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The dietary composition and nutritional alteration resulting from time and size of thornback ray, Raja clavata, were investigated in the present research. For this purpose, the individuals were obtained from the commercial bottom trawl vessels operated around Gokceada Island, North Aegean Sea, Turkey between February 2019 and February 2020. The female:male ratio was found to be 1:0.79. The vacuity index was calculated for males, females and both individuals to be 5.8%, 4.7%, and 5.3%, respectively. The major food item groups were determined to be decapod crustaceans, teleost fish, and cepholopoda with IRI% (Index of Relative Importance) values of 77.72, 7.05, and 0.25, respectively. The best-represented food item was found to be Goneplax rhomboides. The prey types, abundance, and biodiversity were observed to change with the increasing lengths of R. clavata. The trophic level (TLw) of R. clavata was calculated to be 3.27, and it was observed that the TLw values were increased with the increasing individual length. The diet overlap was found to range from 40 to 49 cm and 50 to 59 cm TL in autumn and winter. The highest prey biodiversity was found in the length group of 70-85 cm TL and during spring. This study presents detailed findings on the feeding behaviour of R. clavata. In the future, food competition between the species should be monitored to develop a better understanding of the diet overlap. Thus, more comparisons should be conducted between the studies performed in varied geographical areas.

The effect of azide, fluoride, orthovanadate and EDTA sodium salts on the ecto-ATPase activity in erythrocytes of a scorpionfish (Scorpaena porcus L.) and thornback ray (Raja clavata L.) was studied. It was shown that under the influence of millimolar (mM) concentrations of the selected biochemical agents, significant differences in the hydrolytic activity of erythrocyte plasma membrane ecto-ATPases were revealed in cartilaginous vs. teleost fish. For example, thronback ray erythrocyte ecto-ATPase was practically insensitive to sodium azide. In contrast, scorpionfish erythrocyte ecto-ATPase was sensitive to sodium azide, which blocked the enzyme activity by 65% at a concentration of 20 mM. Thornback ray erythrocyte ecto-ATPase retained a significant activity (37%) at high (60 mM) concentrations of sodium fluoride, while scorpionfish erythrocyte ecto-ATPase was almost completely blocked at this concentration. EDTA acted as a modifier of thornback ray ecto-ATPase activity: at concentrations of up to 6 mM, ATP hydrolysis was actively blocked (by 58%), and at higher concentrations, ecto-ATPase activity was stimulated (up to 20%). An increase in the EDTA concentration (up to 12 mM) in suspensions of scorpionfish erythrocytes constantly stimulated the inhibitory effect of the chelator (up to 52% vs. control). The activity of ecto-ATPases in erythrocyts of the studied fish species was weakly blocked by sodium orthovanadate. These differences may reflect a higher tolerance of thornback ray erythrocyte ecto-ATPase to the effect of the above chemical reagents compared to a scorpionfish. The absence of the sodium azide inhibitory effect on thornback ray erythrocyte ecto-ATPase suggests that this ecto-ATPase may be referred to a family of type 2 ecto-NTPDases (ENTPD2), while scorpionfish ecto-ATPase may belong to type 1 ecto-NTPDases (ENTPD1).

A free-swimming thornback ray Raja clavata specimen demonstrating significant morphological abnormality is reported, captured by beam trawl in the Irish Sea off north Wales, UK. The anterior sections of both pectoral fins were separated from the head section for a length of approximately 140 mm extending from the rostrum tip to a point posterior of the spiracles, along with abnormal morphology of the gill slits. This phenomenon has been observed elsewhere but is the first documented example of this abnormality in the eastern Irish Sea, despite widespread targeting of the species across the region by commercial and recreational fishers. Possible causes and consequences of the observed abnormality are discussed.

The study deals with aspects of the population dynamics in the thornback ray (Raja clavata L., 1758), one of the most abundant cartilaginous fish caught in the North Aegean Sea. Females accounted for 73.08% and males 26.92% of all individuals. Total length of females and males ranged between 50.2 and 89.9 cm (disc width: 33.4–62.0 cm), and between 43.1 cm and 82.7 cm (disc width: 30.7–64.2 cm), respectively. Relationships between total length (TL) and total weight (TW), and between disc width (DW) and total weight (TW) were described by the equations: TW = 0.0041 TL3.10 and TW = 0.0178 DW3.03, respectively. Age data derived from vertebrae readings were used to estimate growth parameters using the von Bertalanffy function: L∞ = 101.71 cm, K = 0.18 y−1, t0 = −0.07 y for males and L∞ = 106.54 cm, K = 0.16 y−1, t0 = −0.28 y for females. The maximum age was 8 years for males and females. Total length at first maturity of males and females was 70.9 cm and 81.2 cm, respectively. Based on the gonadosomatic index and gonadal macroscopic observations, it was determined that the spawning period lasted throughout the year. Stomach content analysis showed that crustaceans (53.03% IRI) and teleosts (14.70% IRI) were the most preferred prey.

We studied the glycogen content in erythrocytes of two Black Sea cartilaginous fishes (Raja clavata, Dasyatis pastinaca) and four teleost species (Trachurus mediterraneus ponticus, Spicara flexuosa, Diplodus annularis, Scorpaena porcus). Glycogen accumulation in erythrocytes of teleost fish was about twice as high as in the ray fishes. Due to the unique ability of thornback ray R. clavata erythrocytes to well preserve their cell integrity in vitro in the cold (4°C), the dynamics of glycogen expenditure in erythrocytes was tracked over 11 days of storage until cell disintegration. Erythrocytes spent glycogen economically: during the entire storage period, only 52% of glycogen were spent. In the black scorpionfish S. porcus, erythrocytes were far less tolerant to being stored in the cold. The stability period of S. porcus erythrocytes suspended in physiological saline did not exceed two days. During this period, no significant changes in the glycogen concentration were observed.

The effect of azide, fluoride, orthovanadate and EDTA sodium salts on the ecto-ATPase activity in red blood cells (RBCs) of a scorpionfish (Scorpaena porcus L.) and thornback ray (Raja clavata L.) was studied. It was shown that under the influence of millimolar (mM) concentrations of the selected biochemical agents, significant differences in the hydrolytic activity of RBC plasma membrane ecto-ATPases were revealed in cartilaginous vs. teleost fish. For example, thronback ray RBC ecto-ATPase was practically insensitive to sodium azide. In contrast, scorpionfish RBC ecto-ATPase was sensitive to sodium azide, which blocked the enzyme activity by 65% at a concentration of 20 mM. Thornback ray RBC ecto-ATPase retained a significant activity (37%) at high (60 mM) concentrations of sodium fluoride, while scorpionfish RBC ecto-ATPase was almost completely blocked at this concentration. EDTA acted as a modifier of thornback ray ecto-ATPase activity: at concentrations of up to 6 mM, ATP hydrolysis was actively blocked (by 58%), and at higher concentrations, ecto-ATPase activity was stimulated (up to 20%). An increase in the EDTA concentration (up to 12 mM) in suspensions of scorpionfish RBCs constantly stimulated the inhibitory effect of the chelator (up to 52% vs. control). The activity of ecto-ATPases in RBCs of the studied fish species was weakly blocked by sodium orthovanadate. These differences may reflect a higher tolerance of thornback ray RBC ecto-ATPase to the effect of the above chemical reagents compared to a scorpionfish. The absence of the sodium azide inhibitory effect on thornback ray RBC ecto-ATPase suggests that this ecto-ATPase may be referred to a family of type 2 ecto-NTPDases (ENTPD2), while scorpionfish ecto-ATPase may belong to type 1 ecto-NTPDases (ENTPD1).

To describe the spawning period, size at maturity (Lm), reproductive load (Lm/Lmax), length at maximum yield per recruit (Lopt) of thornback ray (Raja clavata); and to assess the differences in these parameters from other populations, a total of 18 months samplings were conducted between February 2011 and December 2013 in the southeast Black Sea. A total of 265 (160 females and 105 males) specimens of thornback ray were examined. The mean total length (L) of females was significantly greater than the mean total length of males (p

Biochemical properties and some kinetic characteristics of whole-erythrocyte ecto-ATPase (EC 3.6.1.5) were studied in the Black Sea thornback ray Raja clavata L. It was shown that enzyme activity varied from 1.5 to 3.5 nmol Pi/min/μL of packed cells and peaked in the presence of 3.0-6.0 mM Mg2+. Ecto-ATPase exhibited broad substrate specificity towards splitting nucleoside triphosphates. The enzyme was tolerant to changes in ambient pH and exhibited maximum activity in the pH range from 5.5 to 7.7. The enzyme also showed high substrate affinity, with the Michaelis constant (KM) found to be 12.0 ± 1.0 μM and Vmax being 2.35 0.2 nmol Pi/ min/μL of packed cells. Erythrocyte ecto-ATPase in R. clavata was sustainable to erythrocyte storage at 4°C for four days and exhibited a tolerance to high concentrations of urea.

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.

Elasmobranchs are globally recognized as vulnerable due to their life-history characteristics, fishing pressure, and habitat degradation. Among the skates and rays caught by commercial fisheries, the thornback ray Raja clavata is one of the most economically important in Northwest European seas. However, the scarcity of biological knowledge about this species in Azorean waters has limited the stock assessment types that can be conducted. To improve information on its habitat preferences, spatial distribution and movement pattern, growth, sex ratio, mortality, and reproduction, as well as to investigate long-term changes in abundance and size, this study analyzed approximately 25 years of fishery-dependent and independent data from the Azores. Raja clavata was mainly caught at depths up to 250 m. Most of the tagged fish were recaptured near the release point. A larger–deeper trend was found, and females were larger and more abundant than males. Life-history parameters showed that R. clavata has a long lifespan, large size, slow growth, and low natural mortality. The sustainability of its population is of concern to fisheries management and, while our findings suggested a relatively healthy stock in the Azores, a thorough increase in data quality is required to better understand the stock condition and prevent overexploitation.

Despite increased focus on ascertaining the status of elasmobranch fish, the stock units for many species are uncertain. Data from mark-recapture tagging studies undertaken from 1959–2017 were analysed for 13 batoid species. Data were most comprehensive for skates (Rajidae), with 22,374 released and 3342 (14.9%) returned. Most data related to thornback ray Raja clavata, blonde ray R. brachyura and spotted ray R. montagui. Tags were generally returned from areas less than 50 km from their release, and usually from the ICES Division in which they were released. However, straight-line distances travelled of up to 910 km (R. brachyura) and 772 km (R. clavata) were recorded, highlighting that individual skates are capable of longer-distance movements. The maximum time at liberty was 16.6 years (R. clavata). Whilst mark-recapture data indicated that the current stock units used by ICES are broadly appropriate, southward movements of several skate species tagged off Northern Ireland (Division 6.a) to the Irish Sea (Division 7.a) were observed. In contrast, skates tagged in the Irish Sea and Bristol Channel (Division 7.f) generally remained in that area, with only occasional recaptures from Division 6.a.

By means of electronic microscopy, the structural distinctions of epithelial cells are revealed in three species of cartilaginous fish differing in their foraging: spiny dogfish Squalus acanthias (a typical fish predator), common stingray Dasyatis pastinaca, and thornback ray Raja clavata (benthos eaters-facultative fish predators). In the spiny dogfish, the length of microvillu in the brush border of enterocytes in the medial region of the spiral intestine is smaller than in Dasyatis pastinaca and Raja clavata (0.66 ± 0.05 vs. 1.16 ± 0.07 and 1.04 ± 0.10 μm) and their diameter, on the contrary, is greater (0.10 vs. 0.08 and 0.07 μm). In Dasyatis pastinaca, there is a well-developed glycocalix and the distal decrease of microvilli length. The role of the brush border enetocytes in the increase of digestive and transport surface of the intestine, as well as the role of particular organelles in digestions and transport of nutrients in the investigated fish, is discussed.

Raja clavata is the most widespread and landed skate species in the Mediterranean Basin. Despite its diffusion and economic importance, several aspects of its life history, such as age and growth, are poorly understood. This study evaluated the species’ growth in the South Adriatic Sea (Central Mediterranean Sea) and for the first time attempted an age validation through a tagging experiment. Thin sectioning of vertebral centra proved to be a more accurate preparation method in terms of age estimation precision and reproducibility than whole vertebral centrum staining (cobalt nitrate and ammonium sulfide technique). Marginal analysis showed a clear seasonal pattern, confirming the hypothesis of a single annulus deposition per year. A total of 291 vertebral centra were sampled and used for age estimation purposes. The oldest female was estimated to be 12 years old [total length (TL) = 89 cm], while the oldest male was aged 8 years (TL = 79.9 cm). Females were also found to be characterized by a slightly wider longevity range (ωL = 11.5, ωU = 16.8 years) than males (ωL = 7.8, ωU = 11.2 years). The von Bertalanffy growth curve fit the age and length data more accurately than the Gompertz and logistic models. Eighty-three thornback rays were tagged and released, of which two were recaptured. In both recaptured specimens, oxytetracycline marks were clearly visible. The band deposition after oxytetracycline injection and growth during the freedom period (about 1 year) were consistent with the age estimation method and criteria used and with the obtained growth results. Thus, the analysis of the vertebral centra extracted from the two recaptured specimens confirmed the hypothesis of the deposition of a single annulus per year and in general the age estimation criteria used in this study.

In this study, hot smoking process was applied to thornback ray (Raja clavata), which is a non-target catch, and the product obtained was vacuum packaged and then stored at refrigerated conditions (4±1 °C) for 120 days. The nutritional, chemical, microbiological, and sensory changes in the products were examined every 15 days. After the hot smoking process applied to thornback rays, significant changes were observed in the nutritional composition of the products (P

International audience; Elasmobranchs are k-strategy species with low reproduction rate and slow growth lending to increased anthropogenic vulnerability. Specific management measures to improve the conservation of elasmobranchs can be problematic due to insufficient information on their biology and ecology. Here, three sympatric skates occupying north-eastern Atlantic waters, which have differing conservation status were studied within ICES divisions 4.c, 7.d–e, 7.f–h and 8a–b and d. Fisheries-dependent data on skate bycatch and a series of environmental variables were used to model spatio-temporal differences in habitat use between the three species.Raja undulata, the undulate ray (IUCN red listed as ‘Endangered’) was observed to have a coastal distribution within the English Channel and the Bay of Biscay (ICES division 7.d–e and 8.a–b). Raja clavata, the thornback ray (‘Near threatened’), had a broader distribution with higher presence in the eastern English Channel and the southern North Sea (ICES division 7.e and 4.c). Raja montagui, the spotted ray’s probability of presence (‘Least concerned’) was higher off the coast of southern Ireland (ICES division 7.g). Seasonal and life-history trait differences were also observed.From the fisheries-dependent data, wider skate distributions than previously studied were modelled. Although the species do co-occur, spatio-temporal differences between these species were observed. This study contributes to a greater understanding of skate habitat during their different life history stages, and indicates reasons for R. undulata’s increased vulnerability than R. clavata and R. montagui. Information from the distribution models could be used for specific spatio-temporal management measures. Better understanding of the distribution of species can also help reduce bycatch of protected species such as R. undulata.

Dutch demersal fisheries in the North Sea is a mixed fishery that mainly targets Dover sole (Solea solea) with plaice (Pleuronectes platessa), turbot (Scophthalmus maximus), brill (Scophthalmus rhombus) and other species as valuable bycatches. The fleet currently uses two gear types: pulse beam trawls and conventional tickler chain beam trawls. Pulse beam trawlers operate with a temporary exemption from the EU prohibition to use electric stimulation in fishing gears, of which the last exemptions will expire in June 2021.To assess the consequences of transitions between pulse and tickler chain beam trawling for discards mortality, knowledge on the discards survival probabilities as well as the amount of discards is required for both gear types. The objective of the current study was to estimate discards survival probabilities for undersized plaice, sole, turbot, brill and thornback ray discarded by tickler chain beam trawl fisheries using fish condition as a proxy for survival probability. To this end the condition and reflex impairment of undersized fish in the catches of tickler chain beam trawlers were assessed and compared to similar data collected from pulse trawl fisheries. For spotted ray we assessed fish condition in tickler chain beam trawling but could not estimate its discards survival probability because a relation between survival probability and fish condition is lacking for this species. In this study direct mortality imposed by the tickler chain beam trawling ranged between 10 and 32% in flatfish species and was between 2-4 times higher than in pulse beam trawling. Direct mortality in ray species was lowest among the investigated species (2-8%) and did not differ between the two gear types. Differences in direct mortality were reflected in the condition scores. Direct mortality of sole was higher in tickler chain beam trawling (17%) than in pulse beam trawling (8%). Brill, turbot and plaice discarded by pulse beam trawling are in better condition than when discarded by tickler chain beam trawl fisheries. For sole no effect of gear type on fish condition could be detected. We consider the lower fish condition scores of brill, plaice and turbot from tickler chain beam trawling a direct reflection of the higher mechanical impact of this gear on the fish. For thornback ray and spotted ray no effect of gear type on fish condition could be detected. The predicted survival of plaice, brill and turbot discards indicate that discards survival could indeed be lower in tickler chain beam trawl fisheries compared to pulse beam trawl fisheries. For sole and thornback ray discards we found no evidence for such difference between gear types. The discards survival probabilities for tickler chain beam trawling as presented in this study should be considered as predictions based on the currently best available information instead of definite values. Actual measurements of discards survival at sea are needed to confirm and quantify survival probabilities in tickler chain beam trawling.

The verification of food authenticity and provenance is a complex task and has raised public concern in recent years due to multiple episodes of food fraud and potential risks to consumers. In this sense, the evaluation of multi-elemental signatures is increasingly applied to confirm and validate the site of origin of animal products. Yet, we lack understanding of its efficacy for mobile organisms such as fish. Using multi-element Total Reflection X-ray Fluorescence (TXRF) analysis of muscle of thornback ray Raja clavata we successfully identified the fishing area of individuals collected in four areas along the Portuguese Atlantic coast (Atlantic Iberian waters, Northeast Atlantic). Overall, As, Fe, Sn, V and Zn presented higher contributions to discrimination (especially Fe and Rb for neighbouring collection areas), whilst the higher concentration elements (Na, K, P, S, Ca, Cl, Br and Sr) had similar concentrations among locations. Rays captured in the two areas with higher urbanization/industrialization presented higher concentration of elements associated with anthropogenic activities (such as As, Zn, Sn and V). In terms of food safety, only 0.9% and 2.8% of the individuals surpassed the recommended thresholds values for human consumption for Hg and Cd respectively. A canonical analysis of principal components resulted in classification accuracy of thornback ray to collection site of 56.7–84.2% (depending on site), with an overall accuracy of 65.1% over c. 500 km of coast in the Northeast Atlantic.

The lack of information on age validation often affects ageing studies in cartilaginous fish, even in the most common species. Recently, the annual growth band deposition pattern has been directly validated for thornback ray in the Mediterranean Basin, thus providing a highly reliable protocol for age reading. In this regard, taking advantage of this new information, the present study aims to investigate this species growth for the first time over a wide area of the Western and Central Mediterranean Sea, involving four different FAO geographic sub-areas. In order to provide an accurate description of the species growth, different models were fitted to the age-length data obtained from the observation of vertebral centra thin sections. A total of 720 specimens were analysed (358 females and 362 males) with total length ranging between 11.5 and 86.4 cm. The corrected Akaike's Information criterion (AICc) indicated, among the tested models, the three-parameter von Bertalanffy function as the most robust in describing the species growth. Growth modelling outcomes revealed the thornback rays as capable of growing relatively fast during the first years; the growth rate gradually slows down allowing maximum sizes of about 90–100 cm in total length to be reached. Significant discrepancies in the growth pattern were found between sexes in all investigated areas with the only exception being in the Northern Tyrrhenian Sea. Differences in growth patterns were observed between areas, specifically in the estimated growth rate of the species for each sub-region. The present study, confirmed the importance of the availability of a validated ageing protocol and testing multiple growth models. Moreover, our results highlighted the urgent need to investigate a species growth in a wide geographic area, searching also for possible differences at sub-region level. Providing this information could indeed allow eventual management plans to be adapted to the exact growth pattern that the species exhibit in the region, in this way increasing their effectiveness.

The interactions between selenium (Se) and mercury (Hg) were assessed in order to interpret public health risk, associated with dietary mercury exposure due to fish consumption. For this purpose, the mass and molar concentrations of Se and Hg were determined in the edible tissues of six species of fish, collected from the commercial fishing grounds of Turkey. The Se/Hg molar ratios and selenium health benefit values (Se-HBVs) were also calculated. The main fish species exported from Turkey to Europe were studied to determine the risks or benefits for human health. The mean Hg levels (μg g−1, wet weight) ranged from 0.01 (in turbot) to 0.45 (in Atlantic bluefin tuna). The average selenium concentrations were between 0.96 μg g−1 (in thornback ray) and 1.86 μg g−1 (in turbot). The molar ratios of Se/Hg were above 1 for all species and greater than 100 in turbot, red mullet, and whiting. Positive Se-HBVs were determined for all samples, showing health benefits. Since Se is present in molar excess of Hg in the fish muscles, organic Hg exposures from eating these fish is not a public health concern.

The first good evidence of the role of intensive commercial fishing in the decline and possible extinction of a marine parasite is presented. The larva of Stichocotyle nephropis Cunningham, 1887 (Aspidogastrea: Digenea) was described in 1887 from the outside of the intestine of the decapod crustacean Nephrops norvegicus (L., 1758) in the North Sea. Similar larvae were found outside the intestine of the American lobster Homarus americanus (Milne-Edwards, 1837) caught off New England in 1895. The adult form was first found in 1898 in the bile ducts of the thornback ray Raja clavata (L., 1758) from the North Sea, then in the barndoor skate Dipturus laevis (Mitchill, 1818) caught off Nantucket. There have been few records of its occurrence since then, with the last records from the northeast and northwest Atlantic published in 1972 and 1986 respectively, despite the recent attempts reported herein to find larvae and adult parasites. Both the elasmobranch final hosts are listed as “near threatened” or “ endangered” and the latest evidence on their population sizes suggests that they may have been fished to below the thresholds required for successful transmission of the parasite.

The implementation of spatial protection measures is currently a priority in batoid species' conservation strategies, but their spatial ecology remains largely unknown. We provide some preliminary insights into the movement patterns of the white skate (Rostroraja alba), a batoid classified as Critically Endangered in European waters. Three individuals (two females: one mature, one immature and one immature male) were monitored with acoustic telemetry in a marine protected area (Portugal). The mature female remained present in the study area throughout the whole monitoring period (20 months). Residency analyses revealed this specimen spent more than 70% of the time within this coastal marine park. The immature female and the immature male were only detected during three and four months, respectively. Whether the uncovered movement patterns are common within the population remains unclear, but the present study provides useful information to better plan future research on the movement ecology of a rather unstudied species. Fundacao para a Ciencia e a TecnologiaPortuguese Foundation for Science and Technology [CCMAR/Multi/04326/2013] LIFE-BIOMARES project [LIFE06 NAT/P/000192] Project Buffer ERA-Net BiodivERsA [ANR-12-EBID-0006] CCMAR - Centre of Marine Sciences [CCMAR/BI/0004/2018]

We have evaluated the fatty acid composition of the livers from two cartilaginous fish species Raja clavata (thornback ray) and Mustelus mustelus (common smooth-hound) caught off the Northern Aegean Sea. While there was generally little variation between species, Mustelus mustelus indicated low saturated (SFA) in summer (29.61%), in spring (32.57%), in autumn (30.07%) and in winter (31.81%) and high polyunsaturated fatty acid (PUFA) in summer (40.35%), in spring (36.50%), in autumn (30.21%) and in winter (27.26%) levels. The dominant fatty acids were palmitic acid (C16:0), oleic acid (C18:1 (n-9)), eicosapentaenoic acid (EPA; C20:5 (n-3)), and docosahexaenoic acid (DHA; C22:6 (n-3)) in both cartilaginous fish species in all seasons. The ratio of DHA/EPA with respect to the total of fatty acids in livers oils was ranged from 2.66% to 4.44% for Mustelus mustelus and 2.89% to 4.46% for Raja clavata . The n:3/n:6 ratio of thornback ray was higher compared to smooth-hound shark in all seasons. The liver oil of R. clavata and M. mustelus represent a valuable source of omega-3 PUFA that can be used for human and animal nutrition.

In the Northeast Atlantic, elasmobranchs are a common bycatch in many fisheries, including demersal trawls, longlines, or gillnets and many countries do not have regulations or any control over the amount taken. In the Mid Atlantic, the Azores EEZ (Exclusive Economic Zone), small-scale fishing operations, artisanal and hook-and-line fishing methods are responsible for part of local total landed elasmobranch biomass, although some species are specifically focused and severely harvested by international large-scale fleets. This work provides a review and analysis of the commercial elasmobranch fisheries in the Azores EEZ, and its evolution over the last two decades, highlighting management priorities, taking into account the Northeast Atlantic elasmobranch fisheries status. In the Mid-Atlantic, elasmobranch fisheries mainly target 4 species, that are usually landed as bycatch: the tope shark ( Galeorhinus galeus ) and the thornback ray ( Raja clavata ), captured mainly by local demersal artisanal fisheries, the blue shark ( Prionace glauca ) and the shortfin mako shark ( Isurus oxyrinchus ) captured by a more industrialised fleet, including those from foreign nations. Considering elasmobranchs life history traits and fishery history, caution is advised in the development of a management strategy focusing on these species, considering the Northeast Atlantic context and regional, local and national interests.

There are few studies investigating captive conditions for commonly kept public aquaria species. Here the thornback ray (Raja clavata) was used to determine preferred captive conditions via choice tests and behavioural observations. Substrate type, substrate colour, substrate depth, group size and refuge use were all used to assess usage, number of stereotypic behaviours and activity in captive born rays. Sand was the preferred choice of substrate which also brought fewer surface breaking behaviours (a possible stereotypic behaviour) compared to gravel or bare tanks. Lighter colours of sand were preferred, as were deeper depths whilst increasing group size increased possible stereotypic behaviours. Type of resting behaviour (horizontal vs vertical) also differed within experiments − rays switched from horizontal to vertical resting, on the side of the tank when using gravelled versus sandy areas of the tank. The rays in this study appeared not to use refuges. Very few published studies have focused on what aquatic animals want, here we use preference tests, which are a useful way of determining what the animal wants, and can help aquarists provide the best conditions for captive thornback rays.

Angiotensin I-converting enzyme (ACE) inhibitory peptides have been searched in thornback ray (Raja clavata) muscle hydrolysed with Bacillus subtilis A26 proteases until a hydrolysis degree of 18.35%. The hydrolysate showed an IC50 of 0.83 mg mL−1. To identify peptides responsible for this activity, the extract was eluted through size-exclusion chromatography and fractions collected. The highest ACE inhibitory activity was found for fractions F2 and F3 which had IC50 of 0.42 and 0.51 mg mL−1, respectively. These fractions were analysed by nano-liquid chromatography coupled to tandem mass spectrometry (nLC-MS/MS). A total of 131 and 108 peptide sequences mainly derived from actin, myosin heavy chain and procollagen alpha 1 chain proteins were identified in fractions F2 and F3, respectively. FQPSF and LKYPI showed the best results with an IC50 of 12.56 and 27.07 μM, respectively. These results prove the potential of thornback ray muscle hydrolysate as a source of ACE inhibitory peptides., This work was funded by a grant from the Ministry of Higher Education and Scientific Research of Tunisia and grant Prometeo/2012/001 from Conselleria d´Educació Cultura i Sport of Generalitat Valenciana, both are acknowledged. JAEDOC- CSIC postdoctoral contract cofounded by ESF to L.M. is also acknowledged

1st International Fisheries Symposium, WOS: 000380019500034, The study objective was to investigate the profiles of tocopherol, heavy metals, and fatty acids in the liver oil of female and male thornback ray Raja clavata from the Black and Mediterranean seas. The fish liver oil analyses were carried out by using a spectrophotometer (Hitachi U-1900), ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry, and a GC-MS (gas chromatography-mass spectrometry), respectively. Results showed that the tocopherol content differed between the sample origin and gender (range of 42.3-134.5 mg kg(-1)). Pb, Cd, and Mn contents in livers of all R. clavata were lower than for Cu, Fe, and Zn. Levels of 7.6 and 8.9% in the eicosapentaenoic acid (EPA) were found to be higher in Black Sea thornback rays than in Mediterranean specimens (4.5 and 5.8%) (P < 0.05). All thornback ray liver oils contained large amounts of docosahexaenoic acid (DHA) in the range of 19.9-26.1%., European Univ Lefke, Cyprus Marine Sci Fdn, World Sturgeon Conservat Soc, Prime Minist, Minist Foreign Affairs, Minst Agr, Turkish Republ No Cyprus, Nat Resources & Food