Chondrichthyan Fishes Research Articles

SkateBase, an elasmobranch genome project and collection of molecular resources for chondrichthyan fishes

Chondrichthyan fishes are a diverse class of gnathostomes that provide a valuable perspective on fundamental characteristics shared by all jawed and limbed vertebrates. Studies of phylogeny, species diversity, population structure, conservation, and physiology are accelerated by genomic, transcriptomic and protein sequence data. These data are widely available for many sarcopterygii (coelacanth, lungfish and tetrapods) and actinoptergii (ray-finned fish including teleosts) taxa, but limited for chondrichthyan fishes. In this study, we summarize available data for chondrichthyes and describe resources for one of the largest projects to characterize one of these fish, Leucoraja erinacea, the little skate. SkateBase ( http://skatebase.org) serves as the skate genome project portal linking data, research tools, and teaching resources.

SkateBase, an elasmobranch genome project and collection of molecular resources for chondrichthyan fishes.

Chondrichthyan fishes are a diverse class of gnathostomes that provide a valuable perspective on fundamental characteristics shared by all jawed and limbed vertebrates. Studies of phylogeny, species diversity, population structure, conservation, and physiology are accelerated by genomic, transcriptomic and protein sequence data. These data are widely available for many sarcopterygii (coelacanth, lungfish and tetrapods) and actinoptergii (ray-finned fish including teleosts) taxa, but limited for chondrichthyan fishes. In this study, we summarize available data for chondrichthyes and describe resources for one of the largest projects to characterize one of these fish, Leucoraja erinacea, the little skate. SkateBase ( http://skatebase.org) serves as the skate genome project portal linking data, research tools, and teaching resources.

Extinction risk and conservation of the world’s sharks and rays

The rapid expansion of human activities threatens ocean-wide biodiversity. Numerous marine animal populations have declined, yet it remains unclear whether these trends are symptomatic of a chronic accumulation of global marine extinction risk. We present the first systematic analysis of threat for a globally distributed lineage of 1,041 chondrichthyan fishes-sharks, rays, and chimaeras. We estimate that one-quarter are threatened according to IUCN Red List criteria due to overfishing (targeted and incidental). Large-bodied, shallow-water species are at greatest risk and five out of the seven most threatened families are rays. Overall chondrichthyan extinction risk is substantially higher than for most other vertebrates, and only one-third of species are considered safe. Population depletion has occurred throughout the world's ice-free waters, but is particularly prevalent in the Indo-Pacific Biodiversity Triangle and Mediterranean Sea. Improved management of fisheries and trade is urgently needed to avoid extinctions and promote population recovery. DOI: http://dx.doi.org/10.7554/eLife.00590.001.

An annotated checklist of the chondrichthyans of Taiwan

An annotated checklist of chondrichthyan fishes (sharks, batoids, and chimaeras) occurring in Taiwanese waters is presented. The checklist is the result of a biodiversity workshop held in Mach 2012 as well as on-going systematic revisions by the authors. The chondrichthyan fauna of Taiwan is one of the richest in the world with the number of species totaling 181, comprising 52 families and 98 genera. It includes 31 families, 64 genera, and 119 species of sharks, 19 families, 31 genera, and 58 species of batoids, and 2 families, 3 genera, and 4 species of chimaeras. The most species-rich families are the Carcharhinidae with 22 species followed by the Scyliorhinidae with 17. The most species-rich batoid families are the Dasyatidae with 11 species and and the Rajidae with 10. Verified voucher material is provided for each species where available and potential taxonomic issues are high-lighted when applicable. This represents the first detailed, evidence-based checklist of chondrichthyans from Taiwanese waters in over 40 years.

Differential occupation of axial morphospace

The postcranial system is composed of the axial and appendicular skeletons. The axial skeleton, which consists of serially repeating segments commonly known as vertebrae, protects and provides leverage for movement of the body. Across the vertebral column, much numerical and morphological diversity can be observed, which is associated with axial regionalization. The present article discusses this basic diversity and the early developmental mechanisms that guide vertebral formation and regionalization. An examination of vertebral numbers across the major vertebrate clades finds that actinopterygian and chondrichthyan fishes tend to increase vertebral number in the caudal region whereas Sarcopterygii increase the number of vertebrae in the precaudal region, although exceptions to each trend exist. Given the different regions of axial morphospace that are occupied by these groups, differential developmental processes control the axial patterning of actinopterygian and sarcopterygian species. It is possible that, among a variety of factors, the differential selective regimes for aquatic versus terrestrial locomotion have led to the differential use of axial morphospace in vertebrates.

A comparison of the electrosensory morphology of a euryhaline and a marine stingray

The electrosensory system is found in all chondrichthyan fishes and is used for several biological functions, most notably prey detection. Variation in the physical parameters of a habitat type, i.e. water conductivity, may influence the morphology of the electrosensory system. Thus, the electrosensory systems of freshwater rays are considerably different from those of fully marine species; however, little research has so far examined the morphology and distribution of these systems in euryhaline elasmobranchs. The present study investigates and compares the morphology and distribution of electrosensory organs in two sympatric stingray species: the (euryhaline) estuary stingray, Dasyatis fluviorum, and the (marine) blue-spotted maskray, Neotrygon kuhlii. Both species possess a significantly higher number of ventral electrosensory pores than previously assessed elasmobranchs. This correlates with a diet consisting of benthic infaunal and epifaunal prey, where the electrosensory pore distribution patterns are likely to be a function of both ecology and phylogeny. The gross morphology of the electrosensory system in D. fluviorum is more similar to that of other marine elasmobranch species, rather than that of freshwater species. Both D. fluviorum and N. kuhlii possess ‘macro-ampullae’ with branching canals leading to several alveoli. The size of the pores and the length of the canals in D. fluviorum are smaller than in N. kuhlii, which is likely to be an adaptation to habitats with lower conductivity. This study indicates that the morphology of the electrosensory system in a euryhaline elasmobranch species seems very similar to that of their fully marine counterparts. However, some morphological differences are present between these two sympatric species, which are thought to be linked to their habitat type.

BioSpotlight

BioTechniquesVol. 54, No. 6 BioSpotlightOpen AccessBioSpotlightPatrick C. H. Lo & Kristie NyboPatrick C. H. LoSearch for more papers by this author & Kristie NyboSearch for more papers by this authorPublished Online:3 Apr 2018https://doi.org/10.2144/000114034AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinkedInReddit Gene capture touches downNext-generation sequencing has been a major boon for evolutionary biologists interested in comparing the genomes of divergent species. In most cases, however, de novo whole genome sequencing of a previously uncharacterized species is impractical and often unnecessary given the time, labor, and cost. A far more efficient approach to exploring evolutionary relationships would be to sequence small groups of homologous genes using DNA hybridization capture technology (i.e. gene capture using bait sequences) or PCR. Gene capture is superior to PCR amplification for large-scale targeting of specific genes but tends to work best with closely related species or when baits are designed against highly conserved gene sequences within otherwise divergent genomes. Isolating genes whose sequences diverge significantly from the bait sequences has not been accomplished using current gene capture protocols. In this month's issue, Gavin Naylor and colleagues at the College of Charleston, (Charleston, SC) describe their new gene capture methodology that can isolate a predetermined set of protein-coding genes from species that have diverged by up to several hundred million years. The team first optimized the relaxed stringencies for the hybridization and washing steps from a previous touchdown hybridization gene capture scheme. Baits targeting single-copy protein-coding genes shared across six different gnathosome vertebrate species (human, western clawed toad, green anole, zebrafish, and elephant shark) were designed with up to 39% dissimilarity and separately constructed in custom biotinylated RNA bait libraries. Baits from each species were then used to capture selected target genes from distantly related species within the same class, which were then sequenced. When using standard hybridization and washing conditions, very few target sequences were obtained, whereas Naylor and colleagues’ touchdown scheme resulted in an eight-fold increase in captured sequences. Carrying out two rounds of capture further increased the number of targets obtained. This method also proved quite effective when applied to a diverse group of 13 chondrichthyan fishes, demonstrating that the technique was more consistent when used on a sample of more closely related taxonomic lineages. With this optimized gene capture protocol, researchers will be able to more effectively compare homologous genes across highly divergent taxa, further enhancing molecular phylogenetic studies.See “Capturing protein genes across highly divergent species”.Going digitalSince the concept of limiting dilution PCR was first introduced in BioTechniques in 1992, subsequent advances in methodology as well as microfluidic and array-based technologies have led to the digital PCR (dPCR) approaches available today. By partitioning samples into thousands of subreactions containing a single transcript each on a nanofluidic array, dPCR allows for binary reading of the results. A simple present or absent call for each subreaction allows near absolute quantification of DNA copy numbers, making dPCR especially attractive for transcript analysis in single cells where limited RNA content is a concern. Functional studies of single neurons have been conducted for years, relying on patch clamping techniques to record electrophysiological responses to particular stimuli. To detect gene expression changes accompanying those responses, researchers often harvest the cellular contents into the patch pipette. Subsequent RNA amplification allows for analysis of gene expression patterns, providing insight into the relationship between molecular and functional changes. In these experiments, transcript abundance is usually measured by real-time quantitative PCR (qRT-PCR), despite concerns about the sensitivity of this technique. Although access to dPCR technology is increasing, it has not yet been applied to these single neuron studies. Now, in this issue of BioTechniques, Farago et al. present a combined digital PCR–patch clamp electrophysiology method for assessing mRNA and miRNA expression in single neurons. The accuracy and sensitivity of this approach was validated using spike-in templates of known concentration. Precise copy number counts were obtained for transcripts of interest, even when expression levels were very low. Although dPCR technology remains expensive, coupling it with patch clamp extraction of cellular contents enables the collection of accurate and sensitive gene expression data for physiologically well-defined single neurons. The combination of dPCR and patch clamp promises improved accuracy for transcript analysis and will provide another option for researchers working with single cells.Application of spike-in template in dPCR analysis.Synthetic rps18 template (s_rps18) with subsequent dilution (0–81 copies per reaction).See “Digital PCR to determine the number of transcripts from single neurons after patch-clamp recording”.FiguresReferencesRelatedDetails Vol. 54, No. 6 Follow us on social media for the latest updates Metrics History Published online 3 April 2018 Published in print June 2013 Information© 2013 Author(s)PDF download

Egg capsule morphology provides new information about the interrelationships of chondrichthyan fishes

Chondrichthyan egg capsules have been well known since the nineteenth century, although their systematic affinities have been controversial for much of this time. Currently, 10 chondrichthyan egg capsule morphotypes are distinguished but their phylogenetic signal and evolutionary traits have not yet been analysed. Here, we present an analysis of all extant and currently known fossil chondrichthyan egg capsule types, and use a purported placoderm egg capsule as an outgroup for character coding. The phylogenetic hypothesis based on discrete morphological characters indicates that the enigmatic Carboniferous egg capsule morphotypes Crookallia and Vetacapsula form a monophyletic group together with the egg capsule morphotype of chimaerid holocephalans. The elasmobranch egg capsule morphotypes are sister to the holocephalan types. Based on these results we conclude that the ancestral chondrichthyan egg capsule morphotype combined features of those found in callorhinchid holocephalans and placoderms. From this ancestral type, two lineages of chondrichthyan egg capsule morphotypes diverged leading towards the major modern egg capsule morphotypes.

Species richness and distribution of chondrichthyan fishes in the Arctic Ocean and adjacent seas

The sea ice cover decreases and human activity increases in Arctic waters. Fisheries and bycatch issues, shipping and petroleum exploitation (pollution issues) make it imperative to establish biological baselines for the marine fishes inhabiting the Arctic Ocean and adjacent seas (AOAS). Species richness, zoogeographic affiliations and Red List statuses among chondrichthyan fishes (Chondrichthyes) were examined across 16 AOAS regions as a first step towards credible conservation actions. Published literature and museum vouchers were consulted for presence/absence data. Although many regions are poorly sampled, 49 chondrichthyan species have been reported from the AOAS. Skates and rays are the most species-rich taxon, represented by 27 species in family Rajidae and one species in family Dasyatidae. The sharks comprise 20 species in 13 families and the chimaeras one species in family Chimaeridae. The Norwegian Sea (28), Barents Sea (19) and Bering Sea (18) are particularly species-rich, and despite similar species numbers the two latter seas have no species in common. The remaining AOAS regions are inhabited by six species or less. Large-scale commercial fisheries for chondrichthyans are yet to be developed in the AOAS, but the precautionary principle should be implemented as abundances, basic taxonomy and biology are still largely unknown.

Validated age, growth and reproductive biology of Carcharhinus melanopterus, a widely distributed and exploited reef shark

Inadequate life-history information can compromise management of shark populations. The present study examined the life history of blacktip reef sharks (Carcharhinus melanopterus) from north-eastern Australia with predictions that they would show life-history patterns similar to those of other reef sharks species. Age and growth estimates were derived from vertebrae and five growth models. Males were 543–1390 mm total length (LST) and females were 514–1600 mm LST. Longevity was 10 years (males) and 15 years (females). Chemical marking confirmed annual band pair deposition but indicated probable age underestimation of large individuals. The logistic model was preferred (second-order Akaike information criterion (AICc) weight 0.7536), with growth parameter estimates of length at birth (L0) = 617 mm LST; asymptotic length (L∞) = 1585 mm LST; k (from logistic model) = 0.251 year–1. Males matured at 4.2 years (1050 mm LST) and females at 8.5 years (1335 mm LST), although further verification is needed. Mating and parturition occurred in summer and autumn, females having three or four pups per litter. Data were inconclusive in determining reproductive periodicity. These data contribute to the species management and conservation and suggest that the species may be sensitive to fishing pressure and habitat loss. The study also demonstrated potential complications in using vertebrae to estimate age and growth of chondrichthyan fishes.

A Case of Hermaphroditism in Tortonese's Stingray, <I>Dasyatis Tortonesei</I> (Elasmobranchii: Rajiformes: Dasyatidae) from the Lagoon of Bizerte, Tunisia

A normal hermaphrodite Tortonese’s stingray, Dasyatis tortonesei Capapé, 1975, captured in the brackish Lagoon of Bizerte (north-eastern Tunisia) is described in this note. It was a large specimen measuring 685 mm total length, 350 mm disk width, and 2190 g of the total body mass. The specimen externally presented medial cuspidate tooth rows on both jaws, and two claspers were present, that were rigid and calcified although shorter than those observed in normal specimens. The dissection of the abdominal cavity revealed on each side, an ovary normally developed that contained yolked oocytes, a complete genital tract and an uterus less developed than in normal adult. Conversely the testes were rudimentary, both Leydig’s glands were developed and a complete, slightly convoluted, male duct existed on the left side only. In all, 13 cases of normal (4) and abnormal (9) hermaphroditism, including the Tunisian D. tortonesei, have been found in batoid species, to date, confirming that the phenomenon is very rare among these chondrichthyan fishes.

A review of the taxonomy of chondrichthyan fishes: a modern perspective

Taxonomic clarity is a fundamental requirement as it forms the foundation of all other life sciences. In the last decade, chondrichthyan taxonomy has undergone a scientific renaissance with >180 new species formally described. This effort encompasses c. 15% of the global chondrichthyan fauna, which consists of 1185 currently recognized species. The important role of chondrichthyan taxonomy for conservation management has been highlighted in recent years with new species descriptions or taxonomic resolution of a number of threatened species. These include Australian gulper (genus Centrophorus) and speartooth sharks (genus Glyphis) in coastal waters of Australia and Borneo. Closer examination of other wide-ranging species, for which the taxonomy was thought to be stable, has shown that they consist of species complexes, e.g. manta rays (Manta spp.) and spotted eagle rays (the Aetobatus narinari complex), and highlights the need for critical re-examination of other wide-ranging species. Molecular methods have provided another useful tool to taxonomists and they have proven to assist greatly with identifying cryptic species and species complexes. The limitations of particular molecular methods being used need, however, to be carefully considered and there are some concerns about how these are being integrated with classical taxonomy. The fundamental importance of taxonomic nomenclature to life sciences is often poorly understood but striving for nomenclatural stability is a critical component of taxonomy. Similarly, biological collections are an extremely vital asset to both taxonomists and the broader scientific community. These collections are becoming increasingly important due in part to molecular species identification initiatives such as the Barcode of Life which has resulted in a large number of voucher specimens linked to tissue samples being deposited. Biological collections are also proving to be imperative in biodiversity studies as they contain a 'gold mine' of historical collection information important for assessing changes in faunal assemblages. Resources are typically limited for taxonomic research and the ageing taxonomic community is another issue of concern for the future of taxonomy on this important group. Succession planning and better resource allocation will be essential to ensure that this fundamental discipline is maintained into the future.

Body plan convergence in the evolution of skates and rays (Chondrichthyes: Batoidea)

Skates, rays and allies (Batoidea) comprise more than half of the species diversity and much of the morphological disparity among chondrichthyan fishes, the sister group to all other jawed vertebrates. While batoids are morphologically well characterized and have an excellent fossil record, there is currently no consensus on the interrelationships of family-level taxa. Here we construct a resolved, robust and time-calibrated batoid phylogeny using mitochondrial genomes, nuclear genes, and fossils, sampling densely across taxa. Data partitioning schemes, biases in the sequence data, and the relative informativeness of each fossil are explored. The molecular phylogeny is largely congruent with morphology crownward in the tree, but the branching orders of major batoid groups are mostly novel. Body plan convergence appears to be widespread in batoids. A depressed, rounded pectoral disk supported to the snout tip by fin radials, common to skates and stingrays, is indicated to have been derived independently by each group, while the long, spiny rostrum of sawfishes similarly appears to be convergent with that of sawsharks, which are not batoids. The major extant batoid lineages are inferred to have arisen relatively rapidly from the Late Triassic into the Jurassic, with long stems followed by subsequent radiations in each group around the Cretaceous/Tertiary boundary. The fossil record indicates that batoids were affected with disproportionate severity by the end-Cretaceous extinction event.

Body fluid osmolytes and urea and ammonia flux in the colon of two chondrichthyan fishes, the ratfish, Hydrolagus colliei, and spiny dogfish, Squalus acanthias

The present study has examined the role of the colon in regulating ammonia and urea nitrogen balance in two species of chondrichthyans, the ratfish, Hydrolagus colliei (a holocephalan) and the spiny dogfish, Squalus acanthias (an elasmobranch). Stripped colonic tissue from both the dogfish and ratfish was mounted in an Ussing chamber and in both species bi-directional urea flux was found to be negligible. Urea uptake by the mucosa and serosa of the isolated colonic epithelium through accumulation of 14C-urea was determined to be 2.8 and 6.2 fold greater in the mucosa of the dogfish compared to the serosa of the dogfish and the mucosa of the ratfish respectively. Furthermore, there was no difference between serosal and mucosal accumulation of 14C-urea in the ratfish. Through the addition of 2 mM NH 4Cl to the mucosal side of each preparation the potential for ammonia flux was also examined. This was again found to be negligible in both species suggesting that the colon is an extremely tight epithelium to the movement of both urea and ammonia. Plasma, chyme and bile fluid samples were also taken from the agastric ratfish and were compared with solute concentrations of equivalent body fluids in the dogfish. Finally molecular analysis revealed expression of 3 isoforms of the urea transport protein (UT) and an ammonia transport protein (Rhbg) in the gill, intestine, kidney and colon of the ratfish. Partial nucleotide sequences of the UT-1, 2 and 3 isoforms in the ratfish had 95, 95 and 92% identity to the equivalent UT isoforms recently identified in another holocephalan, the elephantfish, Callorhinchus milii. Finally, the nucleotide sequence of the Rhbg identified in the ratfish had 73% identity to the Rhbg protein recently identified in the little skate, Leucoraja erinacea.

“Camel nanoantibody” is an efficient tool for research, diagnostics and therapy

This short review provides an introduction to the rapidly developing field of generation and utilization of "camel nanoantibodies" (or "nanobodies"). The term "nanoantibody" or "nanobody" was given to single-domain variable fragments of special type of antibodies that naturally exist (in addition to classical types of antibodies) in blood of Camelidae family animals and in some chondrichthyan fishes. The existence of very efficient technology of nanobody generation and some very useful characteristic features promise a big potential for their use in immunobiotechnology and medicine.

Superfoetative viviparity in a Carboniferous chondrichthyan and reproduction in early gnathostomes

Chondrichthyan fishes have an evolutionary history spanning over 400 million years and are characterized, in part, by internal fertilization. Traditionally, oviparity has been assumed to be the primitive birthing mode for these fishes and for vertebrates in general, with viviparity and matrotrophic nutrition being derived. The fossilized remains of two specimens of Harpagofututor volsellorhinus from the Upper Mississippian of Montana now provide the first direct evidence of matrotrophic live birth in a Palaeozoic chondrichthyan and of superfoetation in an extinct fish. Each female exhibits multiple foetuses of two size groups, indicating simultaneous gestation of multiple litters. There is no evidence of yolk sacs, only preserved organic pigments enveloping the young, suggesting matrotrophically derived material. Young were born large, as head lengths of the largest embryos measured up to 66 per cent of the mother's head length. Comparison of in utero embryos to isolated specimens suggests, unlike all extant chondrichthyans, the absence of a juvenile stage and rapid maturity. These new data suggest the advantages of superfoetative viviparity for a small bodied fish in a 318 Myr old species- and predator-rich marine bay. In the greater view of gnathostome evolution, this finding combines with other recent discoveries to document that multiple, and not necessarily closely related, species of both placoderms and chondrichthyans exhibited viviparity by the Upper Devonian and the Upper Mississippian. The capacity for internal fertilization probably predisposed members of these lineages to develop viviparity so early in gnathostome history. Yet, the surprising range of viviparity exhibited at this stage of vertebrate evolution emphasizes that derived reproductive strategies had evolved in gnathostomes by 380–318 million years ago. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161, 587–594.

Chondrichthyan by-catch and discards in the demersal trawl fishery of the central Aegean Sea (Eastern Mediterranean)

Chondrichthyan (Chondrichthyes or cartilaginous) fishes, due to their special life history characteristics and the insufficient scientific information for the majority of them, constitute a very fragile resource of the world ocean, making their conservation a major concern. In Greece, a small portion of the chondrichthyan catch is marketed, 60% of which is produced by otter bottom trawls while other, more valuable species are targeted, and a large portion is usually discarded. A 10-year study in the Aegean Sea, divided into two sub-periods (1995–2000; 2003–2006) and based on bottom trawl fishery data, retroactively identified a total of 30 species making up 14.3% of the total catch in weight and 2.2% in number. A significant decrease in the chondrichthyan species richness, accompanied by an analogous decline in their abundance (catch composition and catch rate), was the most striking outcome. Species richness declined by an average of 0.66 species per year, and one third of the species collected during the earlier part of the study were absent from recent catches. Catch per unit of effort (CPUE) estimates in the mid-2000s were only half those in the mid-1990s. Although most species displayed a downward trend, certain Raja species displayed increased CPUE values in the recent years. More than 90% (in numbers) of the individuals caught were discarded at sea. The elasmobranch discards in the central Aegean included mainly Scyliorhinus canicula, Galeus melastomus and certain Raja species. It was clear that almost all the species were highly vulnerable since hatching due to the mesh currently in use, and there is a need to promote more selective gears. Although our findings provide signs of concern for the status of the chondrichthyan community in the study area, the processes influencing the population dynamics of the chondrichthyans are undoubtedly complex, and caution is needed in the interpretation of results. Further research based on surveys designed to place more emphasis on chondrichthyans is required and will contribute to the clarification of the observed trends.

Nuevos ejemplares y nuevos registros de peces cartilaginosos (Vertebrata: Chondrichthyes) de la costa del Pacífico mexicano

New specimens and new records of occurrence for 10 species of chondrichthyan (elasmobranch and chimaeroid) fishes previously unknown or little documented for the continental shelf of the Mexican Pacific are reported. This contribution provides the first record of Centroscyllium nigrum, Isurus paucus, and Bathyraja trachura for the Mexican Pacific, as well as new specimens of Hydrolagus colliei, Hexanchus griseus, Echinorhinus cookei, Pseudocarcharias kamoharai, and Raja velezi for the western coast of the Baja California Peninsula, including the intermediate record within the known distribution range for Apristurus kampae, and the southernmost record for Raja inornata.

Phylogenetic consistencies among chondrichthyan and teleost fishes in their bioaccumulation of multiple trace elements from seawater

Multi-tracer experiments determined the accumulation from seawater of selected radioactive trace elements (Mn-54, Co-60, Zn-65, Cs-134, Am-241, Cd-109, Ag-110m, Se-75 and Cr-51) by three teleost and three chondrichthyan fish species to test the hypothesis that these phylogenetic groups have different bioaccumulation characteristics, based on previously established contrasts between the carcharhiniform chondrichthyan Scyliorhinus canicula (dogfish) and the pleuronectiform teleost Psetta maxima (turbot). Discriminant function analysis on whole body: water concentration factors (CFs) separated dogfish and turbot in two independent experiments. Classification functions grouped the perciform teleosts, seabream ( Sparus aurata) and seabass ( Dicentrarchus labrax), with turbot and grouped the chondrichthyans, undulate ray ( Raja undulata; Rajiformes) and spotted torpedo ( Torpedo marmorata; Torpediniformes), with dogfish, thus supporting our hypothesis. Hierarchical classificatory, multi-dimensional scaling and similarity analyses based on the CFs for the nine radiotracers, also separated all three teleosts (that aggregated lower in the hierarchy) from the three chondrichthyan species. The three chondrichthyans were also more diverse amongst themselves compared to the three teleosts. Particular trace elements that were more important in separating teleosts and chondrichthyans were Cs-134 that was elevated in teleosts and Zn-65 that was elevated in chondrichthyans, these differences being due to their differential rates of uptake rather than loss. Chondrichthyans were also higher in Cr-51, Co-60, Ag-110m and Am-241, whereas teleosts were higher only in Mn-54. These contrasts in bioaccumulation patterns between teleosts and chondrichthyans are interpreted in the context of both proximate causes of underlying differences in physiology and anatomy, as well as the ultimate cause of their evolutionary divergence over more than 500 million years before present (MyBP). Our results and interpretation point to the possibility that radiation exposure regimes may be influenced by phylogeny, with implications for the adequacy of the marine reference organism approach in marine environmental protection.

First Determination of the Levels of Platinum Group Metals in Manta birostris (Manta Ray) Caught Along the Ghanaian Coastline

Tissues from Manta birostris caught by fishermen from Dixcove in the western part of Ghana were analyzed for their Platinum, palladium and rhodium concentrations (PGM). The use of chondrichthyan fish has permitted the study of trace levels of Platinum group metals (PGMs) which have travelled very far into the sea. The analysis showed that Ghana's coastline is fairly polluted with these platinum group metals (PGMs). PGM concentration in manta ray recorded a range of (0.15-0.85) microg/g for Pt, (0.033-0.67) microg/g for Pd and (0.007-0.145) microg/g for Rh. Comparing these values to the UK dietary intake of 0.2 microg/day for Pt and Rh and 1.0 microg/day for Pd, its indicates that the values obtained from the analysis for Pt was above the required level. This is the first study to show the accumulation of PGM in chondrichthyan fish, although the sources of this pollution are not clear as manta birostris is migratory and therefore need to be investigated further. The presence of the PGM is very significant, since manta ray meat is consumed in Ghana. This may presents a health risk, due to a possible accumulation of PGMs in humans.