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The catshark genus Holohalaelurus Fowler is currently represented by five species distributed off the southern and eastern parts of the African coast. Very few parasitological records exist for any of these five species, representing a significant knowledge gap. We report the first monogenean species from the bathydemersal species Holohalaelurus regani (Gilchrist): a new species of Microbothriidae Price, 1936, Leptomicrobothrium holohalaelure n. sp. from the dorsal skin surface, and a new species of Hexabothriidae Price, 1942 representing a new genus, Scyliorhinocotyle narvaezae n. gen., n. sp., from the gill lamellae. Both monogenean records represent the first for any member of the catshark genus Holohalaelurus. Previously we focused on the identification of monogenean taxa of emerging veterinary importance for public aquaria. We now begin a focused effort to document a generally unexplored monogenean biodiversity from diverse marine habitats off South Africa.

In this study, we investigated ontogenetic and sexual changes of the brain scaling as well as the scaling and the relative size of six major brain areas in the small-spotted catshark Scyliorhinus canicula from the Mediterranean Sea. The brain somatic index (0.31–1.25%) did not differ significantly between sexes but was significantly affected by size with smaller specimens exhibiting higher values. Brain growth exhibited negative allometry (allometric coefficient 0.634), not affected by sex or maturity status. The brain growth rate was found to be higher compared with a previous study from the Atlantic Ocean. Regarding the scaling of the brain areas, the olfactory bulbs scaled with positive allometry, the telencephalon and the diencephalon scaled with the same rate of negative allometry, the mesencephalon exhibited even higher negative allometry, while the cerebellum and the medulla oblongata both followed a close-to-isometric growth pattern. Immature S. canicula possessed a larger mesencephalon and diencephalon, highlighting the importance of vision in this life period, while mature specimens had enlarged olfactory bulbs, indicating that olfaction may be more important after the animal attains sexual maturity. In respect of sexual dimorphism, males had a larger cerebellum and medulla oblongata, while females had enlarged telencephalon and olfactory bulbs.

Descriptions of egg cases and hatchlings of the Bali catshark Atelomycterus baliensis and the Australian marbled catshark Atelomycterus macleayi are provided. Comparisons are made with two of their congeners, banded sand catshark Atelomycterus fasciatus and coral catshark Atelomycterus marmoratus. The Atelomycterus egg cases have the same general morphology, i.e., elongate with anterior and posterior waists, a depressed and truncate anterior end sometimes with attachment fibres, a medially tapered posterior end with two horns sometimes terminating in short, tightly curled tendrils and four respiratory fissures (one at each left corner on opposing sides). Morphometric measurements taken of the egg cases of the four species differed significantly when subjected to multivariate analysis, with unique characters enabling distinction between them. The morphological characters that best distinguished the Atelomycterus species from each other were anterior border width, posterior waist width and posterior case width. Thus, egg case morphology could be used to distinguish the egg cases of the four Atelomycterus species examined, consistent with other studies on scyliorhinid and pentanchid egg cases. Colouration of A. baliensis and A. macleayi juveniles was similar to that of other Atelomycterus juveniles in being pale with a series of dark-brown distinct dorsal saddles along the body, blotches and sometimes with a low number of small dark spots.

The Izak catshark Holohalaelurus regani and the yellow-spotted catshark Scyliorhinus capensis both occur over the continental shelf around South Africa and are often caught together as bycatch in d...

In shark populations, variation in sexual size dimorphism (SSD) appears to be related with the reproductive mode. Here, we aimed to investigate the reproductive biology of the narrowmouth catshark Schroederichthys bivius, an oviparous shark with size and secondary sexual dimorphism. For this purpose, specimens were collected during research surveys covering almost their entire distribution in the southwestern Atlantic continental shelf. Size distribution ranged from 196 to 810 mm total length (TL) in males and from 258 to 630 mm TL in females, and the mean size at maturity was 563 mm TL for males and 485 mm TL for females. Males appeared to be capable of mating all times of the year, while females could exhibit an annual reproductive cycle. Besides SSD, with males attaining higher maximum TL and size at maturity, spatial sexual segregation appears to be observed in mature specimens. Although differences in size at maturity were observed between surveys, these differences did not show a latitudinal pattern. The spatial overlap observed between closed areas to trawling and the distribution of egg-bearing females suggests that these closed areas, although designed and established to protect other species, may represent an important measure also for the conservation of S. bivius.

Background The onset of morphological differences between related groups can be tracked at early stages during embryological development. This is expressed in functional traits that start with minor variations, but eventually diverge to defined specific morphologies. Several processes during this period, like proliferation, remodelling, and apoptosis for instance, can account for the variability observed between related groups. Morphological divergence through development is often associated with the hourglass model, in which early stages display higher variability and reach a conserved point with reduced variability from which divergence occurs again to the final phenotype. Results Here we explored the patterns of developmental shape changes in the lower jaw of two shark species, the bamboo shark (Chiloscyllium punctatum) and the catshark (Scyliorhinus canicula). These two species present marked differences in their foraging behaviour, which is reflected in their adult jaw morphology. By tracing the developmental sequence of the cartilage condensation, we identified the onset of cartilage for both species at around stage 31. Other structures that developed later without a noticeable anlage were the labial cartilages, which appear at around stage 33. We observed that the lower jaw displays striking differences in shape from the earliest moments, without any overlap in shape through the compared stages. Conclusions The differences observed are also reflected in the functional variation in feeding mechanism between both species. Likewise, the trajectory analysis shows that the main differences are in the magnitude of the shape change through time. Both species follow a unique trajectory, which is explained by the timing between stages.

En la presente investigación se analizó la comunidad de parásitos de dos especies de tiburones del sur de Chile debido al escaso conocimiento de la relación entre parásitos y tiburones de la zona. Un total de 24 especímenes del tiburón linterna Etmopterus granulosus y siete especímenes de la pintarroja del sur Schroederichthys bivius fueron recolectados en el estrecho de Magallanes en enero de 2017 y 2018. Se encontró un total de 87 individuos de parásitos pertenecientes a siete especies de parásitos en E. granulosus y 192 individuos de parásitos de siete especies en S. bivius. La abundancia promedio de parásitos fue mayor en la pintarroja del sur que en el tiburón linterna, con 27,5 ± 25,5 parásitos/hospedero y 3,5 ± 3,3 parásitos/hospedero, respectivamente. Pocos parásitos fueron prevalentes y abundantes; tales como los nematodos Pseudoterranova sp. (41,7% de prevalencia; 1,46 parásitos/pez) y Anisakis sp. (29,2% de prevalencia; 1,21 parásitos/pez) presentes en E. granulosus, y el copépodo Tautochondria sp. (85,7% de prevalencia; 9,14 parásitos/pez) y el nematodo Proleptus niedmanni (71,4% de prevalencia; 14,86 parásitos/pez) presentes en S. bivius. La similitud en la composición de especies parásitas fue baja entre E. granulosus y S. bivius (14,6%), ya que sólo dos especies de parásitos, los anisákidos Pseudoterranova sp. y Anisakis sp., fueron compartidos entre ambos hospederos, a pesar de ser especies simpátricas. Por tanto, la desigual composición de los parásitos entre ambas especies de tiburones podría explicarse por sus historias evolutivas distintas, que implican numerosas diferencias ecológicas entre los hospederos.

A rare specimen of Parmaturus melanobranchus was collected from the South China Sea. The complete mitochondrial genome of the specimen was sequenced using Illumina Hiseq platform and assembled with Geneious and Trinity. The mitogenome is 16,687 bp long with a base composition of 30.4% A, 14.1% G, 23.5% C and 32.1% T, respectively. A total of 37 genes were predicted containing 13 protein-coding genes, 2 ribosomal RNA genes and 22 transfer RNA genes. This is the first complete mitochondrial genome published of this species.

We report the adaptation of RNA tomography, a technique allowing spatially resolved, genome-wide expression profiling, to a species occupying a key phylogenetic position in gnathostomes, the catshark Scyliorhinus canicula. We focused analysis on head explants at an embryonic stage, shortly following neural tube closure and of interest for a number of developmental processes, including early brain patterning, placode specification or the establishment of epithalamic asymmetry. As described in the zebrafish, we have sequenced RNAs extracted from serial sections along transverse, horizontal and sagittal planes, mapped the data onto a gene reference taking advantage of the high continuity genome recently released in the catshark, and projected read counts onto a digital model of the head obtained by confocal microscopy. This results in the generation of a genome-wide 3D atlas, containing expression data for most protein-coding genes in a digital model of the embryonic head. The digital profiles obtained for candidate forebrain regional markers along antero-posterior, dorso-ventral and left-right axes reproduce those obtained by in situ hybridization (ISH), with expected relative organizations. We also use spatial autocorrelation and correlation as measures to analyze these data and show that they provide adequate statistical tools to extract novel expression information from the model. These data and tools allow exhaustive searches of genes exhibiting any predefined expression characteristic, such a restriction to a territory of interest, thus providing a reference for comparative analyses across gnathostomes. This methodology appears best suited to species endowed with large embryo or organ sizes and opens novel perspectives to a wide range of evo-devo model organisms, traditionally counter-selected on size criterion.

Atmospheric CO2 levels have been rising due to an increase in anthropic activities and its implications over marine ecosystems are unprecedented. The present study focused on the effects of ocean acidification (OA) on key hematological parameters of the juvenile small-spotted catsharks (Scyliorhinus canicula). Eggs were reared throughout the entire embryogenesis (~4 months) plus 5 additional months, in two experimental treatments (control: pCO2 ~ 400 μatm; and high CO2 : pCO2 ~ 900 μatm, Δ -0.3 pH units). After blood collection, the following hematological parameters were evaluated: (a) normal blood cells count (erythrocytes, leukocytes, and thrombocytes), (b) presence of erythrocytes with nuclear abnormalities, and (c) erythrocyte nucleus to cytoplasmic ratio. Concomitantly, to determine the cardiac and hematopoietic conditions, the spleen and heart to body ratios were also assessed. The present findings indicate that the measured variables may not be affected by elevated pCO2 in this temperate species, as no significant differences were observed between treatments across all the endpoints tested. Nonetheless, it is worth mentioning a decreasing trend observed in a number of thrombocytes associated with OA, which should foster further investigation, regarding other aspects of their coagulation response. Along with OA, other stressors are expected to impact marine life, such as warming and hypoxia. Thus, future research should aim to investigate the cumulative effect of these stressors on hematological parameters in sharks.

The nematode Mooleptus rabuka is recorded in the digestive tract of catshark Apristurus fedorovi caught at the Imperial Ridge (Pacific Ocean). Important morphological features such as the number of cephalic and caudal papillae, the position of amphids and the shape of the gubernaculum are detailed in this parasite species. According to the phylogenetic analyses based on the 18S ribosomal RNA gene sequences, M. rabuka forms a lineage, Mooleptinae nom. nov., which is close to the gnathostomatid genus Echinocephalus (maximum likelihood analysis), or else forms a polytomy with this genus and the lineages of Anguillicola + Spiroxys and Tanqua + ‘Linstowinema’ sp. (Bayesian inference analysis). Overall, our findings do not support the monophyly of the Gnathostomatidae. We elevate spiroxyines to the family status, Spiroxyidae stat. nov., and temporarily consider the Gnathostomatidae to include the following subfamilies: Ancyracanthinae Yorke & Maplestone, 1926, Gnathostomatinae Railliet, 1895 sensu lato and Mooleptinae nom. nov. The name Mooleptinae nom. nov. is suggested instead of the Metaleptinae Moravec & Nagasawa, 2000, which is based on a preoccupied generic name Metaleptus Machida, Ogawa & Okiyama, 1982.

Although knowledge of the bioactive compounds produced by species inhabiting coastal waters is increasing, little is known about the bioactive potential produced by marine species occupying deeper habitats with high biodiversity and productivity. Here, we investigate about the bioactive potential of molecules produced by species that inhabit the crinoid beds, a poorly known essential fish habitat affected by trawling, wherein large amounts of commercial and noncommercial species are discarded. Based on a trawl survey conducted in 2019, 14% of the 64 species discarded on crinoid beds produce molecules with some type of bioactive potential, including, soft corals (Alcyonium palmatum), tunicates (Ascidia mentula), bony fish, such as horse mackerel (Trachurus trachurus), European hake (Merluccius merluccius), and chondrichthyans, such as small-spotted catshark (Scyliorhinus canicula). In addition, 16% of the discarded species had congeneric species that produce compounds with bioactive potential, indicating that such species might also possess similar types of bioactive molecules. Molecules with antioxidant, antitumour, antihypertensive, and antibacterial properties were the most frequent, which could provide the basis for future research aiming to discover new marine-based drugs and compounds for other human uses. Among all species or genera that produce compounds with bioactive potential, 68% presented medium or high vulnerability to trawling. Results show that the discarded catch contains many species, which produce different bioactive compounds that represent an added-value resource. These results highlight the importance of manage properly crinoid beds, to ensure that species that produce molecules with bioactive potential inhabiting these habitats are protected.

The anterior-posterior (AP) axis in chordates is regulated by a conserved set of genes and signaling pathways, including Hox genes and retinoic acid (RA), which play well-characterized roles in the organization of the chordate body plan. The intermediate mesoderm (IM), which gives rise to all vertebrate kidneys, is an example of a tissue that differentiates sequentially along this axis. Yet, the conservation of the spatiotemporal regulation of the IM across vertebrates remains poorly understood. In this study, we used a comparative developmental approach focusing on non-conventional model organisms, a chondrichthyan (catshark), a cyclostome (lamprey), and a cephalochordate (amphioxus), to assess the involvement of RA in the regulation of chordate and vertebrate pronephros formation. We report that the anterior expression boundary of early pronephric markers (Pax2 and Lim1), positioned at the level of somite 6 in amniotes, is conserved in the catshark and the lamprey. Furthermore, RA, driving the expression of Hox4 genes like in amniotes, regulates the anterior pronephros boundary in the catshark. We find no evidence for the involvement of this regulatory hierarchy in the AP positioning of the lamprey pronephros and the amphioxus pronephros homolog, Hatschek’s nephridium. This suggests that despite the conservation of Pax2 and Lim1 expressions in chordate pronephros homologs, the responsiveness of the IM, and hence of pronephric genes, to RA- and Hox-dependent regulation is a gnathostome novelty.

A rare specimen of Parmaturus melanobranchus was collected from the South China Sea. The complete mitochondrial genome of the specimen was sequenced using Illumina Hiseq platform and assembled with...

Plastic pollution has increased dramatically worldwide and is having a detrimental effect on a variety of marine organisms. This study contributes to the existing data on the ingestion of both macroplastics and microplastics by one elasmobranch species, the small-spotted catshark (Scyliorhinus canicula), considering the occurrence in males and females. Plastics were extracted from the stomach and spiral valve of (N = 200, n = 100 females and n = 100 males) and analysed by visual observations. A total of 28 pieces of plastic were found with five pieces extracted from a single individual. Overall findings indicate that this shark species is vulnerable to some extent to plastic ingestion (6.5% frequency of occurrence), but different aspects, such as differences in plastic contamination levels of different locations and ability to regurgitate stomach content, may affect the results of similar studies.

Background Vertebrates are characterized by possession of hypobranchial muscles (HBMs). Cyclostomes, or modern jawless vertebrates, possess a rudimentary and superficial HBM lateral to the pharynx, whereas the HBM in jawed vertebrates is internalized and anteroposteriorly specified. Precursor cells of the HBM, marked by expression of Lbx1, originate from somites and undergo extensive migration before becoming innervated by the hypoglossal nerve. How the complex form of HBM arose in evolution is relevant to the establishment of the vertebrate body plan, but despite having long been assumed to be similar to that of limb muscles, modification of developmental mechanisms of HBM remains enigmatic. Results Here we characterize the expression of Lbx genes in lamprey and hagfish (cyclostomes) and catshark (gnathostome; jawed vertebrates). We show that the expression patterns of the single cyclostome Lbx homologue, Lbx-A, do not resemble the somitic expression of mammalian Lbx1. Disruption of Lbx-A revealed that LjLbx-A is required for the formation of both HBM and body wall muscles, likely due to the insufficient extension of precursor cells rather than to hindered muscle differentiation. Both homologues of Lbx in the catshark were expressed in the somitic muscle primordia, unlike in amniotes. During catshark embryogenesis, Lbx2 is expressed in the caudal HBM as well as in the abdominal rectus muscle, similar to lamprey Lbx-A, whereas Lbx1 marks the rostral HBM and pectoral fin muscle. Conclusions We conclude that the vertebrate HBM primarily emerged as a specialized somatic muscle to cover the pharynx, and the anterior internalized HBM of the gnathostomes is likely a novelty added rostral to the cyclostome-like HBM, for which duplication and functionalization of Lbx genes would have been a prerequisite.

As far as is known, in this paper the first case of lacking of skin-related structures (epidermis, stratum laxum, dermal denticles and teeth) in a free-swimming elasmobranch, the blackmouth catshark, Galeus melastomus, is reported. The individual was caught by trawl in Sardinian waters (central-western Mediterranean) in July 2019 at a depth of 500 m. Although this kind of morphological abnormality is potentially fatal, the observations suggested that the specimen was in good health and well developed.

The presence of claspers is one of the main characteristics of the cartilaginous fishes, but its variations across taxa have received limited use in shark systematics and have generally been neglected in descriptions of species. Clasper descriptions are available only for a few catshark species and most of these are focused only in external morphology. Besides that, divergences regarding the identification of some structures persist in the literature emphasizing the need of more encompassing morphological comparative analyses on claspers of scyliorhinids. In this study, claspers structures of almost all catshark genera were examined, described, and illustrated (except Akheilos and Pentanchus) and comments on their phylogenetic significance are provided. Some characters such as degree of development of rhipidions and terminal dermal cover, occurrence, position and size of accessory marginal and terminal cartilages proved to be useful for taxonomic purposes and their significance along carcharhiniforms systematics needs to be further investigated. RESEARCH HIGHLIGHTS: Clasper morphology of catsharks is described and compared and its systematic significance is discussed here. External morphology and skeleton components of claspers vary widely among scyliorhinids and may be useful in phylogenetic analyses.

Cartilaginous fish have a comparatively short intestine known as the spiral intestine that is comprised of a helical spiral of intestinal mucosa. However, morphological and functional development of the spiral intestine is not well described. Unlike teleosts, cartilaginous fish are characterized by an extremely long developmental period in ovo or in utero for example; in the oviparous cloudy catshark (Schyliorhinus torazame), the developing fish remains inside the egg capsule for up to six months, suggesting that the embryonic intestine may become functional prior to hatch. In the present study, we describe the morphological and functional development of the spiral intestine in the developing catshark embryo. Spiral formation of embryonic intestine was completed at the middle of stage 31, prior to “pre-hatching”, which is a developmental event characterized by the opening of egg case occurring at the end of the first third of development. Within 48 hours after pre-hatching event, egg yolk began to flow from the external yolk sac into the embryonic intestine via the yolk stalk. At the same time, there was a rapid increase in mRNA expression of the peptide transporter pept1 and neutral amino acid transporter slc6a19. Secondary folds in the intestinal mucosa and microvilli on the apical membrane appeared after pre-hatching, further supporting the onset of nutrient absorption in the developing intestine at this time. We demonstrate the acquisition of intestinal nutrient absorption at the pre-hatching stage of an oviparous elasmobranch.

10 pages, 5 figures, 6 tables, supplementary material https://doi.org/10.1016/j.dsr.2018.09.010, The study of the feeding ecology of marine predators is crucial to understanding their ecological roles and advancing our knowledge of marine ecosystem functioning, especially in highly human-impacted areas. Here, we examined the trophic ecology of three abundant demersal sharks, the velvet belly lantern shark Etmopterus spinax, the blackmouth catshark Galeus melastomus and the small-spotted catshark Scyliorhinus canicula, and the rare kitefin shark Dalatias licha of the western Mediterranean Sea. Data were obtained from two deep-water areas with different degrees of human impact: a fishery restricted area (FRA) in the Gulf of Lions and a highly human-impacted area in the Catalan Sea (non-FRA). We combined analyses of individual stomach contents and stable isotope values from different individuals of each shark species. Our results revealed that D. licha is a predator located higher up on the food web, while G. melastomus, E. spinax and S. canicula are located in lower trophic positions. These results confirm that shark species play important and, most likely, complementary roles as predators in the western Mediterranean Sea. Results also revealed that despite some differences in the diet of the shark species, as revealed by the stomach contents, in the long term (isotopic results) the four species showed similar diet habits and similar trophic relationships in both FRA and non-FRA. This may be due to the fact that despite the fishing regulations in the FRA area, the population of the prey species probably do not vary between the two areas. Overall, this study provides new insights into the trophic ecology of these sharks and contributes to an understanding of their ecological roles within the community, CB was supported by a predoctoral fellowship CONICYT- Becas Chile. JN was supported by the Spanish National Program Ramón y Cajal (RYC-2015-17809). This study is a contribution to the project ECOTRANS (CTM2011-26333, Spanish Ministry of Economy and Competiveness, Spain)

Radial glial cells (RGCs) are the first cell populations of glial nature to appear during brain ontogeny. They act as primary progenitor (stem) cells as well as a scaffold for neuronal migration. The proliferative capacity of these cells, both in development and in adulthood, has been subject of interest during past decades. In contrast with mammals where RGCs are restricted to specific ventricular areas in the adult brain, RGCs are the predominant glial element in fishes. However, developmental studies on the RGCs of cartilaginous fishes are scant. We have studied the expression patterns of RGCs markers including glial fibrillary acidic protein (GFAP), brain lipid binding protein (BLBP), and glutamine synthase (GS) in the telencephalic hemispheres of catshark (Scyliorhinus canicula) from early embryos to post-hatch juveniles. GFAP, BLBP and GS are first detected, respectively, in early, intermediate and late embryos. Expression of these glial markers was observed in cells with radial glia morphology lining the telencephalic ventricles, as well as in their radial processes and endfeet at the pial surface and their expression continue in ependymal cells (or tanycytes) in early juveniles. In addition, BLBP- and GS-immunoreactive cells morphologically resembling oligodendrocytes were observed. In late embryos, most of the GFAP- and BLBP-positive RGCs also coexpress GS and show proliferative activity. Our results indicate the existence of different proliferating subpopulations of RGCs in the embryonic ventricular zone of catshark. Further investigations are needed to determine whether these proliferative RGCs could act as neurogenic and/or gliogenic precursors. This work was supported by the Spanish Ministerio de Economía y Competitividad-FEDER (BFU2014-5863-1P); Xunta de Galicia-FEDER, Grant number: Rede Galega INBIOEST ED341D R2016/032 SI

A new species of the genus Planonasus is described from off southwestern India and Sri Lanka in the northern Indian Ocean. The new species occurs along the upper continental slope from 200 to 1000 m deep and was landed in fisheries for gulper sharks (Centrophorus spp.). Planonasus indicus sp. n. externally closely resembles P. parini (Carcharhiniformes: Pseudotriakidae), the only other member of the genus. It can be distinguished from P. parini by a combination of morphological characters including absence of oral papillae, lack of a distinct white mark on the free rear tip of the first dorsal fin, sides and underside of head, as well as fin edges that are similar in color as body (vs. dusky), more tooth rows in the lower jaw, shorter labial furrows, longer and less high spiracles, proportionally higher, more angular dorsal fins, especially the second dorsal fin, proportionally longer pectoral fins, a proportionally larger anal fin, longer distances from the snout tip to the origins of the caudal fin, both dorsal fins and the pelvic fins, as well as to the vent, and shorter distances for preorbital snout, prepectoral length, pelvic midpoint to second dorsal fin origin, and pelvic-anal space. A revised diagnosis of the genus and key to the family is also provided.

Background Studying cartilaginous fishes (chondrichthyans) has helped us understand vertebrate evolution and diversity. However, resources such as genome sequences, embryos, and detailed staging tables are limited for species within this clade. To overcome these limitations, we have focused on a species, the brownbanded bamboo shark (Chiloscyllium punctatum), which is a relatively common aquarium species that lays eggs continuously throughout the year. In addition, because of its relatively small genome size, this species is promising for molecular studies. Results To enhance biological studies of cartilaginous fishes, we establish a normal staging table for the embryonic development of the brownbanded bamboo shark. Bamboo shark embryos take around 118 days to reach the hatching period at 25°C, which is approximately 1.5 times as fast as the small-spotted catshark (Scyliorhinus canicula) takes. Our staging table divides the embryonic period into 38 stages. Furthermore, we found culture conditions that allow early embryos to grow in partially opened egg cases. Conclusions In addition to the embryonic staging table, we show that bamboo shark embryos exhibit relatively fast embryonic growth and are amenable to culture, key characteristics that enhance their experimental utility. Therefore, the present study is a foundation for cartilaginous fish research. Developmental Dynamics 247:712-723, 2018. © 2017 Wiley Periodicals, Inc.

Intersexual differences in morphometrics were investigated in five species of the catshark genus Scyliorhinus. ANCOVA was used to test 59 measurements, considering capture location and total length as covariates. In all examined species, pelvic-anal distances and pelvic-fin inner margin lengths were greater in males than in females, representing a clear pattern for the genus.

Kelp forests are associated with high biodiversity as they provide habitat and food source for many species. Redspotted catshark Schroederichthys chilensis is a coastal shark species associated with kelp forests of southern South America dominated by Lessonia trabeculata. Despite its common occurrence redspotted catshark the knowledge on its trophic ecology is rudimentary. This study aimed to assess the effects of presence/absence of kelp L. trabeculata on the isotopic niche of redspotted catshark through comparison of δ13C and δ15N in its blood and fin tissues (non-lethal samples). We found that males were characterized by higher trophic position and enriched carbon sources compared to females in locations where kelp was present. In contrast, males and females were characterized by similar isotopic niche in absence of kelp. These differences are most probably an effect of higher prey diversity associated with microhabitats generated by kelp forests that allow sexual segregation of isotopic niche. Therefore, extensive kelp harvest may cause significant effects in isotopic niche and nutritional status of adult redspotted catshark and may negatively affect its populations.

Physiology Embryonic sharks grow within external cases that are often translucent. In response to signs of predators, the embryos of several shark species become motionless (or “freeze”). The amount of time that they can remain still is limited by their need for oxygen exchange stimulated by their movement. Ripley et al. exposed small-spotted catshark embryos to water at 15° and 20°C, and found that the time they could remain motionless was reduced by sevenfold at the higher temperature. Although the precise mechanism was not clear, the authors conclude that this was in part a result of higher metabolic requirements at higher temperatures. Thus, the ability to “freeze” at higher temperatures may be compromised, leading to higher rates of predation in warmer oceans. Conserv. Physiol. 9 , coab045 (2021).

Our aim is to contribute to the valorization and optimization of a salted-dried seafood product prepared from small-spotted catshark (Scyliorhynus canicula) akin to “litao seco,” the high-priced, traditional dried blackmouth catshark (Galeus melastomus). This work focused on studying the changes in physicochemical and microbiological parameters of S. canicula salted (for 3 h or 24 h) and dried (convection oven for 24 h or tray drier for 3 h). As expected, salting and drying reduced the water content and water activity, while chloride content in fillets increased. Also, significant but distinct changes in color, namely CIE L* and b*, were observed. Total viable counts were significantly reduced in the salted-dried shark, but the later still presented Staphylococcus aureus, though at marginally acceptable, non-hazardous levels. The abundance of yeasts was reduced by 3 log(cfu/g) in samples oven-dried for 24 h but only by 0.8 log after 3 h in the tray-drier. From our results, salted-dried S. canicula...

Egg cases of the narrowmouthed catshark Schroederichthys bivius were recorded entangled with sponges, corals and tubeworms at different sites in the south-west Atlantic Ocean. This work sheds light on the importance of benthic invertebrates in the life cycle of oviparous chondrichthyan species.

This study concerns the cephalopod species that are part of the diet of the small-spotted catshark Scyliorhinus canicula and the longnose spurdog Squalus blainville sampled by commercial trawlers in the Aegean Sea from 2005 to 2012. Based on the examined cephalopod beaks, 15 species were identified belonging in six families of Teuthida, one of Sepiida and two of Octopoda. The diversity of cephalopod prey species was higher for S. canicula (N = 15) than for S. blainville (N = 10). Nektonic cephalopods comprised the majority (>72%) of the preyed species by both sharks, among which about 55% inhabit the demersal zone and 45% the mesopelagic. In the diet of S. canicula, the demersal squid Illex coindetii and the pelagic sepiolid Heteroteuthis dispar were equally represented composing 20% of prey specimens, followed by the small-sized squid Abralia veranyi and the demersal sepiolid Rossia macrosoma. The latter species was substituted in the diet of S. blainville by the demersal medium-sized octopod Scaeurgus unicirrhus, which with the equally represented three other species, composed 50% of the cephalopod prey. Differences observed between S. canicula and S. blainville in the condition of beaks retained in their stomach contents and in the variation of prey species diversity by predator specimen size, may imply differences in their foraging tactics (hunting for prey vs scavenging on the bottom), habitats and stomach evacuation frequency.

The parasitic fauna of the small-spotted catshark,Scyliorhinus caniculain the north-eastern Aegean Sea was investigated. Twenty-one out of the 52 (prevalence 40.4%) specimens collected were found infected with parasites; an arthropod and two nematode genera. Seven specimens (prevalence 13.5%) were infected by aNeoalbionellasp. copepod. Ten and 14 specimens were infected by the nematodesProleptus obtusus(prevalence 19.2%) andAnisakissp. (prevalence 26.9%), respectively. FemaleS. caniculaspecimens were significantly more heavily infected during autumn and when the whole sampling period is considered. Nematode infection was significantly related to season, becoming progressively heavier from spring to autumn. No correlation was found between TL of specimens and number of parasites for males or females, irrespective of gender. The present study provided a first record ofNeoalbionellasp.,P. obtususandAnisakissp. infections ofS. caniculain the north-eastern Mediterranean. The lower prevalence ofProleptus obtususand the higher prevalence ofAnisakissp. infection recorded in this study may be due to prey availability and parasite populations in this locality.

Occurrence, abundance and size trends of 25 demersal Chondrichthyes (10 Sharks: 3 Carcharhiniformes, 2 Hexanchiformes, 5 Squaliformes; 14 Batoids: 3 Myliobatiformes, 8 Rajiformes, 3 Torpediniformes and 1 Holocephalan: 1 Chimaeriformes) collected from 22 years (1994–2015) of Mediterranean International Trawl Surveys (MEDITS) around Sardinian seas, were given. Data relative to two strata, the continental shelf (10–200 m), the slope (201–800 m), and the overall (10–800 m), were analyzed in order to identify the general species distribution of their habitat preference. From the gathered data it appeared that the shelf was mostly inhabited by batoids while the slope by sharks. Only the small-spotted catshark Scyliorhinus canicula and the thornback skate Raja clavata were equally distributed with high values of occurrence and abundance both in the shelf and in the slope. All the other species showed a preferential distribution only in one stratum (shelf or slope). In general, temporal trends of abundance indexes were stable or increasing in all strata. GAM analysis also confirmed a stable trend. Almost all species displayed stable in size structure analysis, apart from R. brachyura and Dipturus oxyrinchus that showed a statistically increasing trend. Although the investigated chondrichthyan species seemed to display a not alarming status of conservation in Sardinian seas, more investigation should be done to assure a proper management of this threatened resource.

In every jawed vertebrate species studied so far, the T cell receptor (TCR) complex is composed of two different TCR chains (α/β or γ/δ) and a number of CD3 subunits responsible for transmitting signals into the T cell. In this study, we characterised all of the TCR and CD3 genes of small-spotted catshark (Scyliorhinus canicula) and analysed their expression in a broad range of tissues. While the TCR complex is highly conserved across jawed vertebrates, we identified a number of differences in catshark, most notably the presence of two copies of both TCRβ and CD3γδ, and the absence of a functionally-important proline rich region from CD3ε. We also demonstrate that TCRβ has duplicated independently multiple times in jawed vertebrate evolution, bringing additional diversity to the TCR complex. This study reveals new insights about the evolutionary history of the TCR complex and raises new avenues for future exploration.

Mediterranean young-fish oriented experimental bottom trawl surveys represent a precious source of information on both past and current standing stocks and their life history traits and exploitation state. In the present note, taking the occasion of the same vessel employed in the South of Sicily (Central Mediterranean), an indirect approach has been implemented to compare MEDITS (Mediterranean International Bottom Trawl Survey) and GRUND (Gruppo Nazionale Demersali) abundance and biological features of the blackmouth catshark Galeus melastomus Rafinesque, 1810 to highlight gear and season effects if any. Data were gathered between 1994 and 2006, in spring-summer (MEDITS) and autumn (GRUND). The density and biomass indexes and occurrences were substantially lower in spring than in autumn. On the contrary, the biological traits were more similar, although significant differences were detected in the length frequency distribution. The homogeneity of life traits between seasons and the critical features showed in this study demonstrate that an annual experimental trawl survey can be enough to monitor G. melastomus. Similar analysis could be useful to highlight seasonal and gear effects on the other demersal stocks to better figure out limits and possibility of Mediterranean young-fish oriented experimental bottom trawl surveys data.

The diet of the small-spotted catshark Scyliorhinus canicula, captured in the Aegean Sea by bottom-trawl from 2006 to 2012, was investigated with respect to sex, maturity condition, sampling location and season. The stomach contents of 432 specimens, measuring from 144 to 517 mm in total length, were analysed. The cumulative prey curve showed that the sample size was adequate to describe the species’ diet, which was quantified using the percentage gravimetric composition (%W). The identified prey items belonged to eight major groups: Teleostei, Chondrichthyes, Crustacea, Cephalopoda, Annelida, Echinodermata, phanerogams and macroalgae, with Teleostei, Crustacea and Cephalopoda being the most consumed in both females (%W = 48.1, 16.0 and 31.4, respectively) and males (%W = 33.9, 31.6 and 29.8, respectively). Higher diet diversity was observed in males than females, in immature individuals than mature ones, regardless of sex, as well as in spring in comparison to autumn and winter. Feeding intensity...

We present the first mitochondrial genome of a South African endemic catshark, Poroderma pantherinum. The complete mitogenome is 16,686 bp in length, comprising 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and one non-coding control region. Similar to other shark mitogenomes, it is AT rich (61.1%), with a GC content of 38.9%. Protein-coding genes used one of two start codons (ATG and GTG) and one stop codon (TAA/TA-/T-). Phylogenetic analysis of the leopard catshark and 34 carcharhinid species showed that it clusters with two other scyliorhinid species (Cephaloscyllium umbratile and Scyliorhinus canicula) with 100% support.

Elasmobranchs are key to a healthy marine ecosystem but are under threat from human activities, such as destructive fisheries and shark finning. Embryos of oviparous elasmobranchs may be further challenged during development by rising temperatures and falling dissolved oxygen concentrations in their intertidal environment. However, the impact of climate change on survival and growth of oviparous elasmobranchs is still poorly understood. Here, we investigate the effects of temperature and hypoxia on the growth and survival of small‐spotted catshark (Scyliorhinus canicula) embryos by incubating eggs in either: normoxia 15 °C, normoxia 20 °C, hypoxia 15 °C, or hypoxia 20 °C. Incubation under the elevated temperature increased the embryonic growth rate, yolk consumption rate, and Fulton's condition factor at hatching, whilst decreasing the total length and body mass of newly hatched sharks. Under low oxygen conditions (50 % air saturation) the survival rate of S. canicula embryos dropped significantly, and the temperature induced increase in Fulton's condition factor was reversed. Together, these data demonstrate both the individual and compound effects of elevated temperature and hypoxia on the survival and growth during early ontogeny of a ubiquitous, coastal elasmobranch, S. canicula.

A new genus and species of catshark is described based on a single specimen collected off Ambon in the Maluku Islands of eastern Indonesia. Akheilos suwartanai belongs to the subfamily Schroederichthyinae which differs from the other catsharks in a combination of: similar sized dorsal fins, supraorbital crests present, pseudosiphon present on claspers, broad subocular ridges under eyes, posterior nasal flaps present, tips of rostral cartilage fused into a rostral node. It represents the first record of this subfamily outside of the Americas. Akheilos differs from the other genus in the subfamily, Schroederichthys in a combination of: clasper groove not fused dorsally, ventral lobe of caudal fin produced, more intestinal valve turns, anal fin slightly larger than second dorsal fin, and in colour pattern.

This study highlights plastics occurrence in five demersal fish species from the Southern Tyrrhenian Sea: the Red mullet Mullus barbatus barbatus, the Piper gurnard Trigla lyra, the Blackmouth catshark Galeus melastomus, the Lesser spotted dogfish Scyliorhinus canicula and the Brown ray Raja miraletus. Overall, 125 fish were examined: 21 Red mullets, 16 Piper gurnards, 75 Blackmouth catsharks, 72 Dogfish and 1 Brown ray. The percentage of fish with ingested plastics was 14.4% with 0.24 items per specimen. The majority of the debris were fibers and the application of infrared and Raman spectroscopy allowed the identification and discrimination of plastic and non-plastic fibers. The plastic debris isolated were mainly microplastics (94.1%), while macroplastics occurrence was very low (5.9%). The plastics were identified as polypropylene, Teflon, nylon, kraton G (triblock copolymer) and polyethylene. Also cellulose was detected. S. canicula was the species with the highest number of plastic pollutants.

The catshark genus Scyliorhinus belongs to the family Scyliorhinidae, the most diverse family of sharks, and currently presents 16 valid species according to most modern accounts. The long history of taxonomic rearrangements and inaccurate descriptions of many species have contributed to misidentification of specimens and lack of information on the distributional range and diagnostic characters of its species. Species of Scyliorhinus are reviewed and redescribed here, with detailed descriptions on external morphology, neurocranium, claspers, dermal denticles, and tooth morphology provided for the first time for all species. Sixteen species are recognized as valid: Scyliorhinus boa (Goode & Bean, 1896), S. cabofriensis Soares, Gomes & de Carvalho, 2016, S. canicula (Linnaeus, 1758), S. capensis (Müller & Henle, 1838), S. cervigoni Maurin & Bonnet, 1970, S. comoroensis Compagno, 1988, S. duhamelii (Garman, 1913), S. garmani (Fowler, 1934), S. haeckelii (Miranda Ribeiro, 1907), S. hesperius Springer, 1966, S. meadi Springer, 1966, S. retifer (Garman, 1881), S. stellaris (Linnaeus, 1758), S. torazame (Tanaka, 1908), S. torrei Howell-Rivero, 1936, and S. ugoi Soares, Gomes & Gadig, 2015. The main taxonomic decisions herein taken include the resurrection of S. duhamelii (previously a junior synonym of S. canicula) and the synonimization of S. tokubee with S. torazame. Information on geographic distribution was updated for most species, especially for those with wide ranges (S. canicula, S. haeckelii, S. retifer, and S. stellaris).

Most extant vertebrates display a high variety of tooth and tooth-like organs (odontodes) that vary in shape, position over the body and nature of composing tissues. The development of these structures is known to involve similar genetic cascades and teeth and odontodes are believed to share a common evolutionary history. Gene expression patterns have previously been compared between mammalian and teleost tooth development but we highlight how the comparative framework was not always properly defined to deal with different tooth types or tooth developmental stages. Larger-scale comparative analyses also included cartilaginous fishes: sharks display oral teeth and dermal scales for which the gene expression during development started to be investigated in the small-spotted catshark Scyliorhinus canicula during the past decade. We report several descriptive approaches to analyse the embryonic tooth and caudal scale gene expressions in S. canicula. We compare these expressions wih the ones reported in mouse molars and teleost oral and pharyngeal teeth and highlight contributions and biases that arise from these interspecific comparisons. We finally discuss the evolutionary processes that can explain the observed intra and interspecific similarities and divergences in the genetic cascades involved in tooth and odontode development in jawed vertebrates.

In this study, we exposed twelve specimens of small-spotted catshark (Scyliorhinus canicula) to biological and anthropogenic sounds in order to assess their behavioural changes potentially referable to pray presence and masking effect due to the shipping noise. Specifically, the sharks held individually in aquarium were exposed to four acoustic experimental conditions differentiated in their spectral (Hz) components (biological and anthropogenic mixed sources) and intensity (dB re 1 μPa) levels. Swimming behaviour and spatial distribution of the specimens were recorded. The results highlighted significant differences in time spent in swimming and in spatial use of the aquarium among the experimental conditions. The sharks concentrated their swimming behaviour in the aquarium’s lower sections when the intensity levels of the biological acoustic sources were higher than the anthropogenic ones. Conversely, when the intensity levels of the anthropogenic sources were higher than the biological, the specimens showed the highest values of time spent in swimming. In conclusion, this study hypothesised that the environmental soundscape could play an important role in the catshark prey-predator relationship and that the impact of masking effect can depend on the acoustic intensity levels.In this study, we exposed twelve specimens of small-spotted catshark (Scyliorhinus canicula) to biological and anthropogenic sounds in order to assess their behavioural changes potentially referable to pray presence and masking effect due to the shipping noise. Specifically, the sharks held individually in aquarium were exposed to four acoustic experimental conditions differentiated in their spectral (Hz) components (biological and anthropogenic mixed sources) and intensity (dB re 1 μPa) levels. Swimming behaviour and spatial distribution of the specimens were recorded. The results highlighted significant differences in time spent in swimming and in spatial use of the aquarium among the experimental conditions. The sharks concentrated their swimming behaviour in the aquarium’s lower sections when the intensity levels of the biological acoustic sources were higher than the anthropogenic ones. Conversely, when the intensity levels of the anthropogenic sources were higher than the biological, the specimens s...

The small-spotted catshark is one of the most abundant elasmobranchs in the Northeastern Atlantic Ocean. Although its landings are devoted for human consumption, in general this species has low commercial value with high discard rates, reaching 100% in some European fisheries. The reduction of post-harvest losses (discards and by-products) by promotion of a full use of fishing captures is one of the main goals of EU fishing policies. As marine collagens are increasingly used as alternatives to mammalian collagens for cosmetics, tissue engineering, etc., fish skins represent an excellent and abundant source for obtaining this biomolecule. The aim of this study was to analyze the influence of chemical treatment concentration, temperature and time on the extractability of skin collagen from this species. Two experimental designs, one for each of the main stages of the process, were performed by means of Response Surface Methodology (RSM). The combined effect of NaOH concentration, time and temperature on the amount of collagen recovered in the first stage of the collagen extraction procedure was studied. Then, skins treated under optimal NaOH conditions were subjected to a second experimental design, to study the combined effect of AcOH concentration, time and temperature on the collagen recovery by means of yield, amino acid content and SDS-PAGE characterization. Values of independent variables maximizing collagen recovery were 4 °C, 2 h and 0.1 M NaOH (pre-treatment) and 25 °C, 34 h and 1 M AcOH (collagen extraction)., This research was funded by EU INTERREG_POCTEP 2015, 0302_CVMAR_I_1_P; EU-INTERREG Atlantic Area Programme, EAPA_151/2016; Xunta de Galicia, IN607B 2018/19), We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI), Publisher's version

This contribution contains 3D models of the cranial skeleton and muscles in an elephantfish (Callorhinchus milii) and a catshark (Scyliorhinus canicula), based on synchrotron tomographic scans. These datasets were analyzed and described in Dearden et al. (2021) "The morphology and evolution of chondrichthyan cranial muscles: a digital dissection of the elephantfish Callorhinchus milii and the catshark Scyliorhinus canicula." Journal of Anatomy.

The population composition and aspects of the reproductive biology of 452 blackmouth catsharks, Galeus melastomus were investigated. The sharks were incidentally caught off the North-Western Aegean, the Eastern Corinthian and Northern Euboean Gulfs by commercial bottom trawlers and longlines at depths between 200 and 500 m. The overall sex ratio (1:1.1 females:males) was not different from the theoretical unit (1:1). No differences in the sex ratios were detected among seasons, areas or depth strata. Significant differences in the population structure regarding different maturity stage proportions at different seasons, fishing areas and depths, were observed. The sampled population mainly consisted of immature catsharks (77%), predominantly trawled off the NW Aegean and Corinthian Gulf during winter and autumn. Fifteen per cent of the samples, mainly captured in spring and summer off the N Euboean Gulf, were mature. Eight per cent of the specimens was found to be maturing. Higher frequencies of heavier female individuals were observed. Based on the maturation ogives and the total lengths (TL) for each sex, using logistic regression which presented sex-related differences, male Galeus melastomus achieved maturity at 433.6 mm while females at 483.5 mm. The number of egg capsules in the oviducts spanned from 1–12 per female with sizes varying from 38 × 14 mm to 55 × 20 mm. This is the first study investigating the demography and aspects of Galeus melastomus reproduction in the Eastern Mediterranean.

Batoidea (rays and skates) is a monophyletic subgroup of elasmobranchs that diverged from the common ancestor with Selachii (sharks) about 270 Mya. A larger number of batoids can adapt to low-salinity environments, in contrast to sharks, which are mostly stenohaline marine species. Among osmoregulatory organs of elasmobranchs, the kidney is known to be dedicated to urea retention in ureosmotic cartilaginous fishes. However, we know little regarding urea reabsorbing mechanisms in the kidney of batoids. Here, we performed physiological and histological investigations on the nephrons in the red stingray (Hemitrygon akajei) and two shark species. We found that the urine/plasma ratios of salt and urea concentrations in the stingray are significantly lower than those in cloudy catshark (Scyliorhinus torazame) under natural seawater, indicating that the kidney of stingray more strongly reabsorbs these osmolytes. By comparing the three-dimensional images of nephrons between stingray and banded houndshark (Triakis scyllium), we showed that the tubular bundle of stingray has a more compact configuration. In the compact tubular bundle of stingray kidney, the distal diluting tubule was highly developed and frequently coiled around the proximal and collecting tubules. Furthermore, co-expression of NKAα1 (Na+/K +-ATPase) and NKCC2 (Na+- K+-2Cl– cotransporter 2) mRNAs was prominent in the coiled diluting segment. These findings imply that NaCl reabsorption is greatly facilitated in the stingray kidney, resulting in a higher reabsorption rate of urea. Lowering the loss of osmolytes in the glomerular filtrate is likely favorable to the adaptability of batoids to a wide range of environmental salinity.

Plastics are widely diffused in the oceans and their ingestion by marine organisms is raising concern for potentially adverse effects. The risk of harmful interactions with marine plastic pollution depends on the biology of the species as well as the distribution and abundance of the different plastic types. The aim of this study was to assess the occurrence of plastic ingestion by the small-spotted catshark (Scyliorhinus canicula), one of the most abundant elasmobranchs in the Mediterranean Sea. The expression levels of genes indicative of total immune system function were analyzed to gather preliminary data for further investigation of any potential correlations between plastic presence and immune activation. One hundred catsharks were collected during the Spring 2018 in two geographic locations in the southern region of the central Mediterranean Sea: 1) near Mazara del Vallo, SW Sicily and 2) near Lampedusa island, Italy's southernmost. Standard measurements were recorded for each specimen and its organs and sex was determined. The gastrointestinal tract (GIT) was preserved for plastic detection and identification. Where present, plastics (macro- and micro-) were characterized in terms of size, shape and polymer typology through microscopy and μ-Raman spectroscopy. Spleen from a subset of thirty samples was preserved for RNA extraction, then used to quantify by real time PCR the transcripts of T cell receptor beta (TCRB), T cell receptor delta (TCRD) and IgM genes. The results indicated that ingestion of plastic is widespread, with microplastics (MP, from 1 μm to 1 cm) in approximately 18% of the specimens collected. A significant increase in the expression of TCRB, TCRD and IgM was observed in the spleen of MaP + specimens from Mazara del Vallo waters, in parallel with 67% increase in liver weight. While the presence of MP alone is not enough to induce a strong activation of the immunity, some type of plastics falling into the MaP category may be more toxic than others and crucial in the activation of the immune response. The results of this study represent a first evidence that plastic pollution represents an emerging threat to S. canicula, the Mediterranean food web and human consumers.

Schroederichthys saurisqualus is a small shark endemic to the southwestern Atlantic, with known distribution on the upper continental slope of southern Brazil, ranging between 122 and 435 m in depth, where it is a trawling bycatch component. In the present study, 124 S. saurisqualus specimens collected between 280 and 500 m in depth from September to October 2002 were analyzed concerning reproductive and feeding aspects. Specimen sizes ranged from 252 to 610 mm total length (TL) for males and 280 to 602 mm TL for females. All males larger than 550 mm TL presented calcified claspers, while seven females (524 to 602 mm TL) presented forming eggs. The data reported herein indicate a first maturity size of about 500 mm TL for both males and females. Stomach content analysis identified the squid Illex argentinus as the most frequent prey, observed in 76.86% of the examined stomachs. The results indicate that S. saurisqualus displays a mate-finding strategy during the reproductive season, when squid predation ocurrs. However, this behavior puts this small catshark population in a vulnerable situation, since intense squid trawling activities are noted during the same period in the same area, exposing the local juvenile S. saurisqualus population to higher fishing pressures.

In amniotes, limb muscle precursors de-epithelialize from the ventral dermomyotome and individually migrate into limb buds. In catsharks, Scyliorhinus, fin muscle precursors are also derived from the ventral dermomyotome, but shortly after de-epithelialization, they reaggregate within the pectoral fin bud and differentiate into fin muscles. Delamination of muscle precursors has been suggested to be controlled by hepatocyte growth factor (HGF) and its tyrosine kinase receptor (MET) in amniotes. Here, we explore the possibility that HGF/MET signaling regulates the delamination of appendicular muscle precursors in embryos of the catshark Scyliorhinus canicula. Our analysis reveals that Hgf is expressed in pectoral fin buds, whereas c-Met expression in fin muscle precursors is rapidly downregulated. We propose that alteration of the duration of c-Met expression in appendicular muscle precursors might underlie the evolution of individually migrating muscle precursors, which leads to the emergence of complex appendicular muscular systems in amniotes.

This study is a contribution to the project ECOTRANS (CTM2011-26333, Spanish Ministry of Economy and Competiveness, Spain).-- 8 pages, 5 figures, 4 tables, Studying the feeding ecology of an organism is essential to understanding its ecological role in the ecosystem. Although the small-spotted catshark (Scyliorhinus canicula) is widely studied, most feeding studies have been conducted using invasive techniques, such as the analysis of stomach contents. Moreover, information from the Mediterranean Sea is surprisingly scarce and not up to date. Here, we studied the feeding ecology of the small-spotted catshark in the northwestern Mediterranean Sea using stable isotopes (nitrogen and carbon isotopic values) from blood samples, with individuals released alive in the area of capture after sampling. In overall for the population of small-spotted catshark, the isotopic values were −19.01 ± 1.12‰ and 8.03 ± 0.61‰ for δC and for δN, respectively. Results reveal a diet mainly composed of euphausiids, with sex and size variations. Results confirm the ecological role of the small-spotted catshark as a mesopredator, which holds a trophic position similar to skates and rays in the study area, but lower than the other demersal and pelagic sharks analysed. The trophic behaviour of the small-spotted catshark indicates its high trophic plasticity, which could allow this species to thrive in highly exploited environments. Our methodological approach, which did not damage the target species, presents new possibilities for conducting ecological studies with other elasmobranchs in the Mediterranean Sea, a highly exploited area that hosts many threatened and rare species, CB was supported by a predoctoral fellowship CONICYT- Becas Chile. JN was supported by the Andalucía Talent Hub Program (Andalusian Knowledge Agency of the Junta de Andalucía, European Union's Seventh Framework Program and Marie Skłodowska-Curie actions - 267226)