Search Results (52)

In the Chondrichthyes Raja asterias and Myliobatis aquila and in the Teleost Sparus aurata, the appendicular skeleton of the pectoral fins (including the calcified structures of the mouth in M. aquila) was investigated to find out how the specific skeletal segments were formed and stiffened over the course of evolution, not only with regard to the adaptation of the ontogenesis of the cartilage “anlagen” to the mechanical requirements of locomotion in the water column, but also to the specific feeding habits (durophagy) of M. aquila. The morphology of the pectoral fins of the three species showed a different layout, characterized by the geometry of the basic units (aligned tesserae and calcified radial columns), which provide varied flexibility of the pectoral fins, suggesting an adaptation to the “pelagic” and “benthic” locomotion patterns in the environment where the species live. The morphology of the calcified structures in the mouth of M. aquila showed the presence of two different masticatory systems: the first (external) with the rows of teeth resting on the maxillary and mandibular arches, and the second (internal, in the oral cavity) with the symphyseal plates specialized for durophagy. Chemical–physical analyses revealed that the calcified cartilage matrix of the Chondrichthyes fin rays, teeth and durophagy plates is stiffened by the same Ca₃(PO₄)₂ mineral phase deposed in the organic matrix of the Teleost S. aurata fins (with the characteristic SEM morphological texture of calcified bone matrix). The hitherto unknown presence of two different chewing systems in M. aquila documents an evolutionary adaptation to nutritional requirements that can be explained by two hypotheses: the coexistence of two functioning systems in current specimens, allowing for the ingestion of harder and softer prey (or plant food), or the persistence of a rudimentary dentition that is no longer used (vestigial dentition). Furthermore, the texture of the calcified matrix in teleost fishes, as observed by scanning electron microscopy, may indicate a bone-like organic matrix substrate, similar to that found in endochondral ossification. Full article

The Indian Ocean is globally significant in terms of capture fisheries, and understanding the species composition of fish in the Indian Ocean is of great importance for the protection and development of its fishery resources. While coastal fish communities in the Indian Ocean are relatively well-documented, studies on pelagic zones remain sparse, especially for non-target species constituting fishery bycatch. Traditional biodiversity surveys rely on labor-intensive, inefficient trawling methods. To address these limitations, this study aims to apply environmental DNA (eDNA) metabarcoding for a species diversity survey in the Western Indian Ocean, offering a more reliable, efficient, and non-invasive alternative to traditional methods. The results will provide important insights into the region’s fish biodiversity, supporting sustainable management and conservation of fisheries resources in the area. Samples were collected from 130 stations in different water layers in the Western Indian Ocean, and species diversity was analyzed through 12S rRNA gene amplicon sequencing. The results showed that 98 fish species were detected from 176 seawater eDNA samples, belonging to two classes (Actinopteri and Chondrichthyes), 20 orders, 35 families, and 60 genera. Within a depth range of 300 m, there were no significant differences in species diversity parameters among samples from different depths. The orders with the highest relative abundance detected include Scombriformes, Aulopiformes, and Myctophiformes. The species with the highest relative abundance include Thunnus albacares, Alepisaurus ferox, Xiphias gladius, Diaphus fragilis, Decapterus macarellus, Thunnus maccoyii, and Platycephalus cultellatus. The species composition and relative abundance of economic species observed in this study showed, as expected, differences from fishery catch statistics. These results suggest that eDNA technology can not only monitor marine fish diversity more efficiently but also complement the lack of fisheries data. Integrating eDNA technology into routine monitoring in the Western Indian Ocean in the future could promote sustainable management of fisheries resources in the region. Full article

The skate fauna in the Southwest Atlantic Ocean (SWA; 34–55° S) is represented by ~32 species, many of which share external features that have led to misidentifications and deficient fishery statistics. The use of DNA barcoding to discriminate SWA skate species was explored after 20 years of surveys. COI sequences were subjected to distance-based neighbor-joining (NJ), maximum likelihood (ML), barcode index number (BIN), automatic barcode gap discovery (ABGD), and nucleotide diagnostic character (NDC) analyses. For widely distributed species, a haplotype network was built. Overall, 187 specimens and 31 egg cases from 26 skate species were barcoded. NJ and ML analyses showed that nearly all species exhibited unique barcodes or clusters of closely related haplotypes, except for Psammobatis normani/P. rudis and Dipturus trachyderma/D. argentinensis. The first pair was discriminated by NCD. BIN analysis recovered 17 groups, whereas ABGD recovered 23, better reflecting taxonomic diversity. In summary, 24 species were resolved by COI. Phylogeographic signals were observed for Amblyraja doellojuradoi and Zearaja brevicaudata. Compiling our results with data from BOLD, almost all the species occurring in the area possess barcodes, contributing to completing and curating the BOLD reference library, which constitutes an important tool for resolving taxonomic issues, tracing fishery products, and performing eDNA biomonitoring. Full article

Elasmobranchs (Chondrichthyes, Elasmobranchii) are exposed to a variety of gastrointestinal parasites acquired through the ingestion of infected prey. An increasing amount of evidence suggests the usefulness of parasitological information to elucidate aspects of the biology and ecology of sharks and rays, to inform the correct management and conservation of their stocks and the appropriate husbandry of captive specimens. This study aims to identify at the morphological and molecular level the helminth parasites found in the stomachs and intestines of various elasmobranchs accidentally caught by Mediterranean fisheries, with the aim of updating and providing new information on the parasitic fauna of these species. Specimens of smooth-hound Mustelus mustelus, blackspotted smooth-hound Mustelus punctulatus, blue shark Prionace glauca, spiny dogfish Squalus acanthias, lesser-spotted dogfish Scyliorhinus canicula, pelagic stingray Pteroplatytrygon violacea and Mediterranean starry ray Raja asterias were examined. The parasitological examination allowed us to identify the nematode Acanthocheilus rotundatus in the two species of smooth-hounds analyzed, the tapeworm species Scyphophyllidium exiguum, S. prionacis, Anthobothrium caseyi and Nybelinia indica in P. glauca, the nematodes Hysterothylacium aduncum and Proleptus obtusus in S. acanthias and S. canicula, respectively, and finally the nematode Pseudanisakis rajae and the tapeworm Nybelinia sp. in Raja asterias. Some observations represent new reports at a geographical level, in particular, those on A. caseyi in P. glauca and H. aduncum in S. acanthias from the Adriatic Sea, or first host records, such as S. exiguum and N. indica in P. glauca or P. rajae. in R. asterias. The results of this survey represent a contribution to broadening the knowledge of the parasitic fauna of these elasmobranchs in the Mediterranean Sea. From more in-depth future studies, it will be possible to reach more solid evidence and general conclusions on aspects relating to the biology, ecology, and health of the investigated species, offering useful information for their conservation and management. Full article

The presence of the white shark (Carcharodon carcharias) in the Mediterranean Sea is well documented, but mainly through historical and opportunistic records. Historically, the Adriatic Sea, particularly its eastern coastline, was considered a hotspot for white sharks, with relatively frequent reports of juvenile specimens suggesting a potential nursery area. However, since the second half of the 20th century, the abundance of white sharks in the Adriatic has experienced a dramatic decline, with the last confirmed sighting recorded in 2011. In this study, we report the recent capture of a young-of-the-year (YOY) white shark off the Croatian coast, previously misidentified as a porbeagle shark (Lamna nasus). In addition, we revisit historical records of white sharks in the Adriatic Sea to assess whether this region can be considered a nursery area. Our findings highlight significant gaps in the understanding of white shark spatial ecology and reproductive biology in the Mediterranean Sea. Furthermore, this study emphasizes the critical role citizen science and public engagement can play in documenting occurrences of these elusive and endangered predators, offering valuable insights for future conservation efforts. Full article

The Alboran Sea is the westernmost sub-basin of the Mediterranean Sea, and it is connected to the Atlantic Ocean through the Strait of Gibraltar. The Alboran Ridge is located in the middle of the Alboran Sea and represents a hotspot of biodiversity in the Mediterranean Sea. Besides their critical importance, there are few studies on the communities and changes in biodiversity, and they mostly concentrate on infralittoral and circalittoral bottoms. In this work, the composition, structure and bathymetric and temporal changes of megafauna of the Alboran Ridge were examined. Samples were collected from MEDITS surveys carried out between 2012 and 2022 at depths ranging from 100 to 800 m. Analyses were performed separately for each of the taxonomic groups: osteichthyes, chondrichthyes, crustaceans, molluscs, echinoderms and “other groups”. There was no common spatial organization for each of the faunistic groups studied, although most of them displayed differences between the shelf and the slope. The continental shelf was characterized by the highest values of community metrics such as abundance, biomass, species richness and mean weight of species for all groups except for chondrichthyes and crustaceans. Decreasing trends of some community metrics were detected in some of the faunistic groups throughout the study period. Full article

In order to collect information on ichthyofauna of a deep-sea vulnerable marine ecosystem (VME) network along the Apulian margin (central Mediterranean Sea), two low-impact sampling tools were used in three VMEs characterized by cold-water corals (CWC), namely Bari Canyon (BC), off Monopoli (Mn), and off Santa Maria di Leuca (SML). Using an experimental longline, 53 deployments were carried out between a 314 and 650 m depth for a total of 217 fishing hours, whereas when using the baited lander MEMO (Marine Environment MOnitoring system), 31 deployments were carried out between 427 and 792 m, for a total of 223 h of video recordings. A total of 37 taxa were recorded, comprising 13 Chondrichthyes and 24 Osteichthyes. The similarities in species observed among the VMEs confirm the presence of a network of CWC-VMEs along the Apulian margin, whereas some differences detected are due to the different abundance of some species, such as Galeus melastomus, Helicolenus dactylopterus, and Phycis blennoides. The presence of commercial species, vulnerable/endangered cartilaginous fishes, and large and sexually mature individuals of G. melastomus, H. dactylopterus, and Pagellus bogaraveo in all the VMEs confirms that the network of CWC-VMEs along the Apulian margin can act as a network of refuge areas and an essential fish habitat (EFH) for species threatened by fishing activities. Full article

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. Full article

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. Full article

The mammalian complement system constitutes a highly sophisticated body defense machinery. The evolutionary origin of the complement system can be traced to Coelenterata as the presence of the central component C3 and two activation proteases BF and MASP. In the present study, the main complement components were screened and analyzed from the genomes of different species in metazoan subphyla/phyla. C1q with classical domains can be traced to Annelida, and ficolin and MBL to Urochordata. C1r and C1s are only found in Chondrichthyes and even higher species, and MASP is traced to Coelenterata. In the evolutionary tree, C1r from Vertebrates is close to MASP1/2/3 from Deuterostomia and Coelenterata, and C1s from Vertebrates is close to MASP-like protease (MASPL) from Arthropoda, Mollusca, and Annelida. C2, BF, and DF can be traced to Mollusca, Coelenterata, and Porifera, respectively. There are no clear C2 and BF branches in the evolutionary tree. C3 can be traced to Coelenterata, and C4 and C5 are only in Chondrichthyes and even higher species. There are three clear C3, C4, and C5 branches in the evolutionary tree. C6-like (C6L) and C8 can be traced to Urochordata, and C7-like (C7L) can be traced to Cephalochordara. C6L, C7L, and C8 from Urochordata and Cephalochordara provide the structural conditions for the formation of Vertebrate MAC components. The findings unveil the evolutionary principles of the complement system and provide insight into its sophistication. Full article

A remarkable new deep-water skate, Leucoraja longirostris n. sp., is described based on eight specimens caught during different expeditions to the southern Madagascar Ridge in the southwestern Indian Ocean. The new species differs from all congeners by its remarkably long and acutely angled snout (horizontal preorbital length 17.2–22.6% TL vs. 8.5–11.9% TL and 4.2–6.1 vs. 1.7–3.5 times orbit length, snout angle 65–85° vs. 90–150°). Furthermore, it is apparently endemic to the Madagascar Ridge, distant from the known distribution areas of all congeners. In addition to L. fullonica and L. pristispina, L. longirostris n. sp. is also the only species with plain dorsal coloration. Furthermore, the new species is the only Leucoraja species with an external clasper component dike and, besides L. wallacei, the only one with four dorsal terminal (dt) cartilages. The shape of the accessory terminal 1 (at1) cartilage with four tips is also unique within the genus. A new approach for the visualization of the clasper characters is introduced based on 3D models of all skeletal and external features. This enables a much easier and much more precise interpretation of every single clasper component, of the entire structure, and, in particular, the relationship between external features and skeletal cartilages. A new English translation of the first diagnosis of Leucoraja is provided, along with a revised generic diagnosis and a key to the species of Leucoraja in the Indian Ocean. Full article

The Amazon region has the largest diversity of freshwater stingrays; however, there are still places where information about this group is scarce. The present work aims to record the occurrence of freshwater stingrays in the Uatumã river basin, Amazonas, Brazil. For this, collections were carried out in three municipalities bathed by the Uatumã River, Presidente Figueiredo, Itapiranga, and São Sebastião do Uatumã. The rays were collected through fishing using a hand net and, after capture, were identified through the pattern of the dorsal and ventral color of the disc, the absence or presence of the labial groove, and the organization of the row of spines on the tail, and were also measured, weighed, and sexed. In total, 69 specimens of Potamotrygonines were captured, 59 of which were from the genus Potamotrygon and ten individuals from the genus Paratrygon. The present study provides preliminary information on the characteristics of freshwater stingray species that may occur in the Uatumã River. Furthermore, new research is necessary to improve the identification of specimens to determine the diversity and elucidate aspects related to the biology of elasmobranchs in the Uatumã River Basin, Brazil. Full article

As long-living apex predators, sharks tend to bioaccumulate trace metals through their diet. The distribution of Al, As, Cd, Co, Cr, Cs, Cu, Fe, Mn, Ni, Pb, V, Zn and Hg in different tissues (muscle, liver, heart, gills and gonads) of large-size (58–390 cm) sharks, some of which rare, of the eastern Mediterranean Sea was studied. Trace metals analyses in samples originating from ten different Chondrichthyes species were performed by inductively coupled plasma–mass spectrometry (ICP-MS) and Cold Vapor Atomic Absorption Spectrometry (CVAAS) for Hg. Data on trace metal levels are for the first time reported herewith for the species O. ferox and H. nakamurai. Higher median concentrations of trace metals were generally determined in the liver. The concentrations of Hg, Cs and As in the muscle increased proportionally with body length. Statistically significant differences between sexes were recorded for Hg, Cr, Ni and As (p = 0.015) in the muscle tissues of P. glauca. Muscle tissue Hg concentrations exceeded the EU maximum limit (1 μg g⁻¹ wet weight) in 67% of the individuals sampled, with the highest concentrations detected in O. ferox and S. zygaena, whereas regarding Pb (limit 0.30 μg g⁻¹ ww), the corresponding percentage was 15%. Arsenic concentrations were also of concern in almost all shark tissues examined. Full article

Members of the genus Brevitrygon are small, locally abundant tropical stingrays (family Dasyatidae) occurring in soft sedimentary habitats of inner continental shelves of the Indo-West Pacific from the Red Sea to Indonesia. Formerly members of the genus Himantura, whose members lack dorsal and ventral skin folds on the tail (typical of most dasyatid genera), folds are present or rudimentary in some Brevitrygon. Important to artisanal fisheries and known to consist of at least five species, these fishes are possibly the most frequently misidentified of all stingrays. Most were inadequately described in the 19th century, and they are often taxonomically confused due to morphological similarity, ontogenetic variability, and sexual dimorphism. Their nomenclatural history is complex with four of the known species represented within the type series of one species, B. walga (Müller & Henle). Also, the type of the species with which B. walga is most often confused, B. imbricata (Bloch & Schneider) from off southern India and Sri Lanka, is in very poor condition. A lectotype has been designated for B. walga (confined to the Bay of Bengal). The genus also contains B. heterura (Bleeker) from the Indo-Malay Archipelago, B. javaensis (Last & White) from off southern Indonesia, and a new species, B. manjajiae sp. nov., from the western Indian Ocean. The former species are redescribed and redefined based largely on a combination of morphometrics, tail morphology, squamation, and molecular data. Molecular divergences were detected within lineages of B. heterura, B. walga and B. manjajiae sp. nov., requiring further investigation. Full article

(1) Background: Labial cartilages (LCs), as their name suggests, lie in the folds of the connective tissue, the lips, framing the gape of elasmobranch chondrichthyans. As such, these cartilages lie laterally to the jaws and marginal teeth. They are considered to influence the ability of creating suction during the feeding process. As past studies have shown, LCs in sharks are as diverse as their varied feeding techniques and differ between species in number, size, shape, and position. This allows establishing parameters for inferring the feeding and hunting behaviors in these ecologically important fishes. (2) Methods: We present a study of LCs based on the CT scans of more than 100 extant shark species and, therefore, represent at least one member of every living family within the Euselachii, excluding batoids. (3) Results: Accordingly, sharks without labial cartilages or that have only small remnants are ram feeders or use pure biting and mainly occupy higher trophic levels (tertiary and quaternary consumers), whereas suction-feeding sharks have higher numbers (up to five pairs) of well-developed LCs and occupy slightly lower trophic levels (mainly secondary consumers). Species with unique feeding strategies, like the cookie-cutter shark (Isistius brasiliensis, an ectoparasite), display distinct shapes of LCs, while generalist species, conversely, exhibit a simpler arrangement of LCs. (4) Conclusions: We propose a dichotomous identification key to classify single LCs into different morphotypes and propose combinations of morphotypes that result in suction feeding differing in strength and, therefore, different hunting and feeding strategies. The conclusions of this study allow to infer information about feeding strategies not only in extant less-known sharks but also extinct sharks. Full article