From screens to seas: Tech contaminants in tiger sharks.

The potential negative impacts of Technology-Critical Elements (TCEs) on the environment and wildlife, despite increasingly recognized, remain largely overlooked. In this sense, this study aimed to investigate the concentrations of several TCEs, including rubidium (Rb), titanium (Ti) and various Rare Earth Elements (REEs), in different tissues of tiger sharks. Sharks incidentally caught by artisanal fleets in southern Brazil were opportunistically sampled and liver, gills, kidneys, heart, muscle, eyes, brain, skin, and teeth were analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Significant Rb concentration variations were observed across different tissues, with higher levels detected in kidneys and lower levels in the liver. Titanium concentrations also exhibited significant differences, with higher levels detected in teeth and lower levels in liver. Although no statistical differences were observed for the analyzed REEs, a trend of higher accumulation in the liver, gills, and skin was noted. Light Rare Earth Elements (LREEs) were found predominantly in all organs, with neodymium, lanthanum, and cerium as the most significant REEs detected. Several statistically significant correlations were identified between Rb and REEs, as well as between Ti and REEs, indicating systemic transport of these elements across different tissues. These findings indicate that the growing extraction and disposal of metallic elements, driven by technological advancements, may lead to their assimilation by marine fauna, particularly at higher trophic levels. The potential harmful effects on these organisms remain unknown and require urgent investigation. Additionally, as mining activities intensify globally, precise legislative measures are essential to address environmental concerns, species conservation, and human health considerations.

Accumulation of Per- and Polyfluoroalkyl Substances (PFAS) in Coastal Sharks from Contrasting Marine Environments: The New York Bight and The Bahamas.

Per- and polyfluoroalkyl substances (PFAS) enter the marine food web, accumulate in organisms, and potentially have adverse effects on predators and consumers of seafood. However, evaluations of PFAS in meso-to-apex predators, like sharks, are scarce. This study investigated PFAS occurrence in five shark species from two marine ecosystems with contrasting relative human population densities, the New York Bight (NYB) and the coastal waters of The Bahamas archipelago. The total detected PFAS (∑PFAS) concentrations in muscle tissue ranged from 1.10 to 58.5 ng g-1 wet weight, and perfluorocarboxylic acids (PFCAs) were dominant. Fewer PFAS were detected in Caribbean reef sharks (Carcharhinus perezi) from The Bahamas, and concentrations of those detected were, on average, ∼79% lower than in the NYB sharks. In the NYB, ∑PFAS concentrations followed: common thresher (Alopias vulpinus) > shortfin mako (Isurus oxyrinchus) > sandbar (Carcharhinus plumbeus) > smooth dogfish (Mustelus canis). PFAS precursors/intermediates, such as 2H,2H,3H,3H-perfluorodecanoic acid and perfluorooctanesulfonamide, were only detected in the NYB sharks, suggesting higher ambient concentrations and diversity of PFAS sources in this region. Ultralong-chain PFAS (C ≥ 10) were positively correlated with nitrogen isotope values (δ15N) and total mercury in some species. Our results provide some of the first baseline information on PFAS concentrations in shark species from the northwest Atlantic Ocean, and correlations between PFAS, stable isotopes, and mercury further contextualize the drivers of PFAS occurrence.

Whale shark Rhyncodon typus exposure to organochlorine pesticides in the Southern Gulf of California, Mexico.

Organochlorine pesticides (OCPs) are persistent organic pollutants (POPs), characterized by their high mobility and environmental persistence, bioaccumulation, and trophic transfer. Considering the highly migratory nature and longevity of the whale shark, this species can be considered as an early warning bioindicator of regional contamination from the marine environment. This work investigated the concentration of twenty OCPs in thirty whale shark skin biopsies, collected between 2014 and 2015 in Bahía La Paz (Gulf of California, Mexico). Mean detected OCP levels were 33.99 ± 105.23 ng/g dw (dry weight), and ΣChlordane, ΣDrin, and ΣHCH showed the highest concentrations. Statistically differences in mean OCP concentration were not found by sex and size. PC1 and PC2 accounted for 68.1 % and 16.1 % of the total variance, respectively. The presence of higher levels of some pesticides than their corresponding metabolites suggests recent applications related to agricultural activity in the surrounding areas of Baja California peninsula.

Revealing Spermatogenesis in Smooth-Hound Sharks Mustelus mustelus: Insights into the Morphological and Macromolecular Composition of Spermatogenic Cells.

Elasmobranchs have an ancestral reproductive system, which offers insights into vertebrate reproductive evolution. Despite their unchanged design over 400 million years, they evolved complex mechanisms ensuring reproductive success. However, human activities induced a significant decline in elasmobranch populations worldwide. In the Mediterranean basin, the smooth-hound shark (Mustelus mustelus) is one of the species that are considered vulnerable to human activities. Conservation efforts necessitate a thorough understanding of its reproductive strategy. This study focused on mature male specimens of smooth-hound sharks that were captured in the Adriatic area and successively analyzed to provide, for the first time, a histologically detailed description of testicular development in the species. Seven phases of the spermatogenesis process were identified, along with the macromolecular characterization of cells obtained using Fourier-transform infrared imaging. Histological analysis showed structural and cellular features similar to those documented in the spermatocysts of other elasmobranchs. The examination of the evolution and migration of both germinative and Sertoli cells at each phase revealed their close connection. Furthermore, different expression levels of lipids, proteins, and phosphates (DNA) at each spermatogenesis stage were observed. This research provided new information on spermatogenesis in the common smooth-hound shark, which is crucial for conservation efforts against population decline and anthropogenic pressures.

Bioaccumulated trace element toxicity in commercially harvested bronze whaler sharks (Carcharhinus brachyurus) of South Africa.

Shark meat consumption may pose a significant risk to human health as high levels of toxic pollutants bioaccumulate in muscular tissue. Commercial harvest of Carcharhinus brachyurus meat in South Africa is estimated at 100-300 filleted tons per annum. Muscle tissue samples from 41 sharks were collected from the southern and eastern coastlines of South Africa in 2022 and analysed for 10 trace elements and 8 polychlorinated biphenyl congeners. All trace elements were found to be lower than the regulatory maximum limits for human consumption in most samples irrespective of shark length, sex, and sampling region. However, the estimated daily intake for Mercury and Arsenic exceeded the oral reference dose set by international agencies. The meat from this shark may be consumed due to its low toxic potential for human health, however long-term exposure to C. brachyurus meat should be avoided as it could pose detrimental health risks to consumers.

Unique hepatic maternal transfer pattern of trace metals and perfluoroalkyl substances (PFAS) in a bluntnose sixgill shark (Hexanchus griseus).

The fate and distribution of environmental contaminants includes bioaccumulation within marine organisms. A deceased 4-m long adult female bluntnose sixgill shark, pregnant with 72 pups, was recovered from Coles Bay on Vancouver Island, BC, Canada in 2019. This specimen provided a unique opportunity to examine maternal transfer of contaminants in a yolk-sac viviparous shark species. Liver subsamples of the adult and offspring were analyzed for 18 targeted inorganic elements by inductively coupled plasma optical emission spectroscopy (ICP-OES) and 21 targeted perfluoroalkyl substances (PFAS) by liquid chromatography-electrospray ionization-high resolution mass spectrometry (LC-ESI-Orbitrap MS). The maternal-offspring transfer efficiencies in liver tissue were subsequently examined for both contaminant classes. Concentrations of all detectable metals apart from calcium and magnesium were found to be higher in the mother compared to the offspring, including substantial levels of toxic cadmium (6 ± 2 mg kg-1 dw) and lead (7 ± 3 mg kg-1 dw). Conversely, high maternal transfer efficiencies were observed for PFAS (i.e., ΣPFAS = 71 ± 9 ng g-1 ww in offspring compared to 13 ± 9 ng g-1 ww in the mother). This study highlighted the unique maternal transfer characteristics of PFAS in bluntnose sixgill sharks depending on the structure of the polar head group, with greater liver-to-liver transfer efficiencies observed for perfluorocarboxylic acids (PFCAs) than perfluorosulfonic acids (PFSAs) of the same fluorocarbon chain length.

Gluconeogenesis in the yolk syncytial layer-like tissue of cloudy catshark (Scyliorhinus torazame).

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.

Development of branchial ionocytes in embryonic and larval stages of cloudy catshark, Scyliorhinus torazame.

In teleost fish, branchial ionocytes are important sites for osmoregulation and acid-base regulation by maintaining ionic balance in the body fluid. During the early developmental stages before the formation of the gills, teleost ionocytes are localized in the yolk-sac membrane and body skin. By comparing with teleost fish, much less is known about ionocytes in developing embryos of elasmobranch fish. The present study investigated the development of ionocytes in the embryo and larva of cloudy catshark, Scyliorhinus torazame. We first observed ionocyte distribution by immunohistochemical staining with anti-Na+/K+-ATPase (NKA) and anti-vacuolar-type H+-ATPase (V-ATPase) antibodies. The NKA- and V-ATPase-rich ionocytes appeared as single cells in the gill filaments from stage 31, the stage of pre-hatching, while the ionocytes on the body skin and yolk-sac membrane were also observed. From stage 32, in addition to single ionocytes on the gill filaments, some outstanding follicular structures of NKA-immunoreactive cells were developed to fill the inter-filament region of the gill septa. The follicular ionocytes possess NKA in the basolateral membrane and Na+/H+ exchanger 3 in the apical membrane, indicating that they are involved in acid-base regulation like single NKA-rich ionocytes. Three-dimensional analysis and whole-mount immunohistochemistry revealed that the distribution of follicular ionocytes was limited to the rostral side of gill septum. The rostral sides of gill septum might be exposed to faster water flow than caudal side because the gills of sharks gently curved backward. This dissymmetric distribution of follicular ionocytes is considered to facilitate efficient body-fluid homeostasis of catshark embryo.

Heavy metals and trace minerals in commonly available shark species from North East Arabian Sea: A human health risk perspective.

Shark is a seafood commodity that is a good source of minerals and accumulates heavy metals and trace elements through biomagnification, which can pose health risk if taken above the permissible limit. A study was conducted on commonly landed eleven shark species (Scoliodon laticaudus, Rhizopriodon oligolinx, Sphyrna lewini (CR), Carcharhinus macloti, Carcharinus limbatus, Carcharhinus amblyrhynchoides, Carcharhinus sorrah, Carcharinus falciformes(VU), Glaucostegus granulatus, Chiloscyllium arabicum, Loxodon macrorhinus) and analyzed for their heavy metal content, Hazard Index, Total Hazard Quotient, Metal Pollution Index, and also calculated the health risk associated with the consumption. Most of the heavy metals and trace minerals were found to be within the acceptable limit. The Targeted Hazard Quotient (THQ) and the Hazard Index (HI) of all the species except two were less than 1 (HI ≤ 1.0). The Metal Pollution Index (MPI) is showing either no impact or very low contamination. An overall study on hazard identification and health risk characterization in terms of heavy metals shows contamination of some heavy metals in sharks, but there is no potential human health risk associated with consumption.

Exceptionally high levels of total mercury in deep-sea sharks of the Southeastern Mediterranean sea over the last ∼ 40 years.

Deep-sea habitats are currently recognized as a hot spot for mercury (Hg) accumulation from anthropogenic sources, resulting in elevated concentrations of total mercury (THg) in deep-sea megafauna. Among them, deep-sea sharks (Class Chondrichthyes) are characterized by high trophic position and extended longevity and are, therefore, at high risk for mercury contamination. Despite this, sharks are overexploited by fishing activity in increasingly deeper water, worldwide, imposing health risks to human consumption. While it is imperative to better understand long-term mercury contamination in deep-sea megafauna, few historical data sets exist to capture this process. Here we explore four decades (1985-2022) of THg accumulation in five species of deep-sea sharks (G. melastomus, E. spinax, S. rostratus, C. granulosus, and D. licha) of the ultra-oligotrophic Southeastern Mediterranean Sea (SEMS) sampled during 19 research cruises. We exhibited exceptionally high THg levels (per length/weight), the highest as 16.6 µg g-1 (wet wt.), almost entirely (98.9 %; n = 298 specimens) exceeding the limit for safe consumption (0.3-0.5 µg THg g-1 wet wt.). The maximal THg levels of the long-lived species D. licha and C. granulosus in the SEMS were enriched by a factor of âˆ¼ 7 and >10 compared to counterpart species from other oceanic areas, respectively. We attribute this to the ultra-oligotrophic conditions of the SEMS, which cause slower growth rates and dwarfism in deep-sea sharks, resulting in an extended exposure time to mercury contamination. In the long-lived species, C. granulosus and D. licha, a temporal increase of average THg levels of âˆ¼ 80 % was recorded between 1987-1999 and 2021-2022. This likely reflects the long-term accumulation of historical anthropogenic Hg in deep-sea environments, which is further amplified in marginal seas such as the Mediterranean, impacted by global air pollution crossroads and surrounded by land-based pollution sources. Future consumption of products from deep-sea sharks is potentially high risk to human health.

The Rectal Gland of the Shark: The Road to Understanding the Mechanism and Regulation of Transepithelial Chloride Transport.

Pictured, described, and speculated on, for close to 400 years, the function of the rectal gland of elasmobranchs remained unknown. In the late 1950s, Burger discovered that the rectal gland of Squalus acanthias secreted an almost pure solution of sodium chloride, isosmotic with blood, which could be stimulated by volume expansion of the fish. Twenty five years later, Stoff discovered that the secretion of the gland was mediated by adenyl cyclase. Studies since then have shown that vasoactive intestinal peptide (VIP) is the neurotransmitter responsible for activating adenyl cyclase; however, the amount of circulating VIP does not change in response to volume expansion. The humoral factor involved in activating the secretion of the gland is C-type natriuretic peptide, secreted from the heart in response to volume expansion. C-type natriuretic peptide circulates to the gland where it stimulates the release of VIP from nerves within the gland, but it also has a direct effect, independent of VIP. Sodium, potassium, and chloride are required for the gland to secrete, and the secretion of the gland is inhibited by ouabain or furosemide. The current model for the secretion of chloride was developed from this information. Basolateral NaKATPase maintains a low intracellular concentration of sodium, which establishes the large electrochemical gradient for sodium directed into the cell. Sodium moves from the blood into the cell (together with potassium and chloride) down this electrochemical gradient, through a coupled sodium, potassium, and two chloride cotransporter (NKCC1). On activation, chloride moves from the cell into the gland lumen, down its electrical gradient through apical cystic fibrosis transmembrane regulator. The fall in intracellular chloride leads to the phosphorylation and activation of NKCC1 that allows more chloride into the cell. Transepithelial sodium secretion into the lumen is driven by an electrical gradient through a paracellular pathway. The aim of this review was to examine the history of the origin of this model for the transport of chloride and suggest that it is applicable to many epithelia that transport chloride, both in resorptive and secretory directions.

Maternal transfer of trace elements to shark eggs and their dietary assimilation efficiencies.

Dogfish (Scyliorhinus canicula) transferred trace elements (110Ag, 109Cd, 54Mn and 75Se) from their diet to eggs, and their components (yolk and embryo, case and jelly) at greatly varying rates. Trace element levels in eggs showed positive linear relationships (p < 0.001; r2-0.83-0.91) with their cumulative rates of maternal ingestion over 61 days (maternal-to-egg transfer rates: mTFs). These mTFs varied by 2-3 orders of magnitude, with 54Mn > 110Ag > 75Se > 109Cd, and their range encompassed those previously measured for 60Co, 65Zn, 241Am and 134Cs. For six of the eight trace elements, their mTFs were significantly influenced (p < 0.05; r2 = 0.72) by both their dietary assimilation efficiency and their location within the egg (case). In contrast, both 110Ag and 54Mn greatly exceeded the mTFs predicted by this multiple regression model by one and 2-3 orders of magnitude, respectively, and were predominantly transferred to the egg case. Among elements, contrasting rates of transfer and percentage distributions in egg components imply differing ecotoxicological and radiological detriments to the developing embryo.

Development of Shark Single Domain Antibodies Specific for Human α-Fetoprotein and the Multimerization Strategy in Serum Detection.

Sensitive detection of cancer biomarkers can contribute to the timely diagnosis and treatment of diseases. In this study, the whitespotted bamboo sharks were immunized with human α-fetoprotein (AFP), and a phage-displayed variable new antigen receptor (VNAR) single domain antibody library was constructed. Then four unique VNARs (VNAR1, VNAR11, VNAR21, and VNAR25) against AFP were isolated from the library by biopanning for the first time. All of the sequences belong to type II of VNAR, and the VNAR11 was much different from the rest of the three sequences. Then VNAR1 and VNAR11 were selected to fuse with the C4-binding protein α chain (C4bpα) sequence and efficiently expressed in the Escherichia coli system. Furthermore, a VNAR-C4bpα-mediated sandwich chemiluminescence immunoassay (VSCLIA) was developed for the detection of AFP in human serum samples. After optimization, the VSCLIA showed a limit of detection of 0.74 ng/mL with good selectivity and accuracy. Moreover, the results of clinical serum samples detected by the VSCLIA were confirmed by an automatic immunoanalyzer in the hospital, indicating its practical application in actual samples. In conclusion, the novel antibody element VNAR exhibits great potential for immunodiagnosis, and this study also provides a new direction and experimental basis for AFP detection.

Health Benefits of Oily Fish: Illustrated with Blue Shark (Prionace glauca), Shortfin Mako Shark (Isurus oxyrinchus), and Swordfish (Xiphias gladius).

Oily fish is a rich source of energy, proteins, essential amino acids, lipids, vitamins, and minerals. Among the macronutrients with the highest contribution are lipids, mainly long-chain omega 3 polyunsaturated fatty acids (ω-3 LC-PUFA), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Both EPA and DHA play a beneficial role in promoting health and preventing many diseases, including cardiovascular diseases, such as stroke and acute myocardial infarction. They also contribute to the prevention of neurological, metabolic, and immune-system-related diseases, as well as supporting body-weight control. Oily fish consumption is also important at different stages of human life, from conception to old age. For example, DHA plays an important role in brain and retina development during fetal development and in the first two years of life, as it positively influences neurodevelopment, such as visual acuity, and cognitive functions. In contrast with the possible health benefits of the intake of oily fish, the presence of certain chemical pollutants, for example, heavy metals, can be a risk for the health of consumers, mainly in sensitive population groups such as pregnant women and children under 2 years of age. The presence of these pollutants is influenced to a greater extent by fish species, their role in the trophic chain, and their size. However, various studies state that the benefits outweigh the risk of consuming certain species. This review will be focused on the health benefits of the intake of three oily fish species, namely blue shark (Prionace glauca), shortfin mako shark (Isurus oxyrinchus), and swordfish (Xiphias gladius).

Succinate-mediated reactive oxygen species production in the anoxia-tolerant epaulette (Hemiscyllium ocellatum) and grey carpet (Chiloscyllium punctatum) sharks.

Anoxia/re-oxygenation (AR) results in elevated unchecked oxidative stress and mediates irreversible damage within the brain for most vertebrates. Succinate accumulation within mitochondria of the ischaemic brain appears to increase the production of reactive oxygen species (ROS) upon re-oxygenation. Two closely related elasmobranchs, the epaulette shark (Hemiscyllium ocellatum) and the grey carpet shark (Chiloscyllium punctatum) repeatedly experience near anoxia and re-oxygenation in their habitats and have adapted to survive AR at tropical temperatures without significant brain injuries. However, these anoxia-tolerant species display contrasting strategies to survive AR, with only H. ocellatum having the capacity to supress metabolism and H. ocellatum mitochondria the capacity to depress succinate oxidation post-AR. We measured oxygen consumption alongside ROS production mediated by elevated succinate in mitochondria of permeabilized cerebellum from both shark species. Although mitochondrial respiration remained similar for both species, the ROS production in H. ocellatum was half that of C. punctatum in phosphorylating and non-phosphorylating mitochondria. Maximum ROS production in H. ocellatum was mediated by succinate loads 10-fold higher than in C. punctatum mitochondria. The contrasting survival strategies of anoxia-tolerant sharks reveal the significance of mitigating ROS production under elevated succinate load during AR, shedding light on potential mechanisms to mitigate brain injury.

Assessment of potential risks to human health associated with trace elements in three commercially important shark species captured in the Central Mexican Pacific.

Shark meat is a popular protein source worldwide. However, existing national control policies for ensuring the safety and quality of shark meat are minimal. There are concerns about the sustainability of shark populations, which bioaccumulate and biomagnify potentially toxic elements at higher rates than non-predatory fish, posing a risk to human health. In this study, the contributions of essential elements to the Recommended Dietary Allowance (RDA) and potentially toxic elements to the Reference Dose (RfD) linked to shark consumption (200 g per week) were investigated for three shark species in the Central Mexican Pacific. We estimated risks and benefits for women, children, and men. Our results suggest that the three shark species are sources of Se, Co, Cr, Cu, Fe, and Zn, but poor sources of Mn for women and men aged 19-50 years. A weekly ingestion of 200 g of shark meat exceeded the RfD-As by 4-14 times and the RfD-Pb by 1.1-1.7 times for adults, indicating a potential risk to human health. The three shark species were also significant sources of potentially toxic elements for children, including Hg, Cd, Cr, and Pb. An excessive intake of Se was observed, with levels at 8.4-10.6 and 4.3-5.3 times the RDA for children aged 1-8 and 9-13 years, respectively. Although shark meat can be a good source of essential nutrients, the lack of controls in the commercialization process indicates that it should be consumed in moderation due to the potential risks associated with excessive exposure to potentially toxic elements. This caution is particularly important for children and pregnant women, who are at higher risk of health complications from consuming contaminated food.

Elemental analysis of vertebrae discerns diadromous movements of threatened non-marine elasmobranchs.

River sharks (Glyphis spp.) and some sawfishes (Pristidae) inhabit riverine environments, although their long-term habitat use patterns are poorly known. We investigated the diadromous movements of the northern river shark (Glyphis garricki), speartooth shark (Glyphis glyphis), narrow sawfish (Anoxypristis cuspidata), and largetooth sawfish (Pristis pristis) using in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) on vertebrae to recover elemental ratios over each individual's lifetime. We also measured elemental ratios for the bull shark (Carcharhinus leucas) and a range of inshore and offshore stenohaline marine species to assist in interpretation of results. Barium (Ba) was found to be an effective indicator of freshwater use, whereas lithium (Li) and strontium (Sr) were effective indicators of marine water use. The relationships between Ba and Li and Ba and Sr were negatively correlated, whereas the relationship between Li and Sr was positively correlated. Both river shark species had elemental signatures indicative of prolonged use of upper-estuarine environments, whereas adults appear to mainly use lower-estuarine environments rather than marine environments. Decreases in Li:Ba and Sr:Ba at the end of the prenatal growth zone of P. pristis samples indicated that parturition likely occurs in fresh water. There was limited evidence of prolonged riverine habitat use for A. cuspidata. The results of this study support elemental-environment relationships observed in teleost otoliths and indicate that in situ LA-ICP-MS elemental characterization is applicable to a wide range of elasmobranch species as a discriminator for use and movement across salinity gradients. A greater understanding of processes that lead to element incorporation in vertebrae, and relative concentrations in vertebrae with respect to the ambient environment, will improve the applicability of elemental analysis to understand movements across the life history of elasmobranchs into the future.

Analysis of Toxic Metals Found in Shark Fins Collected from a Global Trade Hub.

As human activities release increasingly more fossil fuel-derived emissions directly into the atmosphere, terrestrial, aquatic, or marine ecosystems, the biomagnification and bioaccumulation of toxic metals in seafood is an ever more pressing concern. As apex predators, sharks are particularly susceptible to biomagnification and bioaccumulation. The consumption of shark fin is frequent throughout Asia, and their ingestion represents a pathway through which human exposure to potentially unsafe levels of toxic metals can occur. Shark fins processed for sale are difficult, if not impossible to identify to the species level by visual methods alone. Here, we DNA-barcoded 208 dried and processed fins and in doing so, identified fourteen species of shark. Using these identifications, we determined the habitat of the shark that the fin came from and the concentrations of four toxic metals (mercury, arsenic, cadmium, and lead) in all 208 samples via inductively coupled plasma mass spectrometry. We further analyzed these concentrations by habitat type, either coastal or pelagic, and show that toxic metal concentrations vary significantly between species and habitat. Pelagic species have significantly higher concentrations of mercury in comparison to coastal species, whereas coastal species have significantly higher concentrations of arsenic. No significant differences in cadmium or lead concentrations were detected between pelagic or coastal species. Our results indicate that a number of analyzed samples contain toxic metal concentrations above safe human consumption levels.

An Ancient MHC-Linked Gene Encodes a Nonrearranging Shark Antibody, UrIg, Convergent with IgG.

Gnathostome adaptive immunity is defined by the Ag receptors, Igs and TCRs, and the MHC. Cartilaginous fish are the oldest vertebrates with these adaptive hallmarks. We and others have unearthed nonrearranging Ag receptor-like genes in several vertebrates, some of which are encoded in the MHC or in MHC paralogous regions. One of these genes, named UrIg, was detected in the class III region of the shark MHC that encodes a protein with typical V and C domains such as those found in conventional Igs and TCRs. As no transmembrane region was detected in gene models or cDNAs, the protein does not appear to act as a receptor. Unlike some other shark Ig genes, the UrIg V region shows no evidence of RAG-mediated rearrangement, and thus it is likely related to other V genes that predated the invasion of the RAG transposon. The UrIg gene is present in all elasmobranchs and evolves conservatively, unlike Igs and TCRs. Also, unlike Ig/TCR, the gene is not expressed in secondary lymphoid tissues, but mainly in the liver. Recombinant forms of the molecule form disulfide-linked homodimers, which is the form also detected in many shark tissues by Western blotting. mAbs specific for UrIg identify the protein in the extracellular matrix of several shark tissues by immunohistochemistry. We propose that UrIg is related to the V gene invaded by the RAG transposon, consistent with the speculation of emergence of Ig/TCR within the MHC or proto-MHC.

The allometric scaling of oxygen supply and demand in the California horn shark, Heterodontus francisci.

The gill surface area of aquatic ectotherms is thought to be closely linked to the ontogenetic scaling of metabolic rate, a relationship that is often used to explain and predict ecological patterns across species. However, there are surprisingly few within-species tests of whether metabolic rate and gill area scale similarly. We examined the relationship between oxygen supply (gill area) and demand (metabolic rate) by making paired estimates of gill area with resting and maximum metabolic rates across ontogeny in the relatively inactive California horn shark, Heterodontus francisci. We found that the allometric slope of resting metabolic rate was 0.966±0.058 (±95% CI), whereas that of maximum metabolic rate was somewhat steeper (1.073±0.040). We also discovered that the scaling of gill area shifted with ontogeny: the allometric slope of gill area was shallower in individuals <0.203 kg in body mass (0.564±0.261), but increased to 1.012±0.113 later in life. This appears to reflect changes in demand for gill-oxygen uptake during egg case development and immediately post hatch, whereas for most of ontogeny, gill area scales in between that of resting and maximum metabolic rate. These relationships differ from predictions of the gill oxygen limitation theory, which argues that the allometric scaling of gill area constrains metabolic processes. Thus, for the California horn shark, metabolic rate does not appear limited by theoretical surface-area-to-volume ratio constraints of gill area. These results highlight the importance of data from paired and size-matched individuals when comparing physiological scaling relationships.