottids, but since the specific identification of the members of this genus is based on the characteristics of the scolex, our proposal of the new species is determined by the morphology of this organ as well as the molecular results obtained.

Chondrichthyans comprise a diverse group of vertebrate species with extraordinary ecological relevance. Yet, multiple members of this evolutionary lineage are associated with significant extinction risk. The sailfin roughshark Oxynotus paradoxus is a deep-water benthic shark currently listed as vulnerable due to population declines in parts of its range. Here we provide the first complete mitochondrial genome of O. paradoxus, comprising also the first record for the genus and family Oxynotidae. These data can facilitate future monitoring of the genetic diversity in this and related species. Genomic DNA was extracted from O. paradoxus collected in the eastern North Atlantic off western Portugal (37.59°N, 9.51°W) and sent for Illumina Paired-End (2 × 150 bp) library construction and whole genome sequencing on a Novaseq6000 platform. Trimmomatic (version 0.38) was used to remove adapters and MitoZ (version 3.4) to assemble and annotate the mitogenome. This mitogenome with 17 100 bp has a total of 38 genes, 13 of which are protein-coding genes, 23 transfer RNA genes, and 2 ribosomal RNA genes. Eight transfer RNAs and 1 protein-coding gene (NADH dehydrogenase subunit 6, NAD6) are in the complementary strand. In the provided phylogenetic inference, with all available and verified Squalomorphii mitogenomes, the four orders are well separated, and as expected, O. paradoxus is placed in the Squaliformes order. This data reinforces the need for more genomic resources for the Oxynotidae family.

1. One-third of elasmobranch species are threatened with extinction, and the precise assessment of their sperm parameters and quality is one stage in the development of reproductive technology for animal conservation. 2. Computer-Assisted Sperm Analysis (CASA) is the gold standard for sperm analysis; however, there were not one setup established for elasmobranchs. 3. This study presents the description of a specific setup developed for elasmobranch semen analysis using the CASA system. 4. In addition, it provides a gold-standard technique protocol for elasmobranch sperm quality assessment. 5. The described setup presented an accuracy of more than 90 percent in fourteen distinct species of freshwater and marine sharks, stingrays, and rays, failing only when there were two or more bundled sperm.

IntroductionThe catecholaminergic component of the brain-pituitary-gonadal axis, which mediates the influence of external and internal stimuli on the central nervous system and gonad development in vertebrates, is largely unexplored in Chondrichthyes. We considered Scyliorhinus canicula (L., 1758) females as a model for this vertebrate's class, to assess the involvement of the catecholaminergic system of the brain in its reproduction. Along the S. canicula reproductive cycle, we characterized and evaluated differences in somata morphometry and the number of putative catecholaminergic neurons in two brain nuclei: the periventricular preoptic nucleus, hypothesized to be a positive control for ovarian development, and the suprachiasmatic nucleus, examined as a negative control.Materials and methods16 S. canicula wild females were sampled and grouped in maturity stages (immature, maturing, mature, and mature egg-laying). The ovary was histologically processed for the qualitative description of maturity stages. Anti-tyrosine hydroxylase immunofluorescence was performed on the diencephalic brain sections. The immunoreactive somata were investigated for morphometry and counted using the optical fractionator method, throughout the confocal microscopy.Results and discussionsQualitative and quantitative research confirmed two separate populations of immunoreactive neurons. The modifications detected in the preoptic nucleus revealed that somata were more numerous, significantly smaller in size, and more excitable during the maturing phase but decreased, becoming slightly bigger and less excitable in the egg-laying stage. This may indicate that the catecholaminergic preoptic nucleus is involved in the control of reproduction, regulating both the onset of puberty and the imminent spawning. In contrast, somata in the suprachiasmatic nucleus grew in size and underwent turnover in morphometry, increasing the total number from the immature-virgin to maturing stage, with similar values in the more advanced maturity stages. These changes were not linked to a reproductive role. These findings provide new valuable information on Chondrichthyes, suggesting the existence of an additional brain system implicated in the integration of internal and environmental cues for reproduction.

CD4 and LAG-3 are related molecules that are receptors for MHC class II molecules. Their major functional differences are situated in their cytoplasmic tails, in which CD4 has an activation motif and LAG-3 an inhibitory motif. Here, we identify shark LAG-3 and show that a previously identified shark CD4-like gene has a genomic location, expression pattern, and motifs similar to CD4 in other vertebrates. In nurse shark (Ginglymostoma cirratum) and cloudy catshark (Scyliorhinus torazame), the highest CD4 expression was consistently found in the thymus whereas such was not the case for LAG-3. Throughout jawed vertebrates, the CD4 cytoplasmic tail possesses a Cx(C/H) motif for binding kinase LCK, and the LAG-3 cytoplasmic tail possesses (F/Y)xxL(D/E) including the previously determined FxxL inhibitory motif resembling an immunoreceptor tyrosine-based inhibition motif (ITIM). On the other hand, the acidic end of the mammalian LAG-3 cytoplasmic tail, which is believed to have an inhibitory function as well, was acquired later in evolution. The present study also identified CD4-1, CD4-2, and LAG-3 in the primitive ray-finned fishes bichirs, sturgeons, and gars, and experimentally determined these sequences for sterlet sturgeon (Acipenser ruthenus). Therefore, with CD4-1 and CD4-2 already known in teleosts (modern ray-finned fish), these two CD4 lineages have now been found within all major clades of ray-finned fish. Although different from each other, the cytoplasmic tails of ray-finned fish CD4-1 and chondrichthyan CD4 not only contain the Cx(C/H) motif but also an additional highly conserved motif which we expect to confer a function. Thus, although restricted to some species and gene copies, in evolution both CD4 and LAG-3 molecules appear to have acquired functional motifs besides their canonical Cx(C/H) and ITIM-like motifs, respectively. The presence of CD4 and LAG-3 molecules with seemingly opposing functions from the level of sharks, the oldest living vertebrates with a human-like adaptive immune system, underlines their importance for the jawed vertebrate immune system. It also emphasizes the general need of the immune system to always find a balance, leading to trade-offs, between activating and inhibiting processes.

Background Coprolites, i.e., fossilized faeces, are an important source of knowledge on the diet and food processing mechanisms in the fossil record. Direct and indirect evidences for the dietary preferences of extinct sharks are rare in the fossil record. The first coprolite attributable to Ptychodus containing prey remains from the European Cretaceous is documented here. Methods A coprolite from the Late Cretaceous of Opole (southern Poland) was scanned using micro-computed tomography to show the arrangement of the inclusions. In addition, the cross-section was examined under the SEM/EDS to analyse the microstructure and chemical composition of the inclusions. Results Brachiopod shell fragments and foraminiferan shells are recognized and identified among the variously shaped inclusions detected through the performed analysis. Conclusions The extinct shell-crushing shark Ptychodus has been identified as the likely producer of the examined coprolite. The presence of brachiopod shell fragments indicates that at least some species of this durophagous predatory shark may have preyed on small benthic elements on the sea bottom.

The inaugural Computer Vision for Marine Scientists workshop was held at the 17th South African Marine Science Symposium, with the primary goal of establishing a community of practice for computer vision (CV) in marine sciences in South Africa. The one-day hybrid event, attended by 97 people, covered the principles of artificial intelligence (AI) techniques required for evaluating video and photographic imagery through presentations, practical demonstrations and interactive discussions. The recordings of the workshop sessions are available online, providing an opportunity to reach marine researchers both regionally and globally. The workshop highlighted that many scientists have begun to incorporate CV and AI into their research activities; however, there is little national coordination and the extent of research is lagging behind international trends. To support image-based AI research in South Africa, it is critical to maintain and expand the network established during the workshop. This would enable a more collaborative and successful approach to incorporating CV technology in the country's marine research initiatives, ultimately leading to ground-breaking discoveries and advancements in the field. [ABSTRACT FROM AUTHOR]