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Vertebrate remains are scarce in the Cretaceous of Iran, with only a few records of fishes and one genus of chelonioid turtle known from the Dariyan and Sarvak formations. Here, we describe for the first time the paleoichthyological fauna of the Kazhdumi Formation, based on disarticulated microremains that represent the first record of vertebrates in the unit, highlighting this novel Albian–Cenomanian fossil assemblage. The fauna is composed of lamniform (cf. Dallasiella sp., cf. Paranomotodon sp., Anacoracidae indet., cf. Haimirichia amonensis, cf. Scapanorhynchus, Lamniformes indet.) sharks and pycnodontiforms Osteichthyes. [ABSTRACT FROM AUTHOR]

Many of the egg cases of oviparous chondrichthyans remain unknown and undescribed in the literature. Egg cases can be a useful taxonomic character for species distinction and can be a valuable indicator of a species distribution in the field. In this study, the egg cases for 9 of the 10 nominal species of Heterodontus are described and compared, and the terminology and methodology for studying them are standardized. Heterodontus egg cases are distinct and easily identifiable from other oviparous egg cases by having a unique corkscrew shape formed by a pair of lateral keels spiraling along its length. Heterodontus egg cases range between 7.5 and 14.5 cm in egg case length, 3.7 and 5.8 cm in egg case width at midportion, and have 0.75–4 complete rotations. Morphometric measurements of egg cases from the nine species were subjected to multivariate analysis, with unique characters enabling distinction between them. Egg cases can be separated into three morphotypes: the “wide keels lacking tendrils” group, the “narrow keels with tendrils” group, and the “wide keels with tendrils” group. The egg case of Heterodontus ramalheira remains unknown. [ABSTRACT FROM AUTHOR]

The capture of a rare, critically endangered adult angular rough shark, Oxynotus centrina (Linnaeus, 1758), with abnormal coloration is reported in this paper. The shark exhibited a partial reduction in pigmentation, resulting in an overall pale appearance with white‐greyish patches. Since the retinal pigmentation appeared normal, the shark was considered leucistic. This represents the first documented case of leucism in this species and the first colour disorder reported in the family Oxynotidae Gill, 1912. Despite the atypical appearance, the physical health of the shark seemed unaffected, supporting the notion that pigment disorders in deep‐sea sharks do not inherently impair survival and growth. Full morphometric characteristics are presented and compared with those of a normal individual of the same sex caught in the same area, showing no differences. [ABSTRACT FROM AUTHOR]

Mortality resulting from interactions with fishing gears represent an important threat to sensitive species globally. In this study, we address this issue by defining five species groups of marine megafauna (marine mammals, seabirds, demersal and pelagic elasmobranchs, and sea turtles), and conducting a productivity-susceptibility analysis (PSA) within the context of data-limited fisheries in the Mediterranean and Black Sea. Although there are significant differences among species within each group, this approach has been considered much more direct and functional for management purposes. The productivity (P) of each species group was determined by evaluating a set of attributes averaged across representative species within each group. Species groups' susceptibility (S) to bycatch was assessed through a comprehensive review of existing literature and expert judgment, considering a series of semi-quantitative attributes. Our analysis identified areas and fishing gears posing potential risks to the species groups assessed, highlighting that sea turtles and elasmobranchs face the potential risk of incidental captures from various fishing gears operating in both neritic (bottom trawls, set nets and bottom longlines) and pelagic (drifting longlines) environments. Marine mammals exhibit moderate risk across most fishing gears, with particular concern for the harbour porpoise Phocoena phocoena relicta in the Black Sea, primarily due to the interaction with set nets, which can severely impact entire population even capturing few specimens due the species low productivity. Seabirds face reduced impact with fishing activities, irrespective of the type of gear examined or the specific area under investigation. Overall, our study highlights the specific basins and fishing gears requiring focused management measures, mitigation strategies, and enhanced monitoring activities to mitigate the impacts of bycatch on vulnerable marine megafauna. [ABSTRACT FROM AUTHOR]

The evolution of ion channel clustering at nodes of Ranvier enabled the development of complex vertebrate nervous systems. At mammalian nodes, the K+ leak channels TRAAK and TREK-1 underlie membrane repolarization. Despite the molecular similarities between nodes and the axon initial segment (AIS), TRAAK and TREK-1 are reportedly node-specific, suggesting a unique clustering mechanism. However, we show that TRAAK and TREK-1 are enriched at both nodes and AIS through a common mechanism. We identified a motif near the C-terminus of TRAAK that is necessary and sufficient for its clustering. The motif first evolved among cartilaginous fish. Using AnkyrinG (AnkG) conditional knockout mice, CRISPR/Cas9-mediated disruption of AnkG, co-immunoprecipitation, and surface recruitment assays, we show that TRAAK forms a complex with AnkG and that AnkG is necessary for TRAAK’s AIS and nodal clustering. In contrast, TREK-1’s clustering requires TRAAK. Our results expand the repertoire of AIS and nodal ion channel clustering mechanisms and emphasize AnkG’s central role in assembling excitable domains. [ABSTRACT FROM AUTHOR]

The first record of bramble sharks (Echinorhinus brucus) in the United Arab Emirates is presented. In situ observations of multiple bramble sharks were made at depths between 460 and 720 m from two piloted submersibles and a remotely operated vessel, representing the first known observations of this species in its native deep-water habitat in Arabia and the Indian Ocean. Notably, this research expands on the documented regional distribution of E. brucus for the Gulf of Oman/Arabian Sea and extends this species' regional records to deeper mesophotic zones. These findings underscore the need for further research to understand the ecology and distribution of this cryptic shark species, particularly given its global endangered status and the limited knowledge of its regional population dynamics. [ABSTRACT FROM AUTHOR]

Estimating and understanding the ratio between effective population size (Ne) and census population size (Nc) are pivotal in the conservation of large marine pelagic fish species, including bony fish such as tunas and cartilaginous fish such as sharks, given the challenges associated with obtaining accurate estimates of their abundance. The difficulties inherent in capturing and monitoring these species in vast and dynamic marine environments often make direct estimation of their population size challenging. By focusing on Ne, it is conceivable in certain cases to approximate census size once the Ne/Nc ratio is known, although this ratio can vary and does not always increase linearly, as it is influenced by various ecological and evolutionary factors. Thus, this ratio presents challenges and complexities in the context of pelagic species conservation. To delve deeper into these challenges, firstly, we recall the diverse types of effective population sizes, including contemporary and historical sizes, and their implications in conservation biology. Secondly, we outline current knowledge about the influence of life history traits on the Ne/Nc ratio in the light of examples drawn from large and abundant pelagic fish species. Despite efforts to document an increasing number of marine species using recent technologies and statistical methods, establishing general rules to predict Ne/Nc remains elusive, necessitating further research and investment. Finally, we recall statistical challenges in relating Ne and Nc emphasizing the necessity of aligning temporal and spatial scales. This last part discusses the roles of generation and reproductive cycle effective population sizes to predict genetic erosion and guiding management strategies. Collectively, these sections underscore the multifaceted nature of effective population size estimation, crucial for preserving genetic diversity and ensuring the long‐term viability of populations. By navigating statistical and theoretical complexities, and addressing methodological challenges, scientists should be able to advance our understanding of the Ne/Nc ratio. [ABSTRACT FROM AUTHOR]

For the live-bearing and egg-laying class of chondrichthyan fishes a three parameter logistic 'maternity' function with a variable upper asymptote, PMax, can be used to predict the average probability of a female giving birth or laying eggs in a season. Although fundamental to calculating the reproductive capacity of a population, few studies report maternity functions, with maturity functions often used as a proxy. Applying logistic models to simulated and empirical data showed that it was feasible to estimate PMax from maternal data and that accuracy, bias, and confidence interval coverage often improved compared to when a fixed value was used. However, sample sizes of 100–200 maternal females were typically required for accurate estimation of PMax. While maturity parameters could be estimated with greater accuracy, substituting them for maternity parameters overestimated lifetime reproductive output. Greater use of maternity functions has the potential to improve calculation of reproductive output in quantitative populations models. In addition to improvements in parameter estimation, this method involves fewer assumptions and enables statistical inferences to be made on frequency of reproduction. [ABSTRACT FROM AUTHOR]

The upper part of the Harudi Formation of the Kutch basin in Gujarat, western India, has recently yielded a heretofore undocumented assemblage of elasmobranchs, including extinct sand tiger sharks Brachycarcharias lerichei and Striatolamia macrota, extinct tiger sharks Galeocerdo eaglesomei and G. clarkensis, requiem shark Carcharhinus mancinae, as well as sawfish Pristis sp. A bony fish taxon represented by Trichiurus sp. was also recovered. After a 43-years gap, this study provides a taxonomic update on the middle Eocene sharks of Kutch. Their coexistence with the larger benthic foraminifera Nummulites obtusus and planktonic foraminifera Orbulinoides beckmanni dates this fish fauna to 40–41.03 Ma, which corresponds to the time frame of the Bartonian transgression and extreme warming event Middle Eocene Climatic Optimum (MECO). The MECO elasmobranch assemblage of Kutch comes from shelf settings with bathymetry of 30–60 m, and it differs from those associated with Paleocene–Eocene hyperthermal events and deposited in the bay complex. It seems that G. clarkensis and C. mancinae emerged in Kutch during MECO. The global stratigraphic distribution demonstrates that B. lerichei and S. macrota originated in North America, and their appearance in Kutch expands their geographic range into the eastern Tethys realm, possibly as a result of MECO-linked Bartonian/Kirther transgression. [ABSTRACT FROM AUTHOR]

Vertebrate fossils from Aotearoa New Zealand have revealed the global significance of Zealandia on the origins of modern birds, the history of cetaceans during major climatic events of the Cenozoic and the evolution of cartilaginous and ray-finned fish. Internationally important collections of vertebrate fossils are housed in collections across Aotearoa and have attracted researchers from around the world studying evolution, biogeography and climate change. This special issue of the Journal of the Royal Society of New Zealand celebrates the vertebrate fossils of Aotearoa by showcasing taonga (treasures) that are significant to global and local vertebrate history. [ABSTRACT FROM AUTHOR]

While dorsal-ventrally compressed chondrichthyans are among the most imperiled fishes in the world, there is still limited knowledge of the biology of many of these species, even in well-studied ocean basins. In the western North Atlantic Ocean, the population structure of the Atlantic angel shark (Squatina dumeril) is not fully understood; therefore, the portioning of genetic variation was assessed among individuals caught along the east coast of the United States (Atlantic) and on the northern Gulf of Mexico (Gulf) using reduced representation genomics and mitochondrial sequencing. Three distinct groups were delineated with nuclear data, the Atlantic, the eastern Gulf, and the western Gulf, along boundaries described by previous research. Mitochondrial data only resolved two groups, with the western Gulf separated from the eastern Gulf and Atlantic combined. Demographic modeling suggested that the Atlantic population separated from a single Gulf population which subsequently split into eastern and western populations. Additionally, there was evidence that adjacent populations experienced gene flow after splitting, which may explain the incongruence between results based on nuclear and mtCR data. Correlations between environmental variables and allele frequencies at 873 loci indicated potential local adaptation. Therefore, the preservation of all three groups is necessary for the conservation of long-term adaptive variation important for species persistence. [ABSTRACT FROM AUTHOR]

A new genus and species of kitefin sharks (Squaliformes: Dalatiidae), Danodalatias ochevi gen. et sp. nov., is described based on isolated teeth from the lower part of the Berezovaya Strata (Lower Paleocene, Danian Stage) in the vicinity of the farmstead of Rasstrigin (Volgograd Region). The teeth of Centroselachus goordi Mannering et Hiller, 2008 from the Paleocene of New Zealand are reclassified here as Danodalatias goordi (Mannering et Hiller, 2008) comb. nov. The association of these two species with a bipolar distribution into the genus Danodalatias gen. nov. suggests that kitefin sharks (Dalatiidae) were globally distributed back in the Early Cenozoic and inhabited both shallow epicontinental and relatively deep ocean shelf environments during that time. [ABSTRACT FROM AUTHOR]

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Single-domain antibodies, including variable domains of the heavy chains of heavy chain-only antibodies (VHHs) from camelids and variable domains of immunoglobulin new antigen receptors (VNARs) from cartilaginous fish, show the therapeutic potential of targeting antigens in a cytosol reducing environment. A large proportion of single-domain antibodies contain non-canonical cysteines and corresponding non-canonical disulfide bonds situated on the protein surface, rendering them vulnerable to environmental factors. Research on non-canonical disulfide bonds has been limited, with a focus solely on VHHs and utilizing only cysteine mutations rather than the reducing agent treatment. In this study, we examined an anti-lysozyme VNAR and an anti-BC2-tag VHH, including their non-canonical disulfide bond reduced counterparts and non-canonical cysteine mutants. Both the affinity and stability of the VNARs and VHHs decreased in the non-canonical cysteine mutants, whereas the reduced-state samples exhibited decreased thermal stability, with their affinity remaining almost unchanged regardless of the presence of reducing agents. Molecular dynamics simulations suggested that the decrease in affinity of the mutants resulted from increased flexibility of the CDRs, the disappearance of non-canonical cysteine–antigen interactions, and the perturbation of other antigen-interacting residues caused by mutations. These findings highlight the significance of non-canonical cysteines for the affinity of single-domain antibodies and demonstrate that the mutation of non-canonical cysteines is not equivalent to the disruption of non-canonical disulfide bonds with a reducing agent when assessing the function of non-canonical disulfide bonds. [ABSTRACT FROM AUTHOR]

Developing frameworks to identify knowledge gaps and prioritize research on diet studies in marine fish species is critical, as this knowledge is required for ecosystem-based management. We applied a framework in central Patagonia, Argentina, which faces a demand for gap assessments in diet knowledge and ecosystem management due to changes in marine fish assemblages' structure and function linked to industrial fishing and tropicalization. Our framework effectively identified gaps by examining the history of research efforts regarding spatial and temporal coverage, sampling sizes, fish life stages, and information quality of studies per species. We found critical gaps in local diet studies, particularly for mostly bony, Petromyzonti, and Myxini species, whereas elasmobranchs received the best coverage of the diet described. Most studies lack evaluation of ontogenetic diet changes and prey cumulative curves. Fixing these shortcomings improves research quality and reduces data uncertainties in community assessments. The prioritization framework identified high-priority species as those that require updated diet information, had shifted ranges, and lacked data. Our framework can be tailored to other biological traits and regions based on specific contextual needs to identify research gaps and priorities for fish assemblages impacted by global change while disseminating knowledge from diverse sources and languages. [ABSTRACT FROM AUTHOR]

Summary The study of antibodies in jawed vertebrates (gnathostomes) provides every immunologist with a bird's eye view of how human immunoglobulins (Igs) came into existence and subsequently evolved into their present forms. It is a fascinating Darwinian history of conservation on the one hand and flexibility on the other, exemplified by the Ig heavy chain (H) isotypes IgM and IgD/W, respectively. The cartilaginous fish (e.g., sharks) Igs provide a glimpse of “how everything got off the ground,” while the amphibians (e.g., the model Xenopus) reveal how the adaptive immune system made an about face with the emergence of Ig isotype switching and IgG‐like structure/function. The evolution of mucosal Igs is a captivating account of malleability, convergence, and conservation, and a call to arms for future study! In between there are spellbinding chronicles of antibody evolution in each class of vertebrates and rather incredible stories of how antibodies can adapt to occupy niches, for example, single‐domain variable regions, cold‐adapted Igs, convergent mechanisms to dampen antibody function, provision of mucosal defense, and many more. The purpose here is not to provide an encyclopedic examination of antibody evolution, but rather to hit the high points and entice readers to appreciate how things “came to be.” [ABSTRACT FROM AUTHOR]

Elucidating cellular architecture and cell-type evolution across species is central to understanding immune system function and susceptibility to disease. Adaptive immunity is a shared trait of the common ancestor of cartilaginous and bony fishes. However, evolutionary features of lymphocytes in these two jawed vertebrates remain unclear. Here, we present a single-cell RNA sequencing atlas of immune cells from cartilaginous (white-spotted bamboo shark) and bony (zebrafish and Chinese tongue sole) fishes. Cross-species comparisons show that the same cell types across different species exhibit similar transcriptional profiles. In the bamboo shark, we identify a phagocytic B cell population expressing several pattern recognition receptors, as well as a T cell sub-cluster co-expressing both T and B cell markers. In contrast to a division by function in the bony fishes, we show close linkage and poor functional specialization among lymphocytes in the cartilaginous fish. Our cross-species single-cell comparison presents a resource for uncovering the origin and evolution of the gnathostome immune system. Both cartilaginous and bony fishes have adaptive immune cells, but the evolutionary features of these diverse cell populations remain understudied. Here the authors report single-cell RNA sequencing atlas of both species to define these features and to find reduced evolutionary diversification of immune cells in cartilaginous fishes. [ABSTRACT FROM AUTHOR]

The taxonomic status of butterfly rays within the genus Gymnura remains a subject of ongoing debate among researchers. Some authors recognize up to five valid species for the Americas, while others considered several to be synonyms, which has posed a persistent challenge. We aimed to shed light on this complexity by employing molecular operational taxonomic units (MOTUs) based on the mitochondrial gene cytochrome oxidase I (COI). Genetic sequences were obtained from fresh muscle tissue collected in the marine ecoregions corresponding to the type locality from all the nominal butterfly ray species distributed along the Eastern Tropical Pacific (ETP). Our results unveiled compelling findings; all the species delimitation models used consistently identified seven MOTUs for the American continent and an extra G. altavela MOTU restricted to Africa. In addition, our results and models exceeded the worldwide accepted interspecific threshold of 2.0%. Remarkably, our results support the taxonomic reinstatement of Gymnura afuerae (Hildebrand, 1946) as a valid species, with a range expanding into the ETP in the Southern Hemisphere. Similarly, our data support the recent suggestion of resurrecting Gymnura valenciennii (Duméril, 1865) as a valid species in the western Atlantic. These findings urge a reassessment of the conservation status and a comprehensive taxonomic revision of American butterfly rays. [ABSTRACT FROM AUTHOR]

The family Potamotrygonidae is part of the Neotropical ichthyofauna and has the largest diversity of freshwater elasmobranchs in the world. The neurocranium in Potamotrygonidae is an elongated and dorsoventrally flattened structure that articulates anterolaterally with the anterior portion of the propterygium, posteriorly with the sinarcual, and posterolaterally with the hyomandibula. This anatomical structure is comparatively described in Potamotrygonidae in an effort to reveal new phylogenetically relevant characters. Additionally, a new genus-level phylogeny of the family is proposed herein based on 60 novel morphological characters. The subfamily Potamotrygoninae, whose monophyly is well sustained by previous studies, is further supported herein by a variable number of cranial synapomorphies (up to 17), depending on the optimization adopted. Furthermore, we also recovered Potamotrygon and Plesiotrygon as consecutive sister-groups to a clade including Heliotrygon and Paratrygon. The neurocranium of potamotrygonids and its anatomical variation is also discussed in the context of previous morphological and molecular phylogenies of Neotropical freshwater stingrays. [ABSTRACT FROM AUTHOR]

The original UT-1 transporter gene was initially identified in the spiny dogfish (Squalus acanthias), but localization of the UT-1 protein was not determined. Subsequent UT-1 expression was shown to localize to the collecting tubule (CT) of the shark nephron in other shark species, with expression in a closely related chimaera species also located additionally at a lower level in the intermediate-I segment (IS-I) of the nephron. In spiny dogfish, two UT-1 splice variants are known (UT-1 long and short), and there was also a second UT-1 gene described (here termed Brain UT). In this study, a second splice variant of the second Brain UT gene was discovered. Expression profiles (mRNA) of UT-1 long and short and Brain UT were determined in a number of spiny dogfish tissues. Quantitative PCR in kidney samples showed that the level of the short variant of UT-1 was around 100 times higher than the long variant, which was itself expressed around 10 times higher than Brain UT cDNA/mRNA (in kidney). For the long variant, there was a significantly higher level of mRNA abundance in fish acclimatized to 75% seawater. Ultimately, three UT-1 antibodies were made that could bind to both the UT-1 short and long variant proteins. The first two of these showed bands of appropriate sizes on Western blots of around 52.5 and 46 kDa. The second antibody had some additional lower molecular weight bands. The third antibody was mainly bound to the 46 kDa band with faint 52.5 kDa staining. Both the 52.5 and 46 kDa bands were absent when the antibodies were pre-blocked with the peptide antigens used to make them. Across the three antibodies, there were many similarities in localization but differences in subcellular localization. Predominantly, antibody staining was greatest in the intermediate segment 1 (IS-I) and proximal (PIb) segments of the first sinus zone loop of the nephron, with reasonably strong expression also found at the start and middle of the late distal tubule (LDT; second sinus zone loop). While some expression in the collecting tubule (CT) could not be ruled out, the level of staining seemed to be low or non-existent in convoluted bundle zone nephron segments such as the CT. Hence, this suggests that spiny dogfish have a fundamentally different mode of urea absorption in comparison to that found in other shark species, potentially focused more on the nephron sinus zone loops than the CT. [ABSTRACT FROM AUTHOR]

Simple Summary: Before calcification, the early skeletal development of both Homo sapiens and the chondrichthyan fish Raja asterias is exclusively cartilaginous. This cartilage is formed through tissue segmentation and chondrocyte mitoses. Mineral deposition in the cartilage matrix influences the stiffness and shape of the skeletal segments. In mammals, calcified cartilage serves as a scaffold for bone deposition, which is then remodeled. Conversely, chondrichthyans retain calcified cartilage as their skeletal structure, forming calcification nuclei or "tesserae". These structures adapt to aquatic locomotion. In mammals, endochondral ossification provides limb bones with the necessary stiffness for terrestrial locomotion. X-rays of marine mammals show how endochondral ossification in dolphin flippers adapts to aquatic demands, including shortening of certain bones and an increase in elements in the autopodium's central rays. Before calcification begins, the early embryonic and fetal skeletal development of both mammalian Homo sapiens and the chondrichthyan fish Raja asterias consists exclusively of cartilage. This cartilage is formed and shaped through processes involving tissue segmentation and the frequency, distribution, and orientation of chondrocyte mitoses. In the subsequent developmental phase, mineral deposition in the cartilage matrix conditions the development further. The stiffness and structural layout of the mineralized cartilage have a significant impact on the shape of the anlagen (early formative structure of a tissue, a scaffold on which the new bone is formed) and the mechanical properties of the skeletal segments. The fundamental difference between the two studied species lies in how calcified cartilage serves as a scaffold for osteoblasts to deposit bone matrix, which is then remodeled. In contrast, chondrichthyans retain the calcified cartilage as the definitive skeletal structure. This study documents the distinct mineral deposition pattern in the cartilage of the chondrichthyan R. asterias, in which calcification progresses with the formation of focal calcification nuclei or "tesserae". These are arranged on the flat surface of the endo-skeleton (crustal pattern) or aligned in columns (catenated pattern) in the radials of the appendicular skeleton. This anatomical structure is well adapted to meet the mechanical requirements of locomotion in the water column. Conversely, in terrestrial mammals, endochondral ossification (associated with the remodeling of the calcified matrix) provides limb bones with the necessary stiffness to withstand the strong bending and twisting stresses of terrestrial locomotion. In this study, radiographs of marine mammals (reproduced from previously published studies) document how the endochondral ossification in dolphin flippers adapts to the mechanical demands of aquatic locomotion. This adaptation includes the reduction in the length of the stylopodium and zeugopodium and an increase in the number of elements in the autopodium's central rays. [ABSTRACT FROM AUTHOR]

Isolated teeth of two janassid petalodonts collected from cave passages within the Middle Mississippian (Viséan) Joppa Member of the Ste. Genevieve Formation at Mammoth Cave National Park, Kentucky represents the first record of this group of chondrichthyans from this formation. A new janassid, Strigilodus tollesonae, gen et sp. nov., is recognised from isolated teeth, representing all tooth families, and are characterised by their rounded spoonlike cusps and V- to U-shaped lingual cristae. Janassa sp. is also present within the Joppa Member of the Ste. Genevieve Formation. Dental reconstructions are proposed for Strigilodus tollesonae and Cypripediodens cristatus, modelled after previous observations for Janassa dentitions. Strigilodus had a dental arrangement more similar to Janassa, while Cypripediodens was uniquely adapted for a possible extreme form of durophage feeding. We propose that within Janassidae, there were two unnamed subfamilies with Janassa and Strigilodus forming the Janassinae, while Cholodus, Cypripediodens, and Cavusodus forming Cholodinae subfam. nov. [ABSTRACT FROM AUTHOR]

Over one third of sharks, rays and chimaeras (chondrichthyans) are threatened with extinction globally. In the Mediterranean Sea, more than half of chondrichthyan species face this risk, although a variety of international, regional, and national rules and regulations apply directly and indirectly targeting management and conservation for these species. In this work, we provide an overview of relevant legislation and policies in the region, which regulate, inter alia, commercial fisheries, while highlighting through cases studies how implementation in practice at national level looks like. Horizontal gaps and inconsistencies that hinder chondrichthyan management in the region are also illustrated. Furthermore, we present recommendations for improvement and additional tools that can be used, even if not originally or explicitly targeting chondrichthyans, for improving the management of these taxa in the Mediterranean. [ABSTRACT FROM AUTHOR]

Aim: Modern sharks are a diverse and highly threatened group playing important roles in ecosystems. They have an abundant fossil record spanning at least 250 million years (Myr), consisting primarily of isolated teeth. Throughout their evolutionary history, sharks have faced multiple environmental changes and extinction events. Here, we aim to use dental characters to quantify how shark functional diversity has changed during the last 66 Myr. Location: Global. Time period: Cenozoic era (66–0 million years ago; Ma). Major taxa studied: Sharks (Selachii). Methods: We complied a dataset of over 9000 shark teeth belonging to 537 taxa from museum collections and scientific literature and measured six dental characters strongly linked with functional traits. We then quantified different functional diversity metrics across Cenozoic time bins, compared them against null expectations and identified the most important taxa contributing to maintaining functional diversity. Results: Sharks displayed relatively high functional diversity during the Cenozoic, with 66%–87% of the functional space being occupied for ~60 Myr (Palaeocene to Miocene). High levels of functional redundancy during this time resulted in larger‐than‐expected functional richness; but a large decline (−45%) in redundancy in the Oligocene (~30 Ma) left shark functional diversity highly vulnerable to further loss. Shark functional diversity declined from the late Miocene (~10 Ma) onwards, losing 44% of functional richness by the Recent. Extinct sharks disproportionally contributed to the Cenozoic functional diversity and spanned a wider range of functional space than extant sharks, with the loss of mid‐sized suction feeders and large‐bodied predators driving functional declines. Main conclusions: After maintaining high levels of functional diversity for most of the Cenozoic, sharks lost nearly half of their functional diversity in the last ~10 Myr. Current anthropogenic pressures are therefore likely eroding an already diminished shark functional diversity, leaving future communities ecologically deprived compared with their thriving geological past. [ABSTRACT FROM AUTHOR]

The shortfin mako shark (Isurus oxyrinchus) is a large pelagic predator that inhabits coastal and ocean waters. It has several teeth arranged in rows that run from the rostral to the lingual face. These teeth are in several stages of maturation, where the teeth closest to the rostral face are more mature and functional and the teeth closest to the lingual face are still in development. The tooth supply of the shark is unlimited throughout its life. The mechanism of tooth replacement follows that, when the front teeth are discarded physiologically, the posterior teeth replace it. This study us used a head and dental arch of I. oxyrinchus. Intraoral radiographs were obtained with the aim to show details of the pulp cavity. The study concluded that the pulp diameter varies according to the stage of dental maturation. [ABSTRACT FROM AUTHOR]

An increasing onus on elasmobranch management by regional bodies has been hindered by a lack of data on abundance, distribution and fisheries, especially in data‐poor areas like the eastern Atlantic Ocean. From 2015 through 2017, 204 baited remote underwater videos (BRUV) were deployed in Cabo Verde around the eastern islands of Sal, Boavista and Maio and the remote offshore reef João Valente to establish a baseline of elasmobranch abundance. Over 200 hours of footage revealed 215 individual elasmobranchs, spanning 14 species from 6 taxonomic families. The abundance of elasmobranchs was highest in Maio, the island with the smallest human population, followed by Boavista and Sal. Smaller‐bodied meso‐predatory species such as the common smoothhound (Mustelus mustelus) and the Atlantic weasel shark (Paragaleus pectoralis) constituted the majority of observations in Maio and Boavista. Inversely, Carcharhinus spp. were observed in considerably greater abundance in Sal, and there was notably lower abundance of small‐bodied sharks at sites with high large‐bodied Carcharhinid abundance. Species richness was consistent with abundance estimates across islands, with Boavista and Sal recording the highest species diversity, followed by Maio. Results suggest that amongst Cabo Verde's eastern islands, there exists a high relative diversity and abundance of coastal elasmobranchs compared to populations in West Africa. Nonetheless, there is evidence of exploitation of higher trophic levels species. This trend is most notable in the decreasing abundance of Carcharhinids with increasing proximity to the capital city Praia, suggesting that fishing efforts from the capital are negatively affecting the abundance of large‐bodied, higher‐trophic predators. [ABSTRACT FROM AUTHOR]

Many species of shark are threatened with extinction, a consequence of overfishing to supply the shark fin and meat trade, or through bycatch. While the shark fin trade is comparatively well understood and documented, the trade in shark meat is remains understudied, even though it is larger than the fin trade in terms of value and volume. The species composition of the shark meat trade along with their geographic origin of capture remains largely unknown; this is problematic because it makes the design of effective conservation measures to prevent the overexploitation of sharks and the associated loss of biodiversity challenging. Our work here is the first to comprehensively survey of the shark meat trade in retail establishments from a region of the world that has global significance in the shark product trade. It suggests that local fishing pressure on one or few stocks or populations, rather than complex international supply chains support the trade in shark meat products destined for human consumption. Importantly, it provides a critical assessment and documentation of the species involved. This work has relevance in our efforts to protect sharks and arrest the ongoing biodiversity crisis. [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]

The taxonomic status of butterfly rays within the genus Gymnura remains a subject of ongoing debate among researchers. Some authors recognize up to five valid species for the Americas, while others considered several to be synonyms, which has posed a persistent challenge. We aimed to shed light on this complexity by employing molecular operational taxonomic units (MOTUs) based on the mitochondrial gene cytochrome oxidase I (COI). Genetic sequences were obtained from fresh muscle tissue collected in the marine ecoregions corresponding to the type locality from all the nominal butterfly ray species distributed along the Eastern Tropical Pacific (ETP). Our results unveiled compelling findings; all the species delimitation models used consistently identified seven MOTUs for the American continent and an extra G. altavela MOTU restricted to Africa. In addition, our results and models exceeded the worldwide accepted interspecific threshold of 2.0%. Remarkably, our results support the taxonomic reinstatement of Gymnura afuerae (Hildebrand, 1946) as a valid species, with a range expanding into the ETP in the Southern Hemisphere. Similarly, our data support the recent suggestion of resurrecting Gymnura valenciennii (Duméril, 1865) as a valid species in the western Atlantic. These findings urge a reassessment of the conservation status and a comprehensive taxonomic revision of American butterfly rays.

The abundance of shark and actinopterygian fossils in the Cretaceous and Paleogene strata of the Atlantic Coastal Plain is well documented; but much remains unknown about the survivorship patterns of these major components of shallow marine faunas in the western Atlantic through the K/Pg mass extinction. To shed light on this subject, we describe an assemblage of new actinopterygian, chondrichthyan, and reptilian microfossils recently recovered from the Maastrichtian Navesink and Maastrichtian–Danian Hornerstown formations at the Jean and Ric Edelman Fossil Park at Rowan University in Mantua Township, New Jersey. The new microfossils clarify extinction patterns across the K/Pg, create temporal and geographic range extensions for several taxa, and expand the known fauna of this regionally-rare and important K/Pg-boundary locality. We report 11 new additions to the vertebrate fauna of Edelman Fossil Park, the first Paleocene record of Saurocephalus lanciformis, the first Cretaceous records of Paralbula marylandica and Palaeogaleus vincenti, and the first recovery of gar and dercetid fish remains from the Paleocene in New Jersey (the last indicating that these fish survived the K/Pg extinction in the western Atlantic). Geographic range extensions include: Notidanodon brotzeni into the Western Hemisphere, Saurocephalus into northeastern North America and Phyllodus paulkatoi to the eastern coast of North America. A dentary of a juvenile alligatorid, Bottosaurus harlani, indicate that the mandible exhibited isometric growth through ontogeny. Our findings generally agree with other studies that these groups were significantly impacted by the extinction event, that extinctions were selective, and recovery was slow. This wealth of novel insights garnered from microfossils in this study highlights their critical importance for elaborating past faunas and illuminating the character of ancient ecosystems. We therefore recommend microsieving as a fruitful method for future faunal studies of shallow-marine strata and predict that such efforts will frequently yield similar important insights.

The mysterious scarcity of ‘fish’ in an extensive epicontinental sea has always intrigued countless researchers who worked with the South American Devonian, especially in the Malvinoxhosan (= Malvinokaffric) Paraná Basin. This scarcity is probably related to taphonomic factors and/or lack of experience of collectors with fossil ‘fish’. Currently, the vertebrate record of the Devonian of the Paraná Basin is restricted to three chondrichthyan fin fragments and an actinopterygian mandible. Here we describe the first ‘fish’ fossils from the northwest edge of the Paraná Basin, represented by Chondrichthyan fin spine, scales, and teeth, consisting in the oldest Devonian ‘fish’ in the basin, attributed to the Pragian-Emsian of Mato Grosso do Sul state. The morphology of the fin-spine is consistent with a stem chondrichthyan morphotype, and the teeth bear resemblance in cusp morphology to those of the protacrodontid type. Despite the low taxonomic refinement, this new record in the Devonian of the Paraná Basin shows the presence of ‘fish’ throughout the Basin already in the late Pragian – early Emsian. This is relevant, because the Paraná Basin is an important region for better understanding the distribution of the South American Devonian vertebrate fauna through time and space. [ABSTRACT FROM AUTHOR]

To smell, fish rely on passive water flow into their olfactory chambers and through their olfactory rosettes to detect chemical signals in their aquatic environment. The olfactory rosette is made up of secondarily folded tissues called olfactory lamellae. The olfactory morphology of cartilaginous fishes varies widely in both rosette gross morphology and lamellar microstructure. Previous research has shown differences in lamellar sensory morphology depending on the position along the rosette in hammerheads (family Sphyrnidae). Here, we investigate if this pattern continues in members of two other chondrichthyan families: Squalidae and Chimaeridae. Using contrast-enhanced microCT and scanning electron microscopy, we investigated patterns in lamellar morphology based on lamellar position along the olfactory rosette in Pacific spiny dogfish (Squalus suckleyi) and spotted ratfish (Hydrolagus colliei). We describe the gross olfactory rosette anatomy and lamellar microstructure of both species. We also put forth a new method, combining 3D morphological microCT data with 2D SEM microstructure data to better approximate lamellar sensory surface area. We found that in both species, lamellae in the center of the rosette were larger with more secondary folds. However, we found no significant differences in lamellar sensory surface area among lamellar positions. Previously, differences in lamellar sensory morphology have been tied to the internal fluid dynamics of the olfactory chamber. It is possible that the internal flow dynamics of these species are like other chondrichthyan models, where water flow patterns differ in the lateral vs the medial part of the organ, and the consistent distribution of sensory tissue does not correspond to this flow. Alternatively, the olfactory morphology of these species may result in uniform flow patterns throughout the olfactory chamber, correlating with the consistent distribution of sensory tissue throughout the organ. This study emphasizes that further investigations into chondrichthyan fluid dynamics is paramount to any future studies on the correlations between distribution of sensory tissues and water flow. [ABSTRACT FROM AUTHOR]

Despite the high diversity of elasmobranch fishes in the Balearic Islands, knowledge of their biology and population dynamics is still scarce. A recent mark-and-recapture experiment off the Balearic Islands tagged 3738 individuals of 23 shark and batoid species during MEDITS and CANAL bottom trawl scientific surveys from June 2021 to August 2023. Retrieval was reported for the sharks Scyliorhinus canicula and Mustelus mustelus, revealing relatively small home ranges for these species (0.2–38.5 km and 7.8–15.3 km for S. canicula and M. mustelus, respectively). Recapture efficiency was higher from scientific surveys than from commercial catches, highlighting potential challenges in collaboration with fishermen and recapture reports. Density estimates obtained from the MEDITS bottom trawl survey suggest a much larger population for S. canicula than estimates from the mark–recapture data, indicating MEDITS density estimates for this species may be overestimated due to its scavenger behavior perhaps favoring individuals searching for discards aggregated in the fishing grounds. This study emphasizes the importance of monitoring, collaborative efforts, and improved reporting mechanisms to enhance our understanding of elasmobranch populations and provide support for sustainable management of these vulnerable marine species. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Estimating how traits evolved and impacted diversification across the tree of life represents a critical topic in ecology and evolution. Although there has been considerable research in comparative biology, large parts of the tree of life remain underexplored. Sharks are an iconic clade of marine vertebrates, and key components of marine ecosystems since the early Mesozoic. However, few studies have addressed how traits evolved or whether they impacted their extant diversity patterns. Our study aimed to fill this gap by reconstructing the largest time-calibrated species-level phylogeny of sharks and compiling an exhaustive database for ecological (diet, habitat) and biological (reproduction, maximum body length) traits. Using state-of-the-art models of evolution and diversification, we outlined the major character shifts and modes of trait evolution across shark species. We found support for sequential models of trait evolution and estimated a small to medium-sized lecithotrophic and coastal-dwelling most recent common ancestor for extant sharks. However, our exhaustive hidden traits analyses do not support trait-dependent diversification for any examined traits, challenging previous works. This suggests that the role of traits in shaping sharks' diversification dynamics might have been previously overestimated and should motivate future macroevolutionary studies to investigate other drivers of diversification in this clade. [ABSTRACT FROM AUTHOR]

The reproductive diversity of extant cartilaginous fishes (class Chondrichthyes) is extraordinarily broad, reflecting more than 400 million years of evolutionary history. Among their many notable reproductive specialisations are viviparity (live‐bearing reproduction) and matrotrophy (maternal provision of nutrients during gestation). However, attempts to understand the evolution of these traits have yielded highly discrepant conclusions. Here, we compile and analyse the current knowledge on the evolution of reproductive diversity in Chondrichthyes with particular foci on the frequency, phylogenetic distribution, and directionality of evolutionary changes in their modes of reproduction. To characterise the evolutionary transformations, we amassed the largest empirical data set of reproductive parameters to date covering nearly 800 extant species and analysed it via a comprehensive molecular‐based phylogeny. Our phylogenetic reconstructions indicated that the ancestral pattern for Chondrichthyes is 'short single oviparity' (as found in extant holocephalans) in which females lay successive clutches (broods) of one or two eggs. Viviparity has originated at least 12 times, with 10 origins among sharks, one in batoids, and (based on published evidence) another potential origin in a fossil holocephalan. Substantial matrotrophy has evolved at least six times, including one origin of placentotrophy, three separate origins of oophagy (egg ingestion), and two origins of histotrophy (uptake of uterine secretions). In two clades, placentation was replaced by histotrophy. Unlike past reconstructions, our analysis reveals no evidence that viviparity has ever reverted to oviparity in this group. Both viviparity and matrotrophy have arisen by a variety of evolutionary sequences. In addition, the ancestral pattern of oviparity has given rise to three distinct egg‐laying patterns that increased clutch (brood) size and/or involved deposition of eggs at advanced stages of development. Geologically, the ancestral oviparous pattern arose in the Paleozoic. Most origins of viviparity and matrotrophy date to the Mesozoic, while a few that are represented at low taxonomic levels are of Cenozoic origin. Coupled with other recent work, this review points the way towards an emerging consensus on reproductive evolution in chondrichthyans while offering a basis for future functional and evolutionary analyses. This review also contributes to conservation efforts by highlighting taxa whose reproductive specialisations reflect distinctive evolutionary trajectories and that deserve special protection and further investigation. [ABSTRACT FROM AUTHOR]

This article discusses the observation of the critically endangered soupfin shark in the Changing Salish Sea. The study confirms the presence of soupfin sharks in Hammersley Inlet through fishing efforts and sampling. The findings suggest that the presence of soupfin sharks may have implications for trophic dynamics and fisheries management in the region. The article also provides a list of references for further research on marine ecosystems in the Salish Sea and surrounding areas. [Extracted from the article]

Female sperm storage (FSS) has been reported in Chondrichthyans species, and involves the prolonged maintenance of viable sperm after mating events, prior to egg fertilization. Along with multiple paternity (MP–female producing offspring of multiple males within the same litter), FSS has been hypothesized to be related to the increased reproductive fitness of cartilaginous fish lineages. The present study aimed to investigate if: (1) are FSS and MP evolutionarily related and share the same evolutionary history in Chondrichthyes? (2) How is the presence of FSS implied by extinction and speciation rates and thus related to the current species diversity of the group? To answer these questions, we obtained FSS and MP records for Chondrichthyes species from the literature and performed ancestral reconstruction analyses for each character in the phylogenetic tree. We employed MEDUSA and MiSSE to determine if the shifts in diversification rates were related to the characters along the phylogeny. Finally, we utilized HiSSE to calculate the net diversity rates for observed and unobserved states. The ancestral reconstruction indicates that both characters are plesiomorphic for the group; FSS is suggested to be absent in Lamniformes and Rhinopristiformes, whereas MP may be absent in Galeocerdo cuvier. MEDUSA and MiSSE revealed that all clades lacking FSS showed no increase in rates, while there was a higher diversification rates in clades with FSS. HiSSE identified lower net diversity rates in clades lacking FSS associated with hidden states. Therefore, FSS absence seems to contribute to increased extinction rates by reducing diversity among the Chondrichthyes. [ABSTRACT FROM AUTHOR]

Marine chondrichthyans are experiencing a global decline, but identifying appropriate conservation actions is challenging due to the lack of basic biological information, such as growth parameters and reproduction. In this study, we identify biological and ecological attributes that can be both easily obtainable and are effective predictors of extinction threat.A bioecological attribute database was constructed for marine chondrichthyan species, including information on maximum length, habitat, reproductive mode, trophic level and conservation status, among others. Data sources included the Shark‐References, IUCN and FishBase databases. Following this, a generalized linear model was built with conservation status as the response variable and bioecological attributes as explanatory variables, and the model's accuracy was tested for each group. Then, the model was applied to species not yet classified (data deficient [DD] or not evaluated [NE]) to determine their probability of extinction risk.In total, data were compiled for 1225 species of marine Chondrichthyes (537 sharks, 636 rays and 52 chimaeras); approximately 20% of these species are classified as DD or NE. The model demonstrated high accuracy overall: 95% for chimaeras, 77% for rays and 72% for sharks. Our analysis indicates that, among the species that are classified as DD or NE, 58% of rays, 44% of sharks and 66% of chimaeras may be at risk of extinction.These results clearly demonstrate how bioecological attributes can serve as proxies of extinction risk in Chondrichthyes and provide a solid foundation for conservation planning and prioritization for this ecologically important yet data poor taxon. [ABSTRACT FROM AUTHOR]

Dental microwear analysis is a well-established technique that provides valuable information about the diets of extant and extinct taxa. It has been used effectively in most major groups of vertebrates. However, in chondrichthyans, these methods have been implemented only recently in the form of dental microwear texture analysis, with conflicting results. Causes intrinsic to chondrichthyan biology, such as limited food-to-tooth contact, low diversity in terms of trophic categories or fast tooth replacement, have been suggested to reduce diet-related wear on individual teeth, hindering the use of this approach for reliable dietary reconstruction. Here, we explored the relationship between diet and dental microwear in chondrichthyans by using 2D analysis, which can provide finer-scale identification and accurate definition of scratch morphology from tooth surfaces a priori. Scratches were counted and measured on the teeth of 34 extant elasmobranchs grouped into three categories (piscivorous, durophagous and generalist) according to dietary preferences. Our results revealed specific patterns of tooth microwear as a function of dietary abrasiveness, enabling the discrimination of trophic groups and thus establishing a useful comparative framework for inferring aspects of trophic ecology in fossils. We then used this information to study dental microwear in six fossil species from the same locality and stratigraphic levels. First, analyses of the enameloid surfaces of the fossil show that post-mortem alterations are distinguishable, allowing reliable quantification of diet-related ante-mortem microwear signatures. Discriminant analysis allowed the recognition of microwear patterns comparable to those of living sharks and linked them to specific trophic groups with high probability levels (> 90%). Thus, microwear features developing on chondrichthyan teeth during feeding are intense enough to retain information regarding diet preferences. 2D microwear analysis can track this information, proving to be a useful tool for providing significant information not only about diet but also about oral processing mechanisms in extinct chondrichthyans. [ABSTRACT FROM AUTHOR]

Parthenogenesis, or virgin birth, describes a mode of reproduction where an egg develops into an offspring without fertilization, and is observed across various vertebrate taxa, excluding mammals. Obligate parthenogenesis, found in around 100 vertebrate species and 1000 invertebrate species, is relatively rare. Conversely, facultative parthenogenesis, where females can reproduce both sexually and parthenogenetically, is observed in some vertebrates, including elasmobranchs. Notably, this phenomenon in elasmobranchs is mainly documented in captivity, allowing for detailed long-term observation. Specifically, this study reports the first case of facultative parthenogenesis in the common smooth-hound shark Mustelus mustelus, a species classified by IUCN as endangered. Here we show that the juvenile M. mustelus were born through parthenogenesis, exhibiting homozygosity at each genetic marker, consistent with terminal fusion automixis. Remarkably, this finding reveals that parthenogenesis can occur annually in these sharks, alternating between two females, and conclusively excludes long-term sperm storage as a cause. Consequently, this enhances our understanding of parthenogenesis in elasmobranchs and highlights the reproductive flexibility of M. mustelus. Overall, these results contribute to our broader understanding of reproductive strategies in elasmobranchs, which could inform conservation efforts for endangered species. [ABSTRACT FROM AUTHOR]

Hybodontiformes are considered the closest relatives of modern sharks and were the dominant shark group throughout most of the Mesozoic. Although, originally a marine group, during their long temporal range, they conquered the freshwater environment. This is the case of numerous taxa known in northern Gondwana. Here, we report the presence of the hybodontiform Aegyptobatus in the Albian-Cenomanian Alcântara Formation of the São Luis Basin, Northeastern Brazil. A comparison made with other hybodontiform teeth from the Northern Gondwana suggests that the teeth from the Alcântara Formation is noticeably the same species found in the late Cenomanian Bahariya Formation of Egypt, A. kuehnei. Although probably restricted to freshwater, the new discovery increases the geographic range of this taxon, adds one more common taxon between the Brazilian Alcântara Formation and Cretaceous units of North Africa, and extends the temporal range of this taxon down into the Albian-Cenomanian. [ABSTRACT FROM AUTHOR]

Ultrasound imaging can be used as an effective tool to measure the reproductive status and condition of sharks. This usually requires restraint of the subject, which is not feasible in the wild when the target species is of conservation concern and very large, as is the case for whale sharks. Our study invoked a behavioral response in free-swimming whale sharks that allowed snorkelers to image internal organs and structures using a submersible ultrasound scanner linked to an iPhone in an underwater housing. We were able to reliably locate and monitor the heart and other internal organs inside the body cavity, structures inside the head, and image skin and muscle in the dorsal surface of the sharks. The technique is evaluated as a means for assessing the condition and reproductive status of free-swimming whale sharks. [ABSTRACT FROM AUTHOR]

The article discusses a study that validates a new method for monitoring hormone levels in sharks. The researchers analyzed testosterone levels in the skin of sharks that were caught unintentionally as bycatch. The study found that skin biopsies can be a non-lethal and minimally invasive technique for evaluating the endocrine mechanisms in sharks. The research provides insights into the reproductive cycles and breeding success of sharks and could have implications for conservation programs. [Extracted from the article]

AbstractReproduction is a fundamental biological process for producing offspring and ensuring the continuation of the species. With nearly 35,000 fish species worldwide exhibiting a very diverse range of reproductive systems and strategies, the study of fish reproduction is a significant challenge. Research into various fish reproductive models is driven by their use in human biomedical applications, improving the diversification and sustainability of aquaculture species, and developing strategies for biodiversity conservation. These models must be approached from an animal ethics perspective, considering the welfare of the species under study and applying the 3Rs principle (Replacement, Reduction and Refinement). This principle focusses on replacing animals with alternative methods wherever possible, reducing the number of animals used and refining procedures to minimize suffering. While destructive sampling of wild aquatic species should be minimized, the need remains to provide information on reproduction as an important parameter for delineating management and conservation programs. One of the practices that helps reduce and replace the use of animal testing is the scientific study of individuals obtained through bycatch. This is the case for some chondrichthyans, and endangered fish species included in conservation programs. Regarding fish species that are kept under human care (commonly called captivity), studies on reproduction are essential to improve well-being and increase production of farmed species. Research on fish reproduction requires expanding basic knowledge of broodstock management tools, such as gamete quality assessment, reproductive behavior studies, the use of hormone therapies to stimulate reproduction, and the development of non-lethal or less invasive methods using body fluids (e.g., mucus, seminal plasma, blood plasma, or urine) to study reproductive status, as well as novel markers from state-of-the-art omics research. This review describes a multidisciplinary approach that includes the aforementioned reproductive management tools, indicators of welfare, and next-generation sequencing techniques using samples collected by minimally invasive methods. [ABSTRACT FROM AUTHOR]

Composition, size distribution, structure, and function of deep‐sea marine communities must be understood before they are impacted by anthropogenic effects. The deep‐sea ecosystem of the Colombian Caribbean Sea is unexploited with no fishing activity ever registered. We quantified the current state of the marine community using body size distribution (size‐spectra), size‐based indicators, minimum length (LMIN), maximum length (LMAX), average length (Lmean), standard deviation of length (LSD), 10th and 90th percentiles of the length distribution, Shannon–Wiener diversity (H′), and Pielou's evenness (J′) to generate a baseline of potential ecological indicators that contribute to management and conservation of the Colombian bento‐demersal community of deep‐sea marine ecosystem. Sampling was in the Colombian Caribbean Sea at 58 stations during four samplings in August and December 2009, 21 stations in March and May 2010, and 45 stations from August to December 2020, using the swept area method, at depths of 200–550 m. Catches included >50% families and species of fish, followed by 27 families (30%) and 33 and species (37%) of crustaceans. Chondrichthyes included 14% families and 9–11% species. Cephalopods included 2–3% families and 1–4% species. Size‐spectra analysis confirmed expected values for unexploited communities in three sampling years for teleostei, crustacea, and whole community. [ABSTRACT FROM AUTHOR]

Acoustic telemetry has been used to monitor the movement of aquatic animals in a broad range of aquatic environments. Despite their importance, mangrove habitats are understudied for the spatial ecology of elasmobranchs, with acoustic telemetry rarely used inside mangrove habitats. One reason for this may be a general assumption that acoustic signals would not be able to be detected by receivers in such shallow, structurally complex, environments. This study tested whether acoustic receivers can be used inside mangrove habitats to track the movement of sharks and rays. Thirty‐eight receivers were deployed in a mangrove system in Pioneer Bay, Orpheus Island, Great Barrier Reef, including inside mangroves, mangrove edges, and adjacent reef flat areas. The detection range and receiver performance metrics, such as code detection efficiency, rejection coefficient, and noise quotient, were examined and tested among habitats. The results highlighted that the signal from transmitters was successfully detected inside mangrove habitats as well as on the adjacent reef flat. The range to detect at least 50% of transmissions was up to 20 m inside mangroves and up to 120 m outside mangroves. The performance metrics of acoustic receivers inside the mangrove habitat were characterized by low background noise, low rejection rates, and reasonably high code detection efficiency. Furthermore, this study tested the application of this method on juvenile blacktip reef shark Carcharhinus melanopterus and mangrove whipray Urogymnus granulatus, and demonstrated that it can be used to successfully track animals inside mangrove habitat. This novel method could reveal further information on how sharks and rays use mangrove habitats. [ABSTRACT FROM AUTHOR]

The Turkish marine fish diversity was revised and updated in this study based on data published in the last decade. There are currently 552 species in the inventory, reflecting an increase of 7.8% since the previous checklist and belonging to the classes of Teleostei (479 spp.), Elasmobranchii (68 spp.), Chondrostei (3 spp.), Petromyzonti (1 sp.), and Holocephali (1 sp.). Twelve species were excluded from the faunal list due to the lack of valid proof of their presence, the distribution ranges of an additional 12 species were corrected, two new records (Istiompax indica (Cuvier, 1832) and Mola alexandrini (Ranzani, 1839)) previously unknown from Türkiye were presented for the first time, and a range expansion report for Parophidion vassali (Risso, 1810) was given. In terms of number of species, the Levantine Sea coast of Türkiye had the highest diversity with 477 species, followed by the Aegean Sea (466 spp.), Sea of Marmara (277 spp.), and Black Sea (162 spp.). Alien fishes reported from the region have now reached 90 species, corresponding to 16.3% of the total ichthyofauna, the majority of which occur along the Levantine coast with significantly decreasing numbers in the clockwise direction towards the Black Sea. [ABSTRACT FROM AUTHOR]

Remoras are a highly specialised group of fishes known to associate with a range of marine megafauna, including elasmobranchs, cetaceans and marine reptiles. Remoras appear to benefit from these interspecific interactions through consumption of host dermal parasites or reduced cost of transport. Shark‐remora associations are widely documented, yet our understanding of the costs and benefits involved in these interactions is poor. Studies frequently make claims about mutualistic, commensalistic or parasitic relationships without providing the necessary quantitative information necessary to make these claims. Here I explain why this approach is problematic, and proceed to examine shark‐remora interactions in a rigorous eco‐evolutionary framework. These interactions cannot be properly classified without considering net evolutionary fitness and context dependence. In reality, shark‐remora interactions are best defined by a multidimensional spectrum of fitness consequences, with net fitness outcomes shifting between mutualism and parasitism (and vice versa) through space and time. [ABSTRACT FROM AUTHOR]

We described fossil teeth assigned to the orectolobiform shark genus, Cederstroemia collected from the tuffaceous sandstone of the Kashima Formation (Santonian) in the Oyubari area, Hokkaido, Japan. This is the first report of fossil remains of Cederstroemia from Asia. Due to the small number of specimens and their poor preservation, we left the studied material in open nomenclature as Cederstroemia sp. At the same time, the studied material may belong to a new previously undescribed morphology of Cederstroemia. The occurrence of Cederstroemia fossils in Japan indicates that this genus dispersed to the northwestern part of the Pacific Ocean in the Late Cretaceous, which considerably extends the range and previously known habitat of this genus. [ABSTRACT FROM AUTHOR]