Raja Radula Research Articles

High bycatch rate of the coral Cladocora caespitosa offsets the low discards ratio in Thermaikos Gulf gillnet fishery

While hanging nets may have fewer overall environmental impacts than towed gears, they still catch unwanted species and sizes, which are then discarded. Gillnets are one of the most common types of nets used in Mediterranean small-scale fisheries, with commercial catches and discards containing a diverse range of fish and invertebrate species. In this study, the catch profile of gillnets in the Thermaikos Gulf (NE Mediterranean) was analyzed with a focus on the discarding of species with unfavorable conservation status, such as the Mediterranean-endemic scleractinian coral Cladocora caespitosa, which is listed as endangered due to declining population sizes. Our survey was conducted over two seasons (May to October in 2020 and 2021) and included 69 fishing trials under realistic fishing conditions. In general, gillnets exhibited a relatively low discards ratio (17.2%; 7.1% when only fish were considered) and a low prevalence and capture intensity of endangered or threatened species; during the entire survey, only one chondrichthyan was captured (1 specimen of Raja radula), while only two out of 54 fish species were of vulnerable IUCN status. These advantages were offset in part by the high catchability of C. caespitosa colonies, which occurred in 61% of hauls and accounted for 53% of total invertebrate biomass and 30% of total discarded biomass. The likelihood of hauling living colonies of C. caespitosa was higher when fishing over known coral beds (81% vs. 43%), and the overall probability of hauling C. caespitosa in any state was 18% higher over coral beds, suggesting that gillnets frequently detach colonies from the seafloor, which are then dispersed over a larger area as fragments with probably low survival potential. Our findings highlight the importance of identifying C. caespitosa beds so that fishermen avoid setting their nets in these areas, provided that they are well-informed and educated about the ecological significance of this endemic, threatened, and ecologically important species.

Myxidium tunisiensis n. sp. (Myxosporea: Myxidiidae) infecting the rough skate Raja radula Delaroche, 1908 (Rajiformes: Rajidae) from North East Tunisia.

A new marine myxosporean, Myxidium tunisiensis n. sp. (Myxosporea: Myxidiidae), is described infecting the gallbladder of the rough skate Raja radula Delaroche, 1908 (Chondrichthyes: Rajidae) harvested from the Bay of Bizerte, Tunisia. Observed stages of the parasite were floating free in the bile. Plasmodia, disporic or polysporic, contain disporic pansporoblasts measuring 23.0-27.2μm in maximum diameter and 21.0-25.5μm in minimum diameter. Mature myxospores, which are elongated, typically fusiform measured 18.6 ± 1.7 (17.2-22.0) μm in length, 8.6 ± 1.2 (7.2-11.2) μm in width and 8.2 ± 0.9 (6.4-10.1) in thickness. Myxospore valves are symmetrical with 9-10 longitudinal striations. Two polar capsules, pyriform, were equal in size, measuring 5.8 ± 0.4 (5.2-6.7) μm in length and 3.1 ± 0.2 (3.0-3.2) μm in width, with 5-6 polar filament turns. The infection was prevalent throughout the year with the highest prevalence in autumn (81.8%) and the lowest in winter (32.3%). The seasonal prevalence of M. tunisiensis n. sp. in the Bay of Bizerte appeared to fluctuate according to seawater temperature. The morphological and morphometrical differences with all Myxidium spp. described so far, complemented by molecular data, prove clearly that the present species is a new member of the genus Myxidium. The SSU rDNA phylogenetic analyses revealed that Myxidium tunisiensis n. sp. clustered within the oligochaete-gallbladder clade in a basal position to the marine subclade of Myxidium baueri and Myxidium coryphaenoideum. While the new species branching pattern is stable in the ML and the BI analyses, it changed in the MP analysis. This is the first molecular study of a Myxidium species infecting an elasmobranch host inhabiting the Mediterranean Sea.

Approaching the “real” state of elasmobranch fisheries and trade: A case study from the Mediterranean

Elasmobranchs are sensitive marine species due to their K-strategic life characteristics in combination with the intensification of fisheries. Despite the regulations and conventions protecting several species, elasmobranchs are still caught as bycatch and landed throughout the Mediterranean, a location where the pressure on shark populations is well documented. Severe knowledge gaps still exist regarding their biology, ecology and the exploitation by fisheries, due to limited research and the fact that in almost all Mediterranean countries, elasmobranchs are recorded by the national authorities in aggregated landing categories. To overcome such issues, we contrasted landings and trade of elasmobranchs using an integrative sampling in auction markets, landing sites, and fish markets at three important sites in Greece, combined with DNA analysis to address mislabeling. Five species contributed more than half of the total elasmobranch catches for all fisheries combined (62.5%); Scyliorhinus canicula (21.6%) and to a lesser extent Dasyatis sp., Mustelus mustelus, Raja radula and Dasyatis pastinaca (12.8%, 11.7%, 9.6%, and 6.9% respectively). Results highlighted that small-scale fisheries underreported catches of threatened elasmobranchs. About 50–60% of the elasmobranch landings were threatened species while in the fish markets the corresponding contribution was reduced to 26%. Mislabeling was common throughout the year with several species sold under different names for increasing profit or to hinder their protection status. The current practices do not satisfy Common Fisheries Policy in terms of treacability, and the fishing of threatened elasmobranchs raises additional concerns as a conservation priority.

Length-Weight Relationships of 31 Fish and Invertebrate Species in the Northern Aegean Sea (Eastern Mediterranean Sea)

The purpose of this study was to examine the length-weight relationships (LWR) of fish and invertebrate species exploited by the small-scale coastal fleet in the northern Aegean Sea (eastern Mediterranean Sea). Length and weight measurements were collected during experimental trials carried out seasonally from April 2016 to February 2017. A total of 4358 individuals from 31 species (28 fishes, 2 crustaceans and 1 cephalopod) representing 21 families were collected. With the exception of brown comber (Serranus hepatus) and rough ray (Raja radula), all LWR slopes fall within the 2.5 to 3.5 range. The median b value for fishes was 3.11 and 50% of the b values ranged between 3.04 and 3.24. Somatic growth was isometric for 14 species, hyperallometric for 12 species, while only 5 species grew hypoallometrically. This is the first reference on LWR for sand sole (Pegusa lascaris) in the eastern Mediterranean Sea, while for snake blenny (Ophidion barbatum), common cuttlefish (Sepia officinalis) and deep-water rose shrimp (Parapenaeus longirostris) it is the first LWR in Greek waters.

Determination of Usage Potential of Some Mediterranean Rays in Fish Oil Production

In this study, it was determined the chemical composition of the four ray species (Dasyatis pastinaca, Raja radula, Raja clavata and Torpedo marmorata) caught from Mersin Bay in the Northeastern Mediterranean Sea. For this purpose, lipid levels, fatty acid profiles, macro-trace elements, and heavy metal levels in the liver and muscle tissues of the Mediterranean rays were investigated. Lipid levels of liver tissue of D. pastinaca, R. radula, R. clavata, T. marmorata were determined to be 80.21%, 53.73%, 45.57% and 45.26%, respectively; while lipid levels for muscle tissue were 1.62%, 1.31%, 1.20% and 1.43%, respectively. In the fatty acid composition of muscle tissues of the rays; ∑SFAs (total saturated fatty acids) levels were reported to be between 30.46% and 35.00%, ∑MUFAs (total saturated fatty acids) levels were 21.49% to 27.77%, ∑PUFAs (total polyunsaturated fatty acids) levels were 28.76% to 35.69%; while for liver tissues; ∑SFAs levels were reported to be between 25.76% and 31.15%, ∑MUFAs levels were 23.43% to 30.66%, ∑PUFAs levels were 21.86% to 30.54%. According to data of this current study, no potential toxic metals (Cr, As, Cd, Pb, Hg) were detected in the fish oils obtained from the tissues. Finally, it was showed that these fish had potential for fish oil production because of their having fat in the liver tissues and there were also no potential heavy metal in the both muscle oil and liver oil, being rather healthy.

Morphological Abnormalities in Rajidae Species (Chondrichthyes) From the Gulf of Gabès (Tunisia, Central Mediterranean Sea): What Causes?

This study reports the occurrence of morphological abnormalities in four Rajidae specimens caught by a commercial trawler in the Gulf of Gabès (Tunisia, Central Mediterranean Sea): absence of tail and asymmetric pectoral fins in a female of the thornback ray <i>Raja clavata</i> Linnaeus, 1758 and absence of the caudal and dorsal fins in two female <i>Raja clavata</i> specimens and in one female Raja radula Delaroche, 1809 specimen. These cases of abnormality were described, commented and discussed.

Some biological aspects of juveniles of the rough ray, Raja radula Delaroche, 1809 in Eastern Sicily (central Mediterranean Sea)

Several biological aspects of juvenile specimens of Raja radula were investigated from February to May 2017 in the central Mediterranean Sea. Diet, sex ratio, disc width-weight relationships, and size-frequency distribution were analyzed. Stomach content analysis of 127 collected specimens showed that juveniles of R. radula actively feed on small benthic crustaceans, particularly on amphipods and isopods (Idotea balthica) (%IRI values of 62.74% and 12.39%, respectively). Although the Levin's index value (Bi = 0.44) indicated that juveniles of R. radula are a moderately stenophagous feeders, active mostly on crustaceans, the analysis of the prey-specific (Pi) biomass of the main preys vs. the frequency of their occurrence (%F) showed no clear dominance. The analysis of the sex ratio showed no significant difference in sex distribution. However, there were significant differences in mean size between sexes: females were, on average, larger than males, and also the b value (slope of the curve) of the disc width-weight relationships was higher in females.

Discards of elasmobranchs in a trammel net fishery targeting cuttlefish, Sepia officinalis Linnaeus, 1758, along the coast of Sicily (central Mediterranean Sea)

Several species of elasmobranchs are commonly found as bycatch or discard in both artisanal and industrial fisheries. In particular, in the Mediterranean Sea, only few studies are available about bycatch and discards of elasmobranchs in artisanal coastal fisheries. In this study, we focus our attention on elasmobranch catches in a trammel net fishery targeting cuttlefish (Sepia officinalis) in the southeastern Ionian coast of Sicily (central Mediterranean Sea). In 2017, during the peak S. officinalis fishing season (February–May), four species of the infraclass Batoidea (Raja radula, Dasyatis pastinaca, Torpedo marmorata and Torpedo torpedo) constituted the total elasmobranch catches of the 16 survey days. Catch per unit effort (CPUE) of T. torpedo, in both number of specimens and biomass terms, showed the highest value, accounting for about 50% of the total. Except for the three larger specimens of R. radula (1.7% of R. radula specimens caught), all elasmobranchs were discarded. An ANOVA showed significant differences (P<0.05) between monthly CPUE values of the four species; while, for each species, the chi-square test failed (P>0.05) to show a significant difference in monthly CPUE values. Average disc width of the specimens caught showed the overall presence of a large number of juveniles. Chi-square test for sex ratio showed a significant difference (P<0.05) only for T. torpedo. For D. pastinaca, survival rate was equal to 0. Local traditions play an essential role in fishermen’s choice to discard or retain fishes. Monitoring the impact of fishing on populations of these vulnerable or potentially vulnerable species is of fundamental importance for the development of management strategies.

Age, growth and length-weight relationship of the rough skate, Raja radula (Linnaeus, 1758) (Chondrichthyans: Rajidae), from the Gulf of Gabes (Tunisia, Central Mediterranean)

Age, growth and length-weight relationship of the rough skate, Raja radula (Linnaeus, 1758) (Chondrichthyans: Rajidae), from the Gulf of Gabes (Tunisia, Central Mediterranean)

Pelvic fin walking and punting behaviour of Raja radula Delaroche, 1809 observed in the Sea of Marmara

A mature female rough ray (Raja radula Delaroche, 1809) individual was observed at Sea of Marmara during a scuba dive to perform pelvic fin walking and punting, which was a previously unrecorded rajid behaviour from the Mediterranean Sea. The underwater video footage were analyzed, in which the average distance travelled per punt was measured as 0.40 disc length (DL) at an average speed of 0.26DL per second.

Pelvic fin walking and punting behaviour of Raja radula Delaroche, 1809 observed in the Sea of Marmara

A mature female rough ray (Raja radula Delaroche, 1809) individual was observed at Sea of Marmara during a scuba dive to perform pelvic fin walking and punting, which was a previously unrecorded rajid behaviour from the Mediterranean Sea. The underwater video footage were analyzed, in which the average distance travelled per punt was measured as 0.40 disc length (DL) at an average speed of 0.26DL per second.

Food habits of the rough ray Raja radula (Chondrichthyes: Rajidae) from the Gulf of Gabès (central Mediterranean Sea)

The food habits of rough ray Raja radula were investigated, with respect to sex, size and season, based on stomach content analyses of specimens collected from commercial fisheries, monthly during 2007 in the Gulf of Gabès (Central Mediterranean Sea). Of 950 stomachs examined, 183 were empty (19.26%). The overall diet of R. radula mainly consisted of crustacean decapods, teleosts and molluscs. Polycheates, sipunculids and echinoderms were minor dietary components. No differences were observed in the major preys consumed between the sexes, but ontogenetic and seasonal changes were found. The dietary trend with size shifted from crustaceans to teleosts. The consumptions of minor preys were independent from both size and season. Quantitative analysis and graphical methods indicated the rough ray to be a specialized feeder.

Age, growth and reproductive biology of the rough skate, Raja radula (Chondrichthyes: Rajidae), off the Gulf of Gabes (southern Tunisia, central Mediterranean)

Age, growth and reproductive parameters were estimated for Raja radula from the Gulf of Gabes (southern Tunisia, central Mediterranean Sea), collected monthly during 2007 from commercial fisheries. In total, 550 females (18.5–80.0 cm TL) and 400 males (13.4–65 cm TL) were examined to study the reproductive cycle. A subsample of 272 specimens (140 females and 132 males, ranging from 15.5 to 80 cm in total length, TL) was used for age and growth estimation derived from vertebral centra. The marginal-increment and edge analysis showed annual deposition of growth bands. The oldest female in the study was 12 years old and 80 cm in TL, whereas the oldest male was 9 years old and 65 cm in TL. The von Bertalanffy growth parameters were L∞ = 76.36 cm, K = 0.22 year–1 and t0 = –0.16 years for males. There was no significant difference in growth between the sexes. The size-at-maturity was 47.05 cm for males and 56.48 cm for females. The age-at-maturity was estimated to be 4.47 and 5.89 years, respectively, for males and females. There was no significant difference of size- and age-at-maturity between the sexes. Females carrying egg cases occurred throughout the year. Variations in the gonadosomatic and hepatosomatic indices showed a continuous reproductive cycle throughout the year.

Temporal changes in some Rajiformes species of cartilaginous fish (Chondrichthyes) from the west coast of İskenderun Bay (northeastern Mediterranean)

Some Rajiformes species among the cartilaginous fish (Chondrichthyes) that are distributed on the west coast of the Gulf of Iskenderun were seasonally obtained by bottom trawling from 2 different depth layers between the years 2004 and 2011. The spatiotemporal changes in catch per unit effort (CPUE) values were investigated by considering 2 depth contours (10 and 20 m). Six species belonging to 6 different Rajiformes families were identified during the sampling period, including Dasyatis pastinaca (common stingray), Gymnura altavela (spiny butterfly ray), Rhinobatos rhinobatos (common guitarfish), Raja radula (rough ray), Myliobatis aquila (common eagle ray), and Torpedo marmorata (marbled electric ray). A general linear model was used to analyze the changes in the total and separate weights of cartilaginous fish. For this purpose, the logarithms of CPUE values in weight were classed according to the depth, season, and years. Seasonal variations and year–season 2-way interactions were found to be highly significant for total cartilaginous CPUE values (P < 0.01). The annual changes in R. rhinobatos were the only significant annual difference (P < 0.05), while the year–season interactions of D. pastinaca were found to be significant (P < 0.01). The seasonal variations of D. pastinaca and G. altavela were also highly significant (P < 0.01).

Diet composition of juveniles of rough ray Raja radula (Chondrichthyes: Rajidae) from the Ionian Sea

The diet of juvenile specimens of Raja radula from the Ionian Sea was investigated. The stomach contents of 43 specimens were analysed in order to evaluate composite index (IRI Index of Relative Importance). To assess feeding strategy and trophic niche width, prey-specific biomass plotted against frequency of occurrence and Levins index were used, respectively. The diet of juvenile specimens of R. radula consisted mainly of crustacean decapods followed by algae, polychaetes and molluscs. Among crustaceans, Liocarcinus spp. were the most important prey items, with four species with relatively high IRI values. Most specimens had been feeding on L. pusillus, L. depurator and polychaetes, but the variation of prey-specific biomass indicates that there is not a clear dominance of any prey and the value of niche width indicates a high variability in R. radula diet. Differences between sexes exists only in % IRI values related to Liocarcinus spp. The results indicate that R. radula feeds on a wide range of prey items, although crustaceans were the favoured food source.

Characterization of a novel dermatan sulfate with high antithrombin activity from ray skin ( Raja radula)

Introduction A novel dermatan sulfate (DS) from the skin of the ray Raja radula with high anticoagulant activity was identified and its monosaccharide composition and anticoagulant mode of action and potency were determined. Materials and methods The DS isolated from the ray skin was identified by chondroitinase treatment and characterized by FT-IR and 1H NMR spectroscopy. Its anticoagulant activity was checked by activated partial thromboplastin time (aPTT), thrombin time (TT), thrombin generation (TG), heparin cofactor II (HCII) and antithrombin (AT)-mediated inhibition of thrombin. The effects on platelet activation and aggregation were investigated using flow cytometry and aggregometry, respectively. Results Chemical backbone structures of DS from Raja radula were close to that of DS from porcine intestinal mucosa. However, 1H NMR indicated that iduronic acid was the major hexuronic acid moiety in the ray skin DS and also suggested that the amount of 2-O-sulfonated iduronic acid was higher in comparison with mammalian DS along with the occurrence of 4-O-sulfonated N-acetylgalactosamine residues. The anticoagulant effect of the ray skin DS was mainly due to the potentiation of thrombin inhibition by HCII but also, although to a lesser extent, by AT and was higher than that of the DS standard. Moreover, it had no effect on platelet activation and aggregation induced by various agonists. Conclusion Altogether, these results indicated that DS from raja radula skin is an anticoagulant drug of interest potentially useful in anticoagulant therapy.

Mechanism of thrombin inhibition by heparin cofactor II and antithrombin in the presence of the ray ( Raja radula) skin dermatan sulfate

Introduction The kinetics of the thrombin inhibition by heparin cofactor II (HCII) and antithrombin (AT) have been studied as a function of the concentration of a dermatan sulfate (DS) from the skin of the ray Raja radula. Materials and methods The initial concentrations of inhibitor (I), HCII or AT, and thrombin (E) were set at equimolecular levels (3.10 - 9 M). Analysis of the experimental data obtained for DS concentrations ranging from 10 - 8 to 10 - 4 M was performed according to a previously described model in which DS binds quickly to the inhibitor and forms a complex more reactive than the free inhibitor towards thrombin. Results The apparent rate constant of the thrombin inhibition, k app, by either HCII or AT, increased in a concentration-dependent manner for DS concentrations up to 10 - 5 M or 10 - 6 M, respectively. At higher DS concentrations, k app remained unchanged for thrombin inhibition by HCII whereas a decrease in k app was observed for the thrombin-AT reaction. The dissociation constant of the polysaccharide-inhibitor complex, K DSI, and the rate constant of the thrombin inhibition by this complex, k, were (7.81 ± 0.75).10 - 7 M and (2.84 ± 0.42).10 9 M - 1 .min - 1 , whereas they were (4.93 ± 0.31).10 - 7 M and (2.47 ± 0.28).10 8 M - 1 .min - 1 , when the inhibitor was either HCII or AT, respectively. Conclusion DS from ray skin catalyzes the thrombin inhibition by HCII or AT primarily by forming a DS-inhibitor complex more reactive than the free inhibitor towards the protease. The affinity of DS for HCII was approximately 2-fold higher whereas the catalyzed reaction rate constant was approximately 20-fold higher when compared to AT.

Polysaccharides from the skin of the ray Raja radula. Partial characterization and anticoagulant activity

Introduction The polysaccharide fraction from the skin of the ray Raja radula was extracted, characterized and assayed for anticoagulant activity. Materials and methods A whole polysaccharidic fraction was extracted from the skin of the ray Raja radula by papain digestion followed by cetylpyridinium chloride and ethanol precipitation and was subjected to gel chromatography and anion exchange chromatography, acetate cellulose electrophoresis and characterized by physicochemical procedures. APTT and anti Xa assays were performed to assess the anticoagulant activity of the polysaccharidic fractions in comparison with unfractionated heparin. Results Gel and anion-exchange chromatography revealed two negatively charged polysaccharidic populations different in both molecular weight and charge. Infrared spectra suggested the occurrence of uronic acids and acetylated hexosamines. The second polysaccharide was highly sulfated, with a sulfate content of approximately 29%. These data suggested that dermatan sulfate (DS) is the sulfate rich polysaccharide whereas hyaluronic acid (HA) is the polysaccharide devoid of sulfate groups. Molecular mass characterization indicated that their average molecular masses were 22 kDa and 85 kDa, respectively. The sulfated polysaccharide, i.e. presumably DS, accounted alone for the observed concentration-dependent anticoagulant activity which was, as measured by APTT, 2 to 3-fold lower than that of heparin. In addition, it had a significant anti-Xa activity. Conclusion A major-sulfated polysaccharide, likely a dermatan sulfate, was extracted from the ray Raja radula skin. The results indicated that it exhibited a high anticoagulant activity and suggested that it was mediated by both heparin cofactor II and antithrombin.

Length–weight relationship for five elasmobranch species from the Cilician Basin shelf waters (Northeastern Mediterranean)

Summary In this study, elasmobranch length–weight relationships were estimated for five species caught between June 1999 and May 2003 from the Cilician Basin shelf waters (Northeastern Mediterranean): Raja clavata, Raja radula, Raja asterias, Dasyatis pastinaca, and Gymnura altavela. There were no significant differences between males and females, and only Raja clavata females showed isometric growth.