The first confirmed cases of full albinism in rajid species

Three albino skate specimens (Rajidae) were captured from the North Sea and English Channel between 2008 and 2011. Using DNA barcoding (COI gene) and morphometric analyses, species were identified as a spotted ray Raja montagui, a blonde ray Raja brachyura and a thornback ray Raja clavata. This finding represents the first record of full albinism (a lack of skin and retinal pigmentation) in rajid species.     

Length–weight relationships for nine species of batoids from the Iskenderun Bay,Turkey

Presented are length–weight relationships for Rhinobatos rhinobatos, Rhinobatos cemiculus, Gymnura altevela, Dasyatis pastinaca, Rhinoptera marginata, Pteromylaeus bovinus, Torpedo nobiliana, Raja miraletus and Raja clavata captured by gillnet, longline and bottom trawl fishing between May 2010 and July 2011 off the east coast of Iskenderun Bay, Turkey.     

Characterisation of polymorphic microsatellite markers for skates (Elasmobranchii: Rajidae) from expressed sequence tags

Simple sequence repeat markers (SSRs, microsatellites) were characterised for skates (Elasmobranchii: Rajidae) from published expressed sequence tags (ESTs) of Leucoraja erinacea. These were tested in four European species (Raja clavata, Raja montagui, Dipturus batis, and Leucoraja naevus). Thirteen of the fourteen amplified loci were polymorphic in at least one species. Polymorphic loci possessed on average 4.5–5.9 alleles per species, and expected heterozygosity ranged from 0.05 to 0.88. Possible null alleles were detected at three loci, while one locus showed significant deviation from Hardy–Weinberg Equilibrium proportions. Three locus-pairs exhibited significant linkage disequilibrium in one or more species. This marker set will be valuable for population genetic analyses of the focal taxa, and may prove useful for studies of other skate species.     

Molecular barcoding of skates (Chondrichthyes: Rajidae) from the southern Northeast Atlantic

Serra‐Pereira, B., Moura, T., Griffiths, A. M., Gordo, L. S. & Figueiredo, I. (2010). Molecular barcoding of skates (Chondrichthyes: Rajidae) from the southern Northeast Atlantic. —Zoologica Scripta, 40, 76–84. Due to their vulnerability to fishing pressure, many species of skate (Rajidae) in the Northeast Atlantic are undergoing declines in abundance. The assessment of stock status and subsequent proposal of management measures are often complicated by high levels of species diversity and endemism, coupled with morphological and ecological conservatism, which makes distinguishing between species difficult. To improve the identification of skates and investigate the phylogenetic position of endemic species the cytochrome c oxidase subunit I (COI) was sequenced in 12 species (Dipturus oxyrinchus, Leucoraja naevus, Leucoraja circularis, Neoraja iberica, Raja brachyura, Raja clavata, Raja maderensis, Raja microocellata, Raja miraletus, Raja montagui, Raja undulata, Rostroraja alba) inhabiting the Portuguese waters. Based on sequence divergence R. maderensis and R. clavata only differ by 1% of the 652 bp COI sequence, questioning the recognition of R. maderensis (considered to be endemic to Madeira and the Azores), as a reproductively isolated species. Otherwise, there was clear phylogenetic support for the different genera and all the remaining species, although the genetic divergence was low compared to other chordates. In particular, COI analysis allowed clear identification of the morphologically similar species R. brachyura and R. montagui.     

Diet composition of the Thornback Ray,Raja clavata Linnaeus, 1758 (Elasmobranchii: Rajidae) in the Turkish Aegean Sea

The diet of Raja clavata (Thornback Ray) was studied in 2008–2009 in S??ac?k Bay in the eastern Mediterranean, based on 187 stomach contents obtained by commercial trawl operations. 40 different prey species were found. Mysidacea, Parapenaeus longirostris and Plesionika sp. were the most abundant prey items. The results indicate that the main prey varies considerably depending on the ecological characteristics of the habitat.     

Reproductive biology of Raja clavata (Elasmobranchii: Rajidae) from Southern Black Sea coast around Turkey

Specimens of Raja clavata were monthly collected at the coast of Havaalan? (Trabzon/Turkey) from January 2009 to December 2009 at depths between 20 and 40?m. A total of 230 individuals of thornback ray (131 females and 99 males) were collected by bottom trawls during research cruises. Using logistic regression, it was determined that TL at 50% maturity of males was 718?mm TL and of females 746?mm TL. The ovarian fecundity ranged from 27 to 60 yellow follicles in both ovaries. Females carrying egg cases were found in July and October. Variations in the gonadosomatic and hepatosomatic indices indicated a continuous reproductive cycle during the year.     

Development of molecular and morphological markers to improve species-specific monitoring and systematics of Northeast Atlantic and Mediterranean skates (Rajiformes)

The Northeast Atlantic and Mediterranean skates (Rajidae) showed remarkable species diversity but with high morphological and ecological conservatism. Since skates are particularly vulnerable to the bottom trawl fishery, species-specific demographic surveys as well as studies defining life history and evolutionary traits are important in prioritising conservation programs. However, the identification of juveniles and adults of some species may be difficult using referenced guidelines and identification keys. Therefore, we attempt to develop markers for species identification through the parallel analysis of a 16S rDNA gene sequence and of several morphological characters on 135 individuals collected by trawl surveys in the Adriatic Sea and putatively assigned to six taxa. Species-specific haplotypes were defined for Raja miraletus, Raja montagui, Dipturus oxyrinchus, since a solid accordance between species boundaries and well-differentiated haplotypes was observed. Comparative analysis of 16S rDNA sequences allowed the identification of three juvenile specimens of Leucoraja circularis, a species that rarely occurs in the Adriatic Sea. On the contrary, morphological traits and haplotype distribution were largely discordant in Raja asterias and R. clavata. While all putative R. clavata individuals showed a unique haplotype (H-CLA), only 8 of 30 putative R. asterias individuals possessed a second weakly divergent haplotype (H-AST). The remaining 22 R. asterias carried the H-CLA. The multivariate analyses of morphometric and meristic characters in putative R. clavata and R. asterias revealed the clustering of individuals regardless of haplotypes. However, a bimodal distribution of R. asterias and R. clavata samples would suggest that two separated taxa might exist, both sharing the two 16S rDNA haplotypes. The haplotype distribution appeared to be significantly correlated only to the standardised disc length/total length (DL/TL) variation. Three alternative explanations may support this scenario: (i) an incomplete lineage sorting process in two morphologically yet distinct taxa; (ii) a recent hybridisation between the two taxa; (iii) the two taxa are morphologically plastic species and all considered morphological characters may be misleading in discriminating between them at all maturity stages, except for the DL/TL. However, further analyses on larger data sets and using molecular key markers (i.e. nuclear genes) will be needed to definitely resolve the status of these taxa. Molecular relationships among rajid taxa are largely consistent with systematics based on internal and external anatomical features. This multidisciplinary study contributed to defining the pattern of species diversity and abundance of rajids in the Adriatic Sea.     

Population ecology and juvenile density hotspots of thornback ray (Raja clavata) around the Shetland Islands,Scotland

Elasmobranchs are facing global decline, and so there is a pressing need for research into their populations to inform effective conservation and management strategies. Little information exists on the population ecology of skate species around the British Isles, presenting an important knowledge gap that this study aimed to reduce. The population ecology of thornback ray (Raja clavata) around the Shetland Islands, Scotland, was investigated in two habitats: inshore (50–150 m deep) and shallow coastal (20–50 m deep), from 2011 to 2022, and 2017 to 2022, respectively. Using trawl survey data from the annual Shetland Inshore Fish Survey, the size composition of R. clavata catches was compared between shallow and inshore habitats across 157 trawl sets, and 885 individuals, over the years 2017–2022. Catch per unit effort (CPUE) of R. clavata was significantly higher in shallow than that in inshore areas (ANOVA, F = 72.52, df = 1, 5, p < 0.001). Size composition also significantly differed between the two habitats (analysis of similarities, R = 0.96, p = 0.002), with R. clavata being smaller in shallow areas and juveniles (<60 cm) occurring more frequently. Spatial distribution maps confirmed density hotspots of juveniles in shallow habitats, with repeated use of certain locations consistent over time. The results of this study provide the first evidence for R. clavata using shallow areas for potential nurseries in Shetland, which can inform the IUCN's Important Shark and Ray Area process. Furthermore, this study provides important new population ecology information for R. clavata around Shetland, which may have important conservation implications and be valuable for informing species and fisheries stock assessments in this region.     

Ultrastructure of Elasmobranch and Teleost Erythrocytes

The ultrastructure of circulating erythrocytes of Raja clavata and Torpedo marmorata (Elasmobranchs) and Rutilus rutilus and Gobio gobio (Teleosts) was comparatively described in relation to their function. The existence of intranuclear hemoglobin and the degradation of cytoplasmic organelles are related to hemoglobin storage. Lysosome-like vesicles and microtubular marginal bands are also common elements of these cells. Thus, the presence of numerous cytoplasmic organelles in circulating erythrocytes suggests a certain immaturity, in relation to those in mammals.     

Length–weight relationships of 24 fish species from the North Aegean Sea, Turkey

Length–weight relationship parameters of the form W = aL^b are presented for 24 fish species from the North Aegean Sea: Scyliorhinus canicula, Mustelus mustelus, Squalus acanthias, Torpedo marmorata, Dipturus oxyrinchus, Raja clavata, R. miraletus, Dasyatis pastinaca, Gymnura altavela, Myliobatis aquila, Chimaera monstrosa, Conger conger, Argentina sphyraena, Chlorophthalmus agassizi, Caelorinchus caelorhincus, Gadiculus argenteus argenteus, Phycis blennoides, Hoplostethus mediterraneus, Capros aper, Macroramphosus scolopax, Helicolenus dactylopterus, Peristedion cataphractum, Lesueurigobius friesii and Lepidopus caudatus.     

Tocopherol,heavy metals (Cd,Pb, Cu,Fe, Mn,Zn), and fatty acid contents of thornback ray (Raja clavata Linnaeus, 1758) liver oil in relation to gender and origin in the Mediterranean and Black seas)

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%.     

Echinobothrium clavatum n. sp. (Cestoda,Diphyllidea) from the spiral valve of Raja clavata L., 1758, including a note on its ultrastructure and a key to species of the genus

Echinobothrium clavatum n. sp. from the spiral valve of the thornback ray Raja clavata from the Irish Sea is described and illustrated. On the basis of the number of apical hooks it resembles most closely E. musteli but can be distinguished from it by the absence of spines on the rostellum and the different number of spines on the cephalic peduncle. A generic diagnosis together with a key to species of the genus is given. Transmission and scanning electron microscopy of the scolex indicates that the tegument of the rostellum is capable of taking up food by pinocytosis.     

Morphological descriptions of the eggcases of skates (Rajidae) from the central-western Mediterranean,with notes on their distribution

Eggcases of eight rajiform skates (Dipturus nidarosiensis, D. oxyrinchus, Leucoraja melitensis, Raja asterias, R. brachyura, R. clavata, R. miraletus and R. polystigma) present in the central-western Mediterranean are described, based on specimens obtained from fishery surveys. Eggcase features such as dimensions, horns and apron lengths, and presence/absence of lateral keels were crucial to discriminate the eggcases of the various species. Morphological and morphometric data, confirmed by the multivariate analysis, indicated that the eggcase of R. miraletus and L. melitensis were distinct from those of the other species for being unkeeled. Within the species having keeled eggcases, those of the genus Dipturus and R. brachyura were discriminated from the remaining group by having the largest dimensions and aprons. Sandy bottoms (<100–150 m depth) were identified as egg-laying sites (i.e. sites with females bearing eggcases in uteri) for many species belonging to genus Raja Raja asterias, R. brachyura, R. miraletus and R. polystigma). The finding of R. asterias and R. miraletus carrying eggcases yearly on the same sites, seems to confirm the theory that many rajid species demonstrate site fidelity, returning to the same depositional area on an annual basis. Some remarks on reproductive biology of these skates are also provided. The eggcase identification key reported here represents the first for the Mediterranean and may be useful, in the future, to identify egg-laying grounds of skates with a nonlethal method.     

Ultrastructure of Elasmobranch and Teleost Thrombocytes

Zapata, A., Carrato, A. 1980. Ultrastructure of elasmobranch and teleost thrombocytes. (Departamento de Morfología Microscópica, Facultad de Biología, Universidad Complutense, Madrid, Spain.) — Acta zool. (Stockh.) 61 (3): 179–182. The ultrastructure of circulating thrombocytes of Raja clavata and Torpedo marmorata (Elasmobranchs) and Rutilus rutilus and Gobio gobio (Teleosts) was described. In elasmobranchs, only one thrombocytic cell type was found, while teleosts presented two types. These cells contained microtubules and cytoplasmic granules, whose functional significance related to clotting processes is analyzed.     

Ultrastructure of Spermiogenesis in Acanthocotyle and Myxinidocotyle (Platyhelminthes,Monogenea, Acanthocotylidae)

Abstract Spermiogenesis was studied by transmission electron microscopy in the acanthocotylid monogeneans Myxinidocotyle californica (from Eptatretus stoutii) and Acanthocotyle lobianchi (from Raja clavata). In Myxinidocotyle and Acanthocotyle, the zone of differentiation shows two 9+‘1’ axonemes, the elongating nucleus and mitochondrion, and a single cortical cytoplasmic microtubule. This single microtubule is found in the mature spermatozoon of both species and was also noted in capsalids. This requires a modified definition of ‘pattern 2’ of spermatozoa which becomes: ‘spermatozoa with two axonemes and no cortical microtubules, except one single element much shorter than the spermatozoon’. A very unusual structure was found in Myxinidocotyle, but not in Acanthocotyle: the centriolar derivative of one of the 9+‘1’ axonemes is made up of 18 diverging singlets of unequal length associated with electron-dense cytoplasm. This seems to be the first case of a centriolar derivative without nine-fold symmetry associated with an axoneme with nine-fold symmetry.     

Splenic Erythropoiesis and Thrombopoiesis in Elasmobranchs: An Ultrastructural Study

Zapata, A. 1980. Splenic erythropoiesis and thrombopoiesis in elasmobranchs: an ultrastructural study. (Department of Anatomy, School of Medicine, University of California, Los Angeles, U.S.A.) — Acta zool. (Stockh.) 61(1): 59–64. Erythropoiesis and thrombopoiesis occured in splenic red pulp of Raja clavata and Torpedo marmorata (Elasmobranchs, Batoidea). Both processes are intravascular and later developmental stages of erythrocytes can be also found in peripheral blood. Stages of erythropoiesis showed a successive increase of nuclear condensed chromatin and cytoplasmic hemoglobin content. Aspects of cytoplasmic granules suggested the existence of two thrombocytic precursors in these elasmobranchs. The importance of hemopoietic microenvironments for blood formation is emphasized in this work.     

Characterization and isolation of DNA microsatellite primers in Raja clavata L. (thornback ray,Rajidae)

The thornback ray, Raja clavata, is an elasmobranch (cartilaginous fish). Since the 1950s, its stock has severely declined. In order to investigate the genetic population structure of the species, we developed microsatellite loci. The five loci reported here have eight to 48 alleles per locus and display an observed heterozygosity ranging from 0.32 to 0.98 with no deviation from the Hardy–Weinberg equilibrium. In the test panel of 122 individuals from three populations, no null alleles, band‐stuttering, large allele dropouts or linkage disequilibrium was detected.     

Size-related mating and mate guarding in the orb-web spiderNephila clavata (Araneae,Araneidae)

The orb-web spiderNephila clavata satisfies three conditions for assortative mating proposed by Ridley (The Explanation of Organic Diversity. The Comparative Method and Adaptations for Mating, Clarendon, Oxford, 1983); (1) a large male advantage in male-male competition, (2) a correlation between female size and fecundity, and (3) a long pairing duration. To test Ridley's hypothesis, size assortative mating and guarding were examined in the field. When data were pooled over time, assortative mating was found but this was due to temporal covariation of body sizes of males and receptive females. After controlling for the effect of time, size assortative guarding was not detected, although females guarded by males were larger than those not guarded in the early breeding season. Possible reasons for the absence of size assortative guarding were discussed.     

Elasmobranch species richness,fisheries, abundance and size composition in the Azores archipelago (NE Atlantic)

ABSTRACT

Elasmobranchs are a vulnerable resource, more susceptible to overfishing than most teleosts, and their assessment is complicated due to a general lack of information about their fisheries, biology and ecology. This study aimed to analyse all fishery and survey data available for elasmobranchs caught over the past c. 25 years around the Azores (NE Atlantic) to provide a baseline information, which can be used to inform stock assessment and management strategies. Elasmobranch species covered pelagic, benthopelagic and demersal habitats, from shallow to deep-water strata in areas around the islands and seamounts. These species are taken accidentally as by-catch of three main fisheries: swordfish fishery, black scabbardfish fishery and demersal bottom longline fishery. The latter represents one of the most important fishing activities in the Azores, and frequent elasmobranch by-catches include Raja clavata, Galeorhinus galeus, Deania calcea, D. profundorum, Etmopterus pusillus and E. spinax. A slight reduction in the abundance indices of these species was observed, despite the implemented technical measures (e.g. minimum size, zero catch). Little is known about resource dynamics for the Azorean region and no analytical assessments have been conducted. This study highlights the vulnerability to overfishing of these resources and the urgent need to develop management strategies.     

Decreased reproductive rate of the spider,Nephila clavata,inhabiting small woodlands in urban areas

The reproductive characteristics and feeding conditions of the spider,Nephila clavata, were examined at some urban and non-urban woodland sites. More than 80% of females were gravid by late October in both non-urban and large urban woodlands, whereas only 10%–30% were gravid in small urban woodlands. The expected number of eggs per female in mid-October was also lower in the small urban woodlands, although body length was not reduced. This suggests that reproductive failure was not caused by food shortage during the nymphal stage. Relative food consumption rate, prey size, biomass and size of potential prey during the adult stage all tended to be lower in small urban woodlands. These results suggest that decreased reproduction ofN. clavata in small urban woodlands is caused by food shortage during the adult stage, particularly a shortage of large insects.