Search Results (4)

Adult neurogenesis in cartilaginous fish remains a relatively unexplored area, particularly in terms of comparative analysis. This process, defined as the ability of specialized stem cells to generate new functional neurons, has gained prominence due to its relevance in neurodegenerative disease research and regenerative medicine. However, there is an ongoing discussion about when and where it first appeared. Evidence of adult neurogenesis in both teleosts and mammals highlights significant differences, such as the number of newly formed cells and the brain regions involved. Investigating additional cartilaginous fish species, which occupy a basal position in vertebrate phylogeny, could provide valuable insights into the ancient origins of this trait and potentially new general knowledge about the adult neurogenesis process. In this study, we combined immunohistochemistry and in situ hybridization to examine neurogenic activity in three brain regions—the telencephalon, mesencephalon, and cerebellum—of two batoid species: Raja asterias and Torpedo ocellata. Immunohistochemical methods were used to identify neurogenic cells by employing markers for cell proliferation (PCNA), mitosis (pH3), glial cells (S100B), and stem cells (Msi1). Additionally, in situ hybridization was performed to detect neural stem cell mRNA for Notch1, Notch3, and Sox2 in the telencephalon and mesencephalon of Raja asterias. 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

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. Full article

The large variation in vertebral shape and calcification observed among elasmobranch species prevents using a single method for enhancing growth bands and reading age. Further, estimating age and growth parameters can be difficult or impractical when samples are incomplete due to the bycatch of a size-selective fishery. Using a single and rapid method, age readings were obtained on the vertebrae of four batoid species, namely 53 individuals of Dasyatis pastinaca, 51 of Raja asterias, 15 of Torpedo marmorata, and 55 specimens of Torpedo torpedo, from the local small-scale trammel net fishery in the coastal waters (5–20 m depth) of the Central Tyrrhenian Sea during 2019–2021. Based on these data, a statistical routine was developed to obtain multiple estimates of age and growth parameters for incomplete samples due to size-selective fishing. The acceptable agreement between and within readers (intra and inter-reader disagreement < 5%) and the rate of increase in vertebral size with body size (differently ranked across species) demonstrated the consistency of the enhancing method. The parameters estimated by the Von Bertalanffy and Gompertz growth models matched the data available in the Mediterranean Sea for the species studied, with D. pastinaca, T. torpedo, and R. asterias showing the lowest (k = 0.05–0.12), intermediate (k = 0.112–0.19), and highest (k = 0.18–0.23) growth rates, respectively, in line with the life history traits of these species. Overall, the method proved effective both in delineating band pairs in vertebrae of different species and in reliably estimating the age and growth parameters of problematic samples due to size-selective fishing. The proposed method supports the collection of comparable demographic data from other areas where similar multi-specific assemblages are bycatch of size-selective fisheries impacting potential nursery areas and other essential habitats for elasmobranchs. Full article