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Environmental conditions have a significant influence on the physiological processes that regulate the reproduction of fish. However, there is less information on this subject for chondrichthyans, and particularly for males. This study describes the spermatogenic cycle of the narrownose smooth hound shark Mustelus schmitti related to sex steroid plasma levels and the potential influences of photoperiod and temperature as reproductive cues. A total of 70 males were caught bi-monthly for over a year in the coastal waters of Argentina. Testicular samples were taken for histological characterization and blood samples were taken for the measurement of testosterone (T) and progesterone (P 4 ) plasma levels from each male. Bottom temperature was recorded at each sampling point and the daily photoperiod was estimated from Julian Day Calendar. Histological assessment revealed that the complete cycle of spermatogenesis in M. schmitti lasts just over a year, with the onset of the new spermatogenic cycle (spermatocyte formation) overlapping with the end (spermiation and filling of the seminiferous ducts) of the previous cycle. This particular phase was associated with the peak in T plasma levels, which was found to be significantly explained by the increase in photoperiod in spring. The rise in temperature above 15–16 °C at the end of spring was significantly associated with a reduction in T plasma levels. Additionally, an elevation in P 4 plasma levels was observed after the photoperiod increase phase. Males would be ready to mate from mid-spring, following female parturition and just before ovulation/pregnancy.

While the general diet of Mediterranean elasmobranchs has been widely studied, little is known about food partitioning and competition among sympatric species, despite these being important forces structuring marine communities. Using stomach content and stable isotope analyses, we investigated diet and trophic levels and evaluated the diet overlap and partitioning of Scyliorhinus canicula, Mustelus mustelus, and M. punctulatus in the northwestern Adriatic Sea. These shark species were confirmed as opportunistic mesopredators, but significant differences in their diets emerged. The two bentho-demersal Mustelus species had a larger trophic overlap with S. canicula than between each other. Given the pronounced morphological similarity of these two Mustelus species, this is likely a strategy to limit competition. The strictly benthic S. canicula showed a more varied diet compared to the other species. Stable isotope analysis highlighted that despite the smaller size and overlapping diets, S. canicula occupied a slightly higher trophic level. A better characterization of the trophic role of these species in the food web of the basin can be obtained from these data. At an ecosystem level, this information is essential to evaluate the possible consequences of the decline or recovery of the population of these exploited species.

Elasmobranchs are among the species most threatened by overfishing and a large body of evidence reports their decline around the world. As they are large predators occupying the highest levels of marine food webs, their removal can alter the trophic web dynamic through predatory release effects and trophic cascade. Suitable management of threatened shark species requires a good understanding of their behaviour and feeding ecology. In this study we provide one of the first assessments of the trophic ecology of the “vulnerable” smooth-hounds Mustelus mustelus and M. punctulatus in the Central Mediterranean Sea, based on stomach contents and stable isotope analyses. Ontogenetic diet changes were addressed by comparing the feeding habits of three groups of individuals: juveniles, maturing and adults. Our results highlighted that the two species share a similar diet based mostly on the consumption of benthic crustaceans (e.g. hermit crabs). Their trophic level increases during ontogeny, with adults increasing their consumption of large-sized crustaceans (e.g. Calappa granulata , Palinurus elephas ), cephalopods (e.g. Octopus vulgaris ) and fish (e.g. Trachurus trachurus ). Our results provide also evidence of ontogenetic shifts in diet for both species showing a progressive reduction of interspecific trophic overlap during growth. The results of this study contribute to improve the current knowledge on the trophic ecology of these two threatened sharks in the Strait of Sicily, thus providing a better understanding of their role in the food web.

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

The population genetic structure and demographics of the common smoothhound shark Mustelus mustelus were investigated across 2 major oceanographic barriers along the southern African coastline: the Angola–Benguela Front and the Indian/Atlantic boundary. Population genetic structure was inferred using multilocus data generated from 8 microsatellite loci and the sequence polymorphism of a 793 bp fragment of the mitochondrial (mtDNA) ND4 gene region. Microsatellites revealed significant interoceanic genetic structure (F ST = 0.007–0.296) between the South-East Atlantic and South-West Indian Ocean, while mtDNA suggested interoceanic gene flow (pairwise φST = 0–0.288). A coalescent analysis in MIGRATE-N suggested asymmetrical gene flow that predominantly occurs from the South-West Indian to South-East Atlantic Oceans, with relatively small (<50) estimates of effective population size. Tests of selective neutrality and mismatch distribution indicated a population history consistent with a population expansion event. Contemporary restriction to gene flow is proposed to account for the present-day genetic structuring observed for M. mustelus in South Africa. Due to the vulnerable status of the species, these results should be considered in future management and conservation strategies addressing the sustainable exploitation of this fisheries resource.

Over the last century the fish community of the Dutch coastal North Sea zone has lost most its shark and skate species. Whether their disappearance has changed the trophic structure of these shallow waters has not been properly investigated. In this study historical dietary data of sharks and skates, being in the past (near)-residents, juvenile marine migrants and marine seasonal visitors of the Dutch coastal North Sea zone were analyzed for the period 1946–1954. Near-resident and juvenile marine migrant species were demersal while all marine seasonal visitors species were pelagic. Based on stomach content composition, the trophic position of four of the various shark and skate species could be reconstructed. The (near)-resident species, the lesser spotted dogfish, the marine juvenile migrant, the starry smooth hound, and the benthopelagic marine seasonal visitor, the thornback ray, had a benthic/demersal diet (polychaetes, molluscs and crustaceans), while the pelagic marine seasonal visitor, the tope shark, fed dominantly on cephalopods and fishes. Diet overlap occurred for fish (tope shark and lesser spotted dogfish), for hermit crabs (lesser spotted dogfish and starry smooth hound) and for shrimps (thornback ray and starry smooth hound). Trophic position ranged from 3.2 for thornback ray preying exclusively on crustaceans to 4.6 for the tope shark consuming higher trophic prey (crustaceans and fish). The analysis indicates that most of the shark and skate species were generalist predators. The calculated trophic positions of shark and skate species indicate that those species were not necessarily at the top of the marine ecosystem food web, but they might have been the top predators of their particular ecological assemblage.

In the experiment, crude proteins from spotless smoothhound (Mustelus griseus), cartilages were isolated by HCl-Guanidine buffer, and its hydrolysate was prepared using trypsin at pH 8.0, 40 °C with a total enzyme dose of 2.5%. Subsequently, three antioxidant peptides were purified from the hydrolysate using membrane ultrafiltration, anion-exchange chromatography, gel filtration chromatography, and reverse phase high-performance liquid chromatography. The amino acid sequences of isolated peptides were identified as Gly-Ala-Glu-Arg-Pro (MCPE-A); Gly-Glu-Arg-Glu-Ala-Asn-Val-Met (MCPE-B); and Ala-Glu-Val-Gly (MCPE-C) with molecular weights of 528.57, 905.00, and 374.40 Da, respectively, using protein amino acid sequence analyzer and mass spectrum. MCPE-A, MCPE-B and MCPE-C exhibited good scavenging activities on 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH•) (EC50 3.73, 1.87, and 2.30 mg/mL, respectively), hydroxyl radicals (HO•) (EC50 0.25, 0.34, and 0.06 mg/mL, respectively), 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radicals (ABTS+•) (EC50 0.10, 0.05, and 0.07 mg/mL, respectively) and superoxide anion radicals ( O 2 − •) (EC50 0.09, 0.33, and 0.18 mg/mL, respectively). MCPE-B showed similar inhibiting ability on lipid peroxidation with butylated hydroxytoluene (BHT) in a linoleic acid model system. Furthermore, MCPE-A, MCPE-B, and MCPE-C could protect H2O2-induced HepG2 cells from oxidative stress by decreasing the content of malonaldehyde (MDA) and increasing the levels of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and glutathione reductase (GSH-Rx). Glu, Gly, Met, and Pro in their sequences and low molecular weight could be attributed to the antioxidant activities of three isolated peptides. These results suggested that GAERP (MCPE-A), GEREANVM (MCPE-B), and AEVG (MCPE-C) from cartilage protein hydrolysate of spotless smoothhound might serve as potential antioxidants and be used in the pharmaceutical and health food industries.

Gli autori riportano la cattura di un esemplare anomalo di palombo, Mustelus mustelus (Linnaeus, 1758). L'esemplare misurava 1045 mm di lunghezza totale (TL) e pesava 3615 g. Presentava pterigopodi di morfologia diversa: quello destro normalmente sviluppato, caratteristico di un maschio adulto, e quello sinistro piu piccolo, arrotondato nella sua estremita distale, con una grande apertura sulla superficie ventrale. Lesame della cavita addominale ha rivelato l'assenza totale delľapparato genitale sul lato sinistro, il che spiega probabilmente la forma aberrante dello pterigopodio sinistro. Il rapporto tra il peso corporeo totale e la lunghezza totale ha rivelato che l'esemplare anormale era notevolmente meno pesante degli esemplari normali della stessa classe di TL.

Elasmobranchs are among the most threatened long-lived marine species worldwide, and incidental capture is a major source of mortality. The northern central Adriatic Sea, though one of the most overfished basins of the Mediterranean Sea, supports a very valuable marine biodiversity, including elasmobranchs. This study assesses the impact of the northern central Adriatic pelagic trawl fishery on common smooth-hound (Mustelus mustelus), spiny dogfish (Squalus acanthias), common eagle ray (Myliobatis aquila), and pelagic stingray (Pteroplatytrygon violacea) by examining incidental catches recorded between 2006 and 2015. The distribution of bycatch events was evaluated using geo-referenced data. Generalized Linear Models were computed to standardize the catch of the four species and to predict the relative abundance of bycatch events. Data analysis shows that most bycatch events involving all four species occurred in the northern Adriatic Sea. The models predicted significant, distinct temporal patterns of standardized catches in line with previous investigations. Water depth, season, and fishing region were the best predictors to explain bycatch events. The present data suggest that the northern Adriatic may be an important nursery area for several elasmobranchs. They also highlight the urgent need for a better understanding of the interactions between elasmobranchs and fisheries to develop and apply suitable, ad hoc management measures.

Elasmobranch species are the direct or accidental catch of fisheries and can have a commercial importance. In the Mediterranean Sea, a long-term period of overfishing brought several demersal elasmobranchs to be depleted and threatened by extinction, due to vulnerability related to their life history traits. In such exploited species, information on genetic diversity and connectivity is lacking and should be collected to identify management units. In this study, we focused on two threatened smooth-hound species, Mustelus Mustelus (Linnaeus, 1758) and M. punctulatus (Risso, 1827), whose abundance and distribution showed a decline at the Mediterranean regional level in the last century. Thanks to an opportunistic yet extensive sampling, we obtained the largest subregional collection of specimens for genetic analysis so far. In total, 86 and 214 specimens of M. mustelus and M. punctulatus were collected between 2016 and 2020 in the Adriatic Sea and the Strait of Sicily. We assessed the population genetic structure typing 17 microsatellites and sequencing part of the mitochondrial control region in both species. We observed a substantial nuclear and mitochondrial genetic structure when accounting for the geographical sampling area for both species. Our results indicate the presence of at least two genetic stocks for each of the two species: one in the Strait of Sicily and the other in the Adriatic Sea. This study provides valuable data that should be integrated into a broader approach to define management units, improving the development of an effective management strategy for these threatened species in the Central Mediterranean Sea.