Search

1. Determining how animals move within their environment is a fundamental knowledge that contributes to effective management and conservation. Continuous 'round-the-clock' animal movement data are frequently gathered using biotelemetry technology, providing discrete data packages on the presence-absence of animals at known locations through time. Current analyses of such data do not generally account for the interconnectivity of locations as animals move between them and consequently do not integrate graphically or statistically a temporal component to spatial changes. 2. Here, we describe the novel application of network analyses to electronic tag data whereby nodes represent locations and edges the movements of individuals. We demonstrate some of the descriptive and quantitative approaches for determining how an animal's movement interconnects home range habitats. Telemetry data from arrays of recorders provide movement data of individual animals, and as examples of the method proposed, we examine the movements of two distinct shark species, the small-spotted catshark ( Scyliorhinus canicula) and the Caribbean reef shark ( Carcharhinus perezi). In doing so, we consider both local and global network properties from an animal movement perspective and simulate the effects of node disruption as a proxy for habitat disturbance. 3. Comparative visual representations of two catshark movement networks suggest, for example, potential differences in space use. Multiple regression quadratic assignment procedure shows that habitat is a significant predictor of movement behaviour. 4. Null modelling of C. perezi movement data, corrected for the spatial restriction of static nodes, demonstrated a significant, non-random distribution of directed movements among sites. Additionally, the connectivity of this animal's movement network is significantly reduced through targeted disruption of a site of high centrality but not through disruption of a randomly selected site. 5. Network theory is a well-established theoretical framework and its integration into the fast developing field of animal movement and telemetry might improve significantly how we interpret animal space use from electronically recorded data. This technique has potentially wide application in animal behaviour but may also inform the management of habitat harbouring threatened or endangered species via the simulation, modelling and intuitive visualisation of animal movement interactions. [ABSTRACT FROM AUTHOR]

Abstract: Generalised Linear Models, combined with a Geographic Information System, were used to map the habitats of ten demersal elasmobranch taxa (five skates, four sharks and a stingray) in the eastern English Channel, based on an annual fishery-independent bottom trawl survey conducted each October, and covering 21years. Habitat models showing mean density levels were developed for the most frequently occurring species, whilst binomial occurrence habitat models were built for less frequent species. The main predictors of elasmobranch habitats in the eastern English Channel were depth, bed shear stress and salinity, followed by seabed sediment type and temperature. Habitat maps highlighted contrasting habitat utilisation across species. Raja clavata, and to a lesser extent Scyliorhinus canicula, showed ontogenetic differences in habitat utilisation, with early life history stages found in shallow coastal waters, sheltered from strong tidal currents and typically with softer sediments. Spatial segregation by sex was also evident for S. canicula, with females found at higher densities on some harder grounds in the study area. An improved knowledge of habitat utilisation by elasmobranchs (particularly for important life history stages and all seasons) is required if spatial management is to be considered for these species. [Copyright &y& Elsevier]

Here we present a detailed study of the major events in the retinal histogenesis in a slow-developing elasmobranch species, the small-spotted catshark, during embryonic, postnatal and adult stages using classical histological and immunohistological methods, providing a complete neurochemical characterization of retinal cells. We found that the retina of the small-spotted catshark was fully differentiated prior to birth. The major developmental events in retinal cell differentiation occurred during the second third of the embryonic period. Maturational features described in the present study were first detected in the central retina and, as development progressed, they spread to the rest of the retina following a central-to-peripheral gradient. While the formation of both plexiform layers occurs simultaneously in the retina of the most common fish models, in the small-spotted catshark retina the emergence of the outer plexiform layer was delayed with respect to the inner plexiform layer. According to the expression of the markers used, retinal cell differentiation followed a vitreal-to-scleral gradient, with the exception of Müller cells that were the last cell type generated during retinogenesis. This vitreal-to-scleral progression of neural differentiation seems to be specific to slow-developing fish species. [ABSTRACT FROM AUTHOR]

Abstract: Nitric oxide is a regulative molecule with important roles in the olfactory system of vertebrates. Chondrichtyans have a key position in vertebrate evolution and nothing is known about nitric oxide in their olfactory system. Aim of this work was to investigate the neuronal nitric oxide synthase (nNOS) immunoreactivity in the olfactory system of the shark Scyliorhinus canicula. Because nitric oxide is often related to GABA in the olfactory system, also the distribution of GABA and its synthesis enzyme GAD has been investigated. In the olfactory epithelium scattered cells in the basal and medial zone of the epithelium thickness presented nNOS-like immunoreactivity. In the olfactory bulb the nNOS-like immunoreactivity has been highlighted in nerve fibers around some blood vessels and in scattered GABAergic granule cells. The presence of nNOS in the olfactory system of S. canicula is overall lesser than that described in other vertebrates, even if nitric oxide probably keeps some essential functions. [Copyright &y& Elsevier]

Pax6 is involved in the control of neuronal specification, migration, and differentiation in the olfactory epithelium and in the generation of different interneuron subtypes in the olfactory bulb. Whether these roles are conserved during evolution is not known. Cartilaginous fish are extremely useful models for assessing the ancestral condition of brain organization because of their phylogenetic position. To shed light on the evolution of development of the olfactory system in vertebrates and on the involvement of Pax6 in this process, we analyzed by in situ hybridization and immunohistochemistry the expression pattern of Pax6 in the developing olfactory system in a basal vertebrate, the lesser spotted dogfish Scyliorhinus canicula. This small shark is becoming an important fish model in studies of vertebrate development. We report Pax6 expression in cells of the olfactory epithelium and olfactory bulb, and present the first evidence in vertebrates of strings of Pax6-expressing cells extending along the developing olfactory nerve. The results indicate the olfactory epithelium as the origin of these cells. These data are compatible with a role for Pax6 in the development of the olfactory epithelium and fibers, and provide a basis for future investigations into the mechanisms that regulate development of the olfactory system throughout evolution. J. Exp. Zool. (Mol. Dev. Evol.) 318:79-90, 2012. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The small-spotted cat shark (Scyliorhinus canicula) (Linnaeus, 1758) and the longnose spurdog (Squalus blainville) (Risso, 1826) are two species occurring in the European and western African continental shelves with a wide geographical distribution. In this study, the diet of S. blainville and S. canicula off the Portuguese western Atlantic coast was investigated in 2006 by collecting monthly samples of these two species from local fishing vessels. In the stomachs of both species, crustaceans and teleosts were the dominant prey items, and molluscs, polychaetes, echinoderms, and sipunculids were found in lower abundance. In S. canicula, urochordate and chondrichthyan species were also observed in stomachs and were classified as accidental prey items. Scyliorhinus canicula consumed a broader group of prey items than did S. blainville. A significant diet over- lap was observed, despite both species occupying different depth ranges over the continental shelf. Scyliorhinus canicula exhibited a consistency in diet composition among seasons, sexes, and maturity stages. Nonetheless, for both adults and juveniles, an increase in relative abundance of teleosts in the diet was observed in the spring and summer. This study provides evidence of the importance of S. canicula and S. blainville as benthic and pelagic predators along the western Atlantic coast. [ABSTRACT FROM AUTHOR]

Abstract: Immunohistochemical studies using antisera against various neuropeptides (Substance P, vasoactive intestinal polypeptide, and cholecystokinin octapeptide) and tyrosine hydroxylase revealed both olfactory sensory neuron (OSN) polymorphisms and transepithelial–subepithelial nerves in the olfactory epithelium of the cartilaginous fish, Scyliorhinus canicula. This study provides the first evidence of three morphological types of OSNs within the olfactory epithelium of cartilaginous fish that are similar to those found in the teleosts. In fishes there is evidence that OSNs differ functionally, including their differential olfactory bulb projections and molecular properties. The Substance P positive olfactory neurons in S. canicula may have a separate bulbar projection site that is not known, but may indicate a characteristic found in olfactory neuron subtypes in both lampreys and teleost fish. Numerous Substance P immunopositive nerves are found at the base of and in the olfactory epithelium. Some of them were observed to extend outwards almost reaching the epithelial surface. Their presumptive origin from the trigeminal nerve and their interrelationship with chemosensory cells in the nasal passages of vertebrates are discussed. [Copyright &y& Elsevier]

The Hox gene family encodes homeodomain-containing transcription factors involved in the patterning of structures composed of repeated elements along the antero-posterior axis of Bilateralia embryos. In vertebrate, Hox genes are thought to control the segmental identity of the rhombomeres, the branchial arches, and the somites. They are therefore thought to have played a key role in the morphological evolution of structures like the jaw, girdles, and vertebrae in gnathostomes. Thus far, our knowledge about the expression patterns of the Hox genes, the Hox code, has been mainly restricted to osteichthyans species and little is known about chondrichthyans. Recently, we identified 34 Hox genes clustered in three complexes (HoxA, HoxB, and HoxD) in the dogfish ( Scyliorhinus canicula) genome suggesting that in sharks most, if not all, genes belonging to the HoxC complex are lost. To gain insights into the evolution of gnathostome Hox transcription, we present here expression patterns along the anteroposterior axis for all Hox genes known in the dogfish. A comparison of these patterns with those of osteichthyans shows that the expression patterns of the Hox genes in serially homologous compartments such as the branchial arches, the hindbrain, and the somites underwent only subtle changes during the evolution of gnathostomes. Therefore, the nested expression of Hox genes in these structures, the Hox code, is a ground plan, which predates the morphological diversification of serially homologous structures along the body axis. [ABSTRACT FROM AUTHOR]

The article presents a study which examined gene expression data for spatio-temporal order of tooth initiation for Scyliorhinus canicula, teleosts in both oral and pharyngeal dentitions and Neoceratodus forsteri. The patterning mechanism observed for the oral and pharyngeal dentition is found to be unique to the vertebrate oro-pharynx and independent of the skin system. It is concluded that co-option of a successful iterative pattern occurred in evolution from mechanism that exists in the oro-pharynx of extinct agnathans.

To investigate the ability of elasmobranchs to distinguish between differing prey-type electric fields we examined the electroreceptive foraging behaviour of a model species, Scyliorhinus canicula (small-spotted catshark). Catshark preferences were studied by behaviourally conditioning them to swim through narrow tunnels, and on exit presenting them simultaneously with two different electric fields. Their subsequent choices of the following paired options were recorded; (i) Two artificial electric fields (dipole electrodes) with different magnitude direct current (D.C.), (ii) Two artificial electric fields, one D.C. and the other alternating current (A.C.), of the same magnitude, and (iii) similar magnitude, natural and artificial D.C. electric fields associated with shore crabs and dipole electrodes respectively. We found a highly significant preference for the stronger D.C. electric field and a less pronounced, but still significant, preference for the A.C. electric field rather than the D.C. electric field. No preference was demonstrated between the artificial and natural D.C. electric fields. The findings are discussed in relation to the animal's diet and ecology and with regard to anthropogenic sources of electric fields within their habitat. [ABSTRACT FROM AUTHOR]

Due to the impacts of commercial fishing on elasmobranchs, future research and management necessitates reliable and accurate information on life history. For females, maturity assessment is limited to dissection, and it is not desirable to be removing large numbers in order to assess the reproductive characteristics of a population. The present study evaluated ultrasonography as a potential, non-lethal method for assessing the maturity status of two oviparous elasmobranchs, the thornback ray ( Raja clavata) and small-spotted catshark ( Scyliorhinus canicula). Ultrasound permitted visualisation and measurement of the ovary in R. clavata, and the shell gland, ovarian follicles and egg capsules within the oviducts for S. canicula. With the exception of the ovary in R. clavata, the dimensions of these structures on the sonograms were directly corroborated by in situ measurements, and ultrasound was verified as an accurate and reliable method of making quantitative and qualitative assessments of these internal reproductive structures. [ABSTRACT FROM AUTHOR]

Abstract: To date, no study has been published on cell renewal in the olfactory epithelium of Chondrichthyes. Our work aimed at detecting proliferating cells (by Proliferating Cell Nuclear Antigen – PCNA immunohistochemistry) and apoptotic cells (by terminal uridine deoxynucleotidyl transferase nick end labeling method) in the olfactory epithelium of the shark Scyliorhinus canicula. PCNA immunoreactivity and mitotic figures were localized almost exclusively at the basal and apical thirds of the epithelial thickness. Double immunofluorescence for PCNA and OMP (a marker of mature olfactory neurons) showed that PCNA immunoreactivity is lacking in mature olfactory neurons, with the exception of crypt neurons. Crypt neurons, a cell type peculiar to fish, often showed PCNA immunoreactivity in the nucleus and may be involved in repair processes. The role of PCNA in mature crypt neurons requires further investigation to be clarified. Apoptosis was observed in sensory neurons and in basal cells. Our data highlight the presence of cell proliferation at different levels within the epithelium and the occurrence of apoptosis in both mature and proliferating cells. [ABSTRACT FROM AUTHOR]

It is now well established that there were four Hox gene clusters in the genome of the last common ancestor of extant gnathostomes. To better understand the evolution of the organization and expression of these genomic regions, we have studied the Hox gene clusters of a shark (Scyliorhinus canicula). We sequenced 225,580 expressed sequence tags from several embryonic cDNA libraries. Blast searches identified corresponding transcripts to almost all the HoxA, HoxB, and HoxD cluster genes. No HoxC transcript was identified, suggesting that this cluster is absent or highly degenerate. Using Hox gene sequences as probes, we selected and sequenced seven clones from a bacterial artificial chromosome library covering the complete region of the three gene clusters. Mapping of cDNAs to these genomic sequences showed extensive alternative splicing and untranslated exon sharing between neighboring Hox genes. Homologous noncoding exons could not be identified in transcripts from other species using sequence similarity. However, by comparing conserved noncoding sequences upstream of these exons in different species, we were able to identify homology between some exons. Some alternative splicing variants are probably very ancient and were already coded for by the ancestral Hox gene cluster. We also identified several transcripts that do not code for Hox proteins, are probably not translated, and all but one are in the reverse orientation to the Hox genes. This survey of the transcriptome of the Hox gene clusters of a shark shows that the high complexity observed in mammals is a gnathostome ancestral feature. [ABSTRACT FROM PUBLISHER]

Abstract: The calcium-binding protein calretinin (CR) has been widely used as a marker of neuronal differentiation. In the present study we analyzed the distribution of CR-immunoreactive (CR-ir) elements in the embryonic and postembryonic retina of two elasmobranchs, the lesser spotted dogfish (Scyliorhinus canicula) and the brown shyshark (Haploblepharus fuscus). We compared the distribution of CR with that of a proliferation marker (the proliferating cell nuclear antigen, PCNA) in order to investigate the time course of CR expression during retinogenesis and explored the relationship between CR and glutamic acid decarboxylase (GAD), the synthesizing enzyme of the gamma-aminobutyric acid (GABA), which has been reported to play a role in shark retinogenesis. The earliest CR immunoreactivity was concurrently observed in subsets of: a) ganglion cells in the ganglion cell layer; b) displaced ganglion cells in the inner plexiform layer and inner part of the inner nuclear layer (INLi); c) amacrine cells in the INLi, and d) horizontal cells. This pattern of CR distribution is established in the developing retina from early stage 32, long after the appearance of a layered retinal organization in the inner retina, and coinciding with photoreceptor maturation in the outer retina. We also demonstrated that CR is expressed in postmitotic cells long after they have exited the cell cycle and in a subset of GABAergic horizontal cells. Overall our results provide insights into the differentiation patterns in the elasmobranch retina and supply further comparative data on the development of CR distribution in the retina of vertebrates. This study may help in understanding the possible involvement of CR in aspects of retinal morphogenesis. [ABSTRACT FROM AUTHOR]

This study of Addisonia excentrica (Tiberi, 1855) is the first on the population dynamics of any cocculiniform limpet. We conducted 2 years of monthly sampling by trawling off the coast of Malaga province, Spain (Western Mediterranean), at 47–311 m. We sampled 482 egg cases of the lesser spotted dogfish (Scyliorhinus canicula), in which A. excentrica lives and feeds, which yielded 987 specimens of A. excentrica. Of capsules containing A. excentrica, 70.3% were collected between 50 and 100 m depth, where the mean percentage of occupied capsules (incidence) was 32.8%; the greatest incidence was found between 100 and 150 m (42.1%). The maximum depth of living A. excentrica was 222 m. In samples collected at 50–100 m recently settled individuals (<2 mm) predominated throughout the year. Larvae and apohermaphroditic specimens with mature oocytes (>7.2 mm) were scarce, but they were also present almost all year round, suggesting continuous reproduction. A positive correlation between the relative age of the egg case and the mean length of limpets was found. The long embryonic development of dogfish and the slow decay of egg cases provides enough time for larvae or young individuals to mature within a single egg case. Once mature, the limpets leave the capsule and spawn on the nearby bottom. Continuous reproduction and aggregated egg laying areas of the dogfish may improve the chances of larvae finding the egg cases during what is presumably a short larval life, and facilitate emigration of juveniles or large specimens to neighbouring capsules. Addisonia enodis Simone, 1996 is considered to be a junior synonym of A. excentrica. The larval shell of A. excentrica is described; it is very similar in shape and sculpture to the larval shell of Lepetella species, but larger. Newly settled specimens start to discard the protoconch at a size smaller than 0.4 mm. [ABSTRACT FROM PUBLISHER]

1. Metrics have become a standard way for summarizing environmental monitoring results. Different metrics react differently to natural variations and human-induced stressors. We suggest that combined analysis of time trends in selected biological metrics allows identification of biological processes (e.g. individual growth, mortality or recruitment) that have changed (increased or decreased) persistently. Alternatively, time trends in the abundance of sensitive species could indicate changes in environmental stressors. 2. We calculate the joint likelihood of time trends in three metrics and use it to evaluate the evidence in the data for different combinations of metric time trends. A simulation study provides guidelines for interpreting log-likelihood differences. 3. We illustrate the approach for identifying biological process changes for three North Sea fish stocks (cod Gadus morhua, lesser-spotted dogfish Scyliorhinus canicula and whiting Merlangius merlangius) using metrics derived from international bottom-trawl survey data for the period 1997–2008. Over the period, a decrease in recruitment and several simultaneous process changes were most likely for cod, while a recruitment increase, mortality decrease and several process changes were most likely for lesser-spotted dogfish. No significant persistent process changes were found for whiting. 4. Synthesis and applications. The likelihood approach offers a way of combining monotonic time trends in multiple metrics for identifying persistent changes in exploited populations or environmental stressors, given suitable metric time series and tables for interpreting joint time trends. For data rich fish populations, the proposed method can supplement analytical stock assessments. For many other populations with no fisheries-dependent data, it offers a way to identify population changes, which will be crucial for implementing the ecosystem approach to fisheries management and the European marine strategy framework directive. [ABSTRACT FROM AUTHOR]

Abstract: The annual and life-cycle mercury bioaccumulation pattern in selected tissues of the economically relevant Elasmobranchii species Scyliorhinus canicula was studied, and the risks associated with its consumption evaluated. Preferential mercury bioaccumulation occurred in muscle tissue, and followed the order muscle>heart>liver>gills>pancreas. Total mercury in muscle tissue ranged from 0.13mgkg−1 (wwt) in 1+year old males to 0.8mgkg−1 (wwt) in 8+ year old mature females, with no significant differences found between genders, and no clear lifespan bioaccumulation pattern observed, except for mature females. Organic mercury in the muscle ranged from 0.05mgkg−1 (wwt) to 0.52mgkg−1 (wwt), corresponding to an average of 70% of total mercury content. In mature females, a significant correlation (R =0.99, P =0.01) was found between size and organic mercury fraction, suggesting reproduction as an important factor controlling organic mercury bioaccumulation in the spotted dogfish. [ABSTRACT FROM AUTHOR]

A total of 325 small-spotted catsharks, Scyliorhinus canicula, ranging from 263 to 488 mm in total length (TL) and from 62 to 395 g in round weight (RW), were sampled from trawl catches in the Aegean Sea during the two-year period 2005-2007. The overall ratio of males to females was 1.06:1, and of the specimens almost 60% were mature. The size of mature males and females ranged between 371-488 mm and 364-467 mm in total length, respectively, while total length at 50% maturity was estimated at 396 mm for males and 399 mm for females. Ovary weight varied from 0.1 to 25.4 g and maximum oocyte diameter was 18 mm. Gonadosomatic indices ranged from 0.13 to 9.77 in female fish and from 0.25 to 6.36 in male fish, showing significant seasonal changes only in females (p-value < 0.05). Ovarian fecundity reached a maximum of 18 ripe oocytes in the ovary of a 460 mm TL female. Only one pair of egg cases was found in each one of the 30 adult females examined. [ABSTRACT FROM AUTHOR]

The mechanical performance of red and white muscle fibres from dogfish was compared during a long series of contractions with sinusoidal movement or under isometric conditions at 12°C (normal in vivo temperature). Power output was measured during sinusoidal movement at 0.75 Hz and peak-to-peak amplitude about 12% L0. Tetanus duty cycle was 33% (0.44 s) at phase -8% (first stimulus at 0.107 s before shortening started). Initially, the red fibres produced only about one third as much power as the white fibres, 6.57±0.63 W kg-1 wet mass (mean ± s.e.m.) and 18.3±2.3, respectively. Red fibres were better at sustaining power output; it declined rapidly to about 60% of its initial value and then remained relatively steady for up to 450 cycles of movement. Force during shortening declined, but force during stretch did not increase: force always relaxed to a low value before stretch started. By contrast, net power output by white fibres declined rapidly to zero within about 50 cycles. Two changes contributed: decline in force during shortening and an increase in force during stretch because relaxation became progressively less complete during the series of contractions. In isometric series (0.44 s stimulation every 1.33 s, cycle frequency 0.75 Hz), red and white fibres sustained peak isometric force similarly; in the 50th cycle force was 59±3% and 56±4% of initial values. The time required for force to relax to 10% of its maximum value decreased during the series for red fibres and increased for white fibres. [ABSTRACT FROM AUTHOR]

Abstract: In the dogfish (Scyliorhinus canicula L.) the testicular germinative zone (GZ), composed of large isolated spermatogonia surrounded by elongating pre-Sertoli cells, is located between the albuginea and the ventrolateral intratesticular vessel. During the spermatogenic wave, cysts radiate in maturational order forming distinct testicular zones. In this study, soluble proteins of the GZ and of the zone containing cysts with spermatocytes were separated by two-dimensional electrophoresis. Gel images were matched and then evaluated for GZ-specific proteins. From the1400 protein spots identified, 680 were found to be apparently specific to this zone. Using MALDI-TOF/TOF mass spectrometry, de novo sequences were obtained for 33 proteins out of the 169 selected for identification by mass spectrometry, but only 16 of these 169 proteins were identified. One of them, proteasome subunit alpha-6, was analyzed further by immunohistochemistry. This study demonstrates the utility of the dogfish as a model for proteome analysis of the spermatogonial stem cell niche, even if it remains restricted by the lack of genomic data available on Elasmobranchs. [Copyright &y& Elsevier]

Abstract: Recent studies indicate that elasmobranch fish respond differently to metal exposure than marine teleosts. Accumulation rates can be high, which despite the fact that normal background levels for metals in the marine environment are low, is worrying due to the long life span and late fecundity of most shark. The goals of the present study were to examine differences in accumulation rates and toxicity of a range of metals at equimolar concentrations (10µM) in the Mediterranean or spotted dogfish, Scyliorhinus canicula. For this purpose, we exposed the dogfish to Ni (587µg/L), Cd (1124µg/L), Pb (2072µg/L), Cu (635µg/L), and Ag (1079µg/L and two additional exposures at 10µg/L and 1µg/L) for one week and measured total metal accumulation, metallothionein induction, and parameters related to osmoregulation. Our study confirms the high toxicity and accumulation rates of Ag for elasmobranch fish, even at levels 100 to 1000 times lower than exposure levels of other metals. Also Pb accumulated readily in all organs, but did not cause any osmoregulatory disturbance at the exposure levels used. Ni and Cd seem to accumulate primarily in the kidney while Cu mainly accumulated in liver. In contrast to Ni and Cd, the three other metals Ag, Cu and Pb accumulated in the rectal gland, an important organ for osmoregulation and possible target organ for metal toxicity. Only Cu succeeded in initiating a protective response by inducing MT synthesis in liver and gills. [Copyright &y& Elsevier]

Abstract: We studied the pattern of cell proliferation and its relation with photoreceptor differentiation in the embryonic and postembryonic retina of two elasmobranchs, the lesser spotted dogfish (Scyliorhinus canicula) and the brown shyshark (Haploblepharus fuscus). Cell proliferation was studied with antibodies raised against proliferating cell nuclear antigen (PCNA) and phospho-histone-H3, and early photoreceptor differentiation with an antibody raised against rod opsin. As regards the spatiotemporal distribution of PCNA-immunoreactive cells, our results reveal a gradual loss of PCNA that coincides in a spatiotemporal sequence with the gradient of layer maturation. The presence of a peripheral growth zone containing pure-proliferating retinal progenitors (the ciliary marginal zone) in the adult retina matches with the general pattern observed in other groups of gnathostomous fishes. However, in the shark retina the generation of new cells is not restricted to the ciliary marginal zone but also occurs in retinal areas that contain differentiated cells: (1) in a transition zone that lies between the pure-proliferating ciliary marginal zone and the central (layered) retina; (2) in the differentiating central area up to prehatching embryos where large amounts of PCNA-positive cells were observed even in the inner and outer nuclear layers; (3) and in the retinal pigment epithelium of prehatching embryos. Rod opsin immunoreactivity was observed in both species when the outer plexiform layer begins to be recognized in the central retina and, as we previously observed in trout, coincided temporally with the weakening in PCNA labelling. [Copyright &y& Elsevier]

Chondroitin sulfate (CS), a constituent of proteoglycans, is a key component of the connective tissues and it is widely used as a precautionary drug for joint diseases; for this reason, the increased demand of this polysaccharide has posed the problem to identify new and secure sources of this product. In this context, CS from the cartilage of the lesser spotted dogfish (Scyliorhinus canicula, a cartilaginous fish) was isolated and investigated through chemical and spectroscopical techniques. The structural elucidation was performed on the entire polysaccharide and confirmed analyzing the products obtained via ABC lyase treatment. As a result, its compositional analysis disclosed the occurrence of CS-A, CS-C, CS-D, and CS-0S motifs in the ratio of 41, 32, 19.8, and 8.2%, respectively. Additionally, two different glycopeptides were isolated and characterized via NMR, providing information on the linkage oligosaccharide region joining the glycosaminoglycan chain to the core protein. Therefore, chondroitin sulfate from Scyliorhinus canicula appears very similar to that isolated from shark, a cartilaginous and taxonomically related fish, with the main difference residing in the major percentage of the CS-A motif. In the light of the results obtained, Scyliorhinus canicula chondroitin sulfate possesses a chemical structure compatible for the formulation of commercial and pharmaceutical products. [ABSTRACT FROM PUBLISHER]

It is essential to consider chondrichthyans (cartilaginous fishes) in analyzing ancestral brain organization because this radiation represents the out-group to all other living gnathostomes (jawed vertebrates). It is particularly crucial to understand the evolution of the telencephalon in chondrichthyans, as this structure develops by evagination (as in most other vertebrates), whereas in most osteichthyans (bony fishes), it develops by eversion, a markedly different process. Among chondrichthyans, the Lesser Spotted Dogfish Scyliorhinus canicula (Elasmobranchii) appears to offer the most potential as a model species for study. Developmental studies of Scyliorhinus have revealed a segmentary pattern in the developing forebrain, similar to that described in other vertebrates, as well as the occurrence of tangential cell migration within the telencephalon, especially in relation to the pallial-subpallial boundary. These observations indicate that major morphogenetic processes thought to be a hallmark of mammalian brains actually existed much earlier in vertebrate phylogeny. In addition, analysis of telencephalic development in Scyliorhinus indicates the existence of telencephalic structures that are probably related to the ganglionic eminences of mammals. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

To examine potential effects of male–female interactions on the sexes'' foraging behaviour, we studied equal-sized, single- and mixed-sex groups of a benthic elasmobranch, the small-spotted catshark, in response to electric stimuli. A total of 88 size-matched, adult individuals were repeatedly presented with a range of artificial, prey type electric fields (E fields) under laboratory conditions in groups of (1) four males, (2) four females and (3) two of each sex. Females in single-sex groups were more responsive towards E fields than both single- and mixed-sex group males, despite showing similar activity levels. Equally, females in mixed-sex groups were more responsive than males in mixed groups, but showed similar activity levels. Furthermore, females in mixed-sex groups were less responsive to E fields than females from single-sex groups, despite showing similar activity levels. Males in mixed-sex groups were less responsive than males in single-sex groups, but were more active. These results indicate more intense foraging behaviour among females than males and significant reductions in foraging behaviour when grouped with the opposite sex. Both findings are probably associated with consequences of differing reproductive strategies and resultant sexual conflict (specifically male harassment and female avoidance). [Copyright &y& Elsevier]

We explored the molecular mechanisms of morphological transformations of vertebrate paired fin/limb evolution by comparative gene expression profiling and functional analyses. In this study, we focused on the temporal differences of the onset of Sonic hedgehog (Shh) expression in paired appendages among different vertebrates. In limb buds of chick and mouse, Shh expression is activated as soon as there is a morphological bud, concomitant with Hoxd10 expression. In dogfish (Scyliorhinus canicula), however, we found that Shh was transcribed late in fin development, concomitant with Hoxd13 expression. We utilized zebrafish as a model to determine whether quantitative changes in hox expression alter the timing of shh expression in pectoral fins of zebrafish embryos. We found that the temporal shift of Shh activity altered the size of endoskeletal elements in paired fins of zebrafish and dogfish. Thus, a threshold level of hox expression determines the onset of shh expression, and the subsequent heterochronic shift of Shh activity can affect the size of the fin endoskeleton. This process may have facilitated major morphological changes in paired appendages during vertebrate limb evolution. [ABSTRACT FROM AUTHOR]

Abstract: The genetic mechanisms, which control axis specification, apparently extensively diverge across vertebrates. In amphibians and teleosts, they are tightly linked to the establishment of an early dorso-ventral polarity. This polarity has no equivalent in amniotes, which unlike the former, retain a considerable plasticity for their site of axis formation until blastula stages and rely on signals secreted by extra-embryonic tissues for the establishment of their early rostro-caudal pattern. In order to better understand the links between these seemingly highly divergent mechanisms, we have used an evo-devo approach, aimed at reconstructing the gnathostome ancestral state and focussed on a chondrichthyan, the dogfish Scyliorhinus canicula. A detailed molecular characterization of the dogfish embryo at blastula and gastrula stages highlights striking similarities with all vertebrate model organisms including amniotes. It suggests the presence in the dogfish of territories homologous to the hypoblast and extra-embryonic ectoderm of the latter, which may therefore reflect the primitive condition of jawed vertebrates. In the ancestral state, these territories are specified at opposite sides of an early axis of bilateral symmetry, homologous to the dorso-ventral axis of amphibians and teleosts, and aligned with the later forming embryonic axis, from head to tail. Amniotes have diverged from this pattern through a posterior expansion of extra-embryonic ectoderm, resulting in an apparently radial symmetry at late blastula stages. These data delineate the broad outlines of the gnathostome ancestral pattern of axis specification and highlight an unexpected unity of mechanisms across jawed vertebrates. They illustrate the complementarity of comparative and genetic approaches for a comprehensive view of developmental mechanisms themselves. To cite this article: M. Coolen et al., C. R. Biologies 332 (2009). [Copyright &y& Elsevier]

Simple Summary: For the first time, glucocorticoid actions of corticosteroids are evidenced in vivo and ex vivo in sharks, highlighting the importance of carbohydrate metabolism in situations of high-energy expenditure in this taxonomical group. Long-term (7 days) in vivo administration of dexamethasone (DEX, a synthetic glucocorticoid) decreased 1α-hydroxycorticosterone (1α-OHB, the main corticosteroid hormone in sharks), while also modified carbohydrates metabolism in liver and white muscle. Short-term (1 to 5 h) ex vivo incubation of liver and muscle explants with cortisol (corticosteroid not present in sharks) and DEX revealed glucose secretion mediated by glucocorticoid receptors (GR), as seen by the employment of mifepristone (a GR inhibitor). Corticosteroids are hormones produced in vertebrates exerting gluco- and mineralocorticoid actions (GC and MC) mediated by specific receptors (GR and MR, respectively). In elasmobranchs, the major circulating corticosteroid is the 1α-hydroxycorticosterone (1α-OHB). This hormone acts as a MC, but to date its role as a GC has not been established. As there is no 1α-OHB standard available, here we employed a set of in vivo and ex vivo approaches to test GC actions of other corticosteroids in the lesser spotted catshark (Scyliorhinus canicula). Dexamethasone (DEX, a synthetic corticosteroid) slow-release implants decreased plasma 1α-OHB levels after 7 days, and modified carbohydrates metabolism in liver and white muscle (energy stores and metabolic enzymes). In addition, ex vivo culture of liver and white muscle explants confirmed GC actions of corticosteroids not naturally present in sharks (cortisol and DEX) by increasing glucose secretion from these tissues. Dose–response curves induced by cortisol and DEX, altogether with the use of specific GR inhibitor mifepristone, confirmed the involvement of GR mediating glucose secretion. This study highlights the influence of corticosteroids in the glucose balance of S. canicula, though the role of 1α-OHB as a GC hormone in sharks should be further confirmed. [ABSTRACT FROM AUTHOR]

Abstract: Calretinin immunohistochemistry was used to study the organization of some cerebellar structures and lateral line medullary nuclei of an elasmobranch, the lesser-spotted dogfish Scyliorhinus canicula. In the cerebellar molecular layer, stellate cells are strongly calretinin-immunoreactive (CR-ir). Perikarya and dendrites of Purkinje cells are contacted by numerous stellate cell small CR-ir boutons. Some Purkinje cell perikarya are contacted by CR-ir climbing fibers forming complex axo-somatic contacts. In the granular layer, numerous CR-ir mossy fibers exhibited large swellings. Notable differences in density and diameter of mossy fibers are observed between the auricles and cerebellar body. Thin beaded CR-ir fibers are also present in the granular layer of the body. The lateral line nuclei of the octavolateralis region are comprised of a molecular-like cerebellar crest that covers the dorsal (electroreceptive) and the medial octavolateralis nuclei (mechanoreceptive). The cerebellar crest exhibited numerous CR-ir stellate cells. In the dorsal octavolateralis nucleus, the presence of conspicuous CR-ir cells and neuropil closely associated to the region of primary fiber terminals distinguishes it clearly from the medial nucleus, revealing major differences between the electroreceptive and mechanoreceptive primary nuclei of elasmobranchs. Moreover, CR distribution in the dogfish cerebellum showed interesting differences with those reported in cerebella of other vertebrates, indicating a high variability of cerebellar CR expression in phylogeny. [Copyright &y& Elsevier]

A technique using 51chromium-labelled erythrocytes was used to measure blood volume in Scyliorhinus canicula following long-term and acute salinity transfers. Basal whole-blood volume was 5·6 ± 0·2 ml 100 g−1 (mean ±s.e.), this increased (6·3 ± 0·2 ml 100 g−1) following +14 day acclimation to 80% sea water (SW) and decreased (4·6 ± 0·2 ml 100 g−1) following acclimation to 120% SW. These changes were shown to be primarily due to changes in plasma volume, with no significant changes in extrapolated red-cell volume being demonstrated. Blood volume was also measured in the same animals during 10 h acute transfer to 100% SW. Plasma volume in S. canicula during acclimation from 80% SW was significantly reduced (4·5 ± 0·3 ml 100 g−1) after 6 h of transfer to 100% SW. Blood volume in animals during acclimation from 120% SW was significantly increased (4·8 ± 0·2 ml 100 g−1) after 4 h of acute transfer. The osmoregulatory implications of these different timeframes during hyposaline and hypersaline transfer are discussed, along with the importance of this in vivo technique as context for in vitro studies with haemo-dynamic stimuli. [ABSTRACT FROM AUTHOR]

Radiotracer experiments using 210Pb and 203Hg demonstrated that eggs of the spotted dogfish Scyliorhinus canicula absorbed lead and inorganic mercury directly from seawater over 21 days of experimental exposure, attaining total egg concentration factors (CFs) relative to water of approximately 400 for Pb and 180 for Hg, predominantly (≥98%) due to their accumulation by the collagenous egg case. The rates of accumulation of both Pb and Hg by the total egg were significantly ( P < 0.0001) reduced by its increasing age since parturition, whereas only the rate of depuration of Pb was reduced ( P < 0.0001) with increasing age; these effects indicate a declining chemical reactivity of the egg case that may be due to the continued tanning of the case following parturition. The egg case per se, attained average CFs of about 1,500 and 850 for Pb and Hg, respectively. Both Pb and Hg showed declining concentration gradients from the exterior to the interior membranes of the wall of the egg case; CFs for Pb declined from 3,500 to 2,000 and for Hg from 5,000 to 500. Comparison of concentrations in separate membranes also demonstrated significant ( P ≤ 0.01) depurations of Hg from the external and internal membranes during the loss experiments. The presence of radiotracers of Pb and Hg in the internal components of the egg at the end of uptake phase, and prior to the opening of the apertures, confirmed the permeability of the egg case wall to them, consistent with their observed gradients in it. The average CFs for all embryos at the end of the uptake experiment were 34 and 44 for Pb and Hg, respectively, but were significantly ( P < 0.001) enhanced for Hg by a factor of 6 in the older eggs. The accumulatory and kinetic characteristics of the egg-case may operate to optimize the exposure of embryos to Pb and Hg following episodic contaminant events in coastal habitats. [ABSTRACT FROM AUTHOR]

Abstract: This study examines the effects of certain closed areas to the trawl fishery on some Rajidae species and small-spotted catshark in the southern area of the Bay of Biscay. The results are based on abundance index (number/haul) and catch length composition obtained from a series of bottom trawl surveys carried out in the area (1993–2005). Abundance trends are similar considering or not closed areas, but with much lower values excluding closed areas. The length distributions revealed that in some of the species like Scyliorhinus canicula the larger specimens were the most affected by this decrease in number. Finally, the effects and consequences of one of these marine protected areas (MPAs), an artificial reef were examined in more detail for all the fishes and invertebrates. The analysis of the yield series showed an increase in total biomass after the placement of the reefs not only for S. canicula and rays but also teleosts fishes like Pagellus acarne, Trachurus trachurus, Mullus surmuletus and Trachinus draco and particularly invertebrates (sea urchins). On the contrary, the main target species of the trawl fishery (hake, monkfish and megrim among others) did not increase. [Copyright &y& Elsevier]

In the lesser-spotted dogfish ( Scyliorhinus canicula), spermatogenesis takes place within spermatocysts made up of Sertoli cells associated with stage-synchronized germ cells. As shown in testicular cross sections, cysts radiate in maturational order from the germinative area, where they are formed, to the opposite margin of the testis, where spermiation occurs. In the germinative zone, which is located in a specific area between the tunica albuginea of the testis and the dorsal testicular vessel, individual large spermatogonia are surrounded by elongated somatic cells. The aim of this study has been to define whether these spermatogonia share characteristics with spermatogonial stem cells described in vertebrate and non-vertebrate species. We have studied their ultrastructure and their mitotic activity by 5′-bromo-2′-deoxyuridine (BrdU) incorporation and proliferating cell nuclear antigen (PCNA) immunodetection. Additionally, immunodetection of c-Kit receptor, a marker of differentiating spermatogonia in rodents, and of α- and β-spectrins, as constituents of the spectrosome and the fusome, has been performed. Ultrastructurally, nuclei of stage I spermatogonia present the same mottled aspect in dogfish as undifferentiated spermatogonia nuclei in rodents. Moreover, intercellular bridges are not observed in dogfish spermatogonia, although they are present in stage II spermatogonia. BrdU and PCNA immunodetection underlines their low mitotic activity. The presence of a spectrosome-like structure, a cytological marker of the germline stem cells in Drosophila, has been observed. Our results constitute the first step in the study of spermatogonial stem cells and their niche in the dogfish. [ABSTRACT FROM AUTHOR]

This study evaluated the influence of environment (substratum type and depth) on the electroreception capabilities of small spotted catsharks Scyliorhinus canicula in response to prey-simulating electric fields. In experiments where electric fields (applied current 15 μA) were presented beneath different substrata (sand, pebbles, rocks and control) it was found that search effort was not different between substrata or S. canicula sexes, however, both rates of turning and biting towards active electrodes were decreased over pebbles and rocks compared with sand and the control (no substratum). There was no significant effect of sex on turn and bite rates over any substrata. Electric fields were then presented beneath different depths of sand to examine the depth-limits of fish electroreception. Turn and bite rates were significantly lower at depths below 10 mm, with no bites towards electrodes made when they were >30 mm depth. Search effort was not found to be different between different burial depth treatments or between sexes. These results indicate substratum type and depth influences the ability of S. canicula to detect prey-simulating electric fields. This variation in electroreceptive performance may influence space use of sharks. [ABSTRACT FROM AUTHOR]

Jaw viscoelasticity of newborn and adult lesser spotted dogfish Scyliorhinus canicula was measured using dynamic mechanical analysis. Jaws of newborn animals were significantly more viscoelastic than those of adults. As a result, newborn lesser spotted dogfish might be unable to consume hard prey items, unlike adults. [ABSTRACT FROM AUTHOR]

Single-unit recordings were performed from a retinorecipient pretectal area (corpus geniculatum laterale) in Scyliorhinus canicula. The function and homology of this nucleus has not been clarified so far. During visual stimulation with a random dot pattern, 45 (35%) neurons were found to be direction selective, 10 (8%) were axis selective (best neuronal responses to rotations in both directions around one particular stimulus axis), and 75 (58%) were movement sensitive. Direction-selective responses were found to the following stimulus directions (in retinal coordinates): temporonasal and nasotemporal horizontal movements, up- and downward vertical movements, and oblique movements. All directions of motion were represented equally by our sample of pretectal neurons. Additionally we tested the responses of 58 of the 130 neurons to random dot patterns rotating around the semicircular canal or body axes to investigate whether direction-selective visual information is mapped into vestibular coordinates in pretectal neurons of this chondrichthyan species. Again all rotational directions were represented equally, which argues against a direct transformation from a retinal to a vestibular reference frame. If a complete transformation had occurred, responses to rotational axes corresponding to the axes of the semicircular canals should have been overrepresented. In conclusion, the recorded direction-selective neurons in the Cgl are plausible detectors for retinal slip created by body rotations in all directions. [ABSTRACT FROM AUTHOR]

Abstract: The FoxL2 genes are a subfamily of the Fox (forkhead box) gene family. FOXL2 is mutated in the disorder Blepharophimosis, Ptosis, and Epicanthus Inversus Syndrome (BPES), which is characterized by eyelid malformations, and Premature Ovarian Failure (POF). In the mouse expression is seen in the perioptic mesenchyme, developing eyelids, ovary and pituitary. We have isolated a foxl2 cDNA from the dogfish Scyliorhinus canicula (also known as the lesser spotted catshark), allowing the characterisation of this gene’s sequence and expression from a lineage that diverged early in the evolution of gnathostomes. Molecular phylogenetic analysis strongly grouped this sequence with the gnathostomes within the FoxL2 subfamily. We demonstrate the early expression of Scyliorhinus canicula foxl2 in the mandibular head mesoderm and later in continuous populations of mandibular arch cells and mandibular head mesenchyme cells around the developing pituitary. As development proceeds expression decreases in the mesenchyme of the head but is seen in the mesenchyme around the eye and later in the developing eyelids. Additionally expression is seen in regions of pharyngeal arch mesoderm and in ectoderm from which gill buds will form. This expression is maintained in the developing and elongating gill buds. Thus, S. canicula foxl2 is a marker for the mandibular mesoderm and gill buds and its expression is conserved in the perioptic mesenchyme, developing eyelids and pituitary. [Copyright &y& Elsevier]

The saccus vasculosus (SV) is a circumventricular organ of the hypothalamus of many jawed fishes whose functions have not yet been clarified. It is a vascularized neuroepithelium that consists of coronet cells, cerebrospinal fluid-contacting (CSF-c) neurons and supporting cells. To assess the organization, development and evolution of the SV, the expression of glial fibrillary acidic protein (GFAP) and the neuronal markers γ-aminobutyric acid (GABA), glutamic acid decarboxylase (GAD; the GABA synthesizing enzyme), neuropeptide Y (NPY), neurophysin II (NPH), tyrosine hydroxylase (TH; the rate-limiting catecholamine-synthesizing enzyme) and serotonin (5-HT), were investigated by immunohistochemistry in developing and adult sharks. Coronet cells showed GFAP immunoreactivity from embryos at stage 31 to adults, indicating a glial nature. GABAergic CSF-c neurons were evidenced just when the primordium of the SV becomes detectable (at stage 29). Double immunolabeling revealed colocalization of NPY and GAD in these cells. Some CSF-c cells showed TH immunoreactivity in postembryonic stages. Saccofugal GABAergic fibers formed a defined SV tract from the stage 30 and scattered neurosecretory (NPH-immunoreactive) and monoaminergic (5-HT- and TH-immunoreactive) saccopetal fibers were first detected at stages 31 and 32, respectively. The early differentiation of GABAergic neurons and the presence of a conspicuous GABAergic saccofugal system are shared by elasmobranch and teleosts (trout), suggesting that GABA plays a key function in the SV circuitry. Monoaminergic structures have not been reported in the SV of bony fishes, and were probably acquired secondarily in sharks. The existence of saccopetal monoaminergic and neurosecretory fibers reveals reciprocal connections between the SV and hypothalamic structures which have not been previously detected in teleosts. Copyright © 2007 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

An experimental study examined the 96-h net influx from seawater of the anthropogenic radionuclides 241Am, 60Co and 134Cs through the egg-case of the spotted dogfish Scyliorhinus canicula. Net influx directly through the wall of the egg-case was greatest for 134Cs, then 241Am and lastly 60Co. Within the egg-case wall itself the measured concentration factors (CFs) and their gradients in the external, median and internal layers showed that for both 241Am and 60Co they were >103 in the external layer and declined by an order of magnitude in the interior layer. In contrast 134Cs had a CF of only about three in the external layer which declined by a factor of 2 towards the two more internal layers of the egg-case. The egg-case apertures, that open within the prehatching stage of embryological development, significantly (P <0.05) increased the net influx of 241Am and 60Co to the interior of the egg-case, although their water concentrations were still lower than those in the labelled seawater bath. In contrast, the aperture did not increase the net influx of 134Cs whose water concentrations equilibrated with those in seawater. Together these results indicate that the egg-case wall is very permeable to 134Cs, representing little barrier to its movement, and hence consistent with the lack of importance of the aperture in determining its internal water concentrations in the egg-case. In contrast, 241Am and 60Co show much higher rates of accumulation by the egg-case, consistent with the measured reduced permeability of its wall, and therefore giving greater prominence to its aperture in the net transfer of these two radionuclides to the egg case’s interior. The presence of the embryo within its egg-case did not significantly (P >0.05) affect the rates of influx of radioisotopes, with the exception of an interactive effect for 60Co with the egg-case aperture (P <0.05). The CF of only 241Am in the embryo itself relative to the external seawater concentration was significantly (P <0.05) enhanced by the presence of the aperture. [Copyright &y& Elsevier]

The influence of factors such as depth, near bottom temperature, near bottom salinity, fish length and diet composition on the aggregation of Scyliorhinus canicula in the Cantabrian Sea was examined. The correlation between these variables and the aggregations of each sex was low. A priori juvenile males and females were not highly discriminated by any of these environmental variables (depth, temperature and salinity) based on a multivariate analysis. The best discriminated groups were the new recruits, and depth and longitude were the variables that contributed most to their segregation, while adult males had some preference for shallower and warm waters. Diet composition varied with body size but it was quite similar in both sexes among which no significant differences were observed. An increase in feeding intensity and abundance of Euphasiacea prey taxa was found in adult females compared to males. [ABSTRACT FROM AUTHOR]

Abstract: In order to gain insight into the evolution of the genetic control of the development of cranial neurogenic placodes and cranial sensory ganglia in vertebrates, we cloned and analysed the spatiotemporal expression pattern of six transcription factor genes in a chondrichthyan, the shark Scyliorhinus canicula (lesser-spotted dogfish/catshark). As in other vertebrates, NeuroD is expressed in all cranial sensory ganglia. We show that Pax3 is expressed in the profundal placode and ganglion, strongly supporting homology between the separate profundal ganglion of elasmobranchs and basal actinopterygians and the ophthalmic trigeminal placode-derived neurons of the fused amniote trigeminal ganglion. We show that Pax2 is a conserved pan-gnathostome marker for epibranchial and otic placodes, and confirm that Phox2b is a conserved pan-gnathostome marker for epibranchial placode-derived neurons. We identify Eya4 as a novel marker for the lateral line system throughout its development, expressed in lateral line placodes, sensory ridges and migrating primordia, neuromasts and electroreceptors. We also identify Tbx3 as a specific marker for lateral line ganglia in shark embryos. We use the spatiotemporal expression pattern of these genes to characterise the development of neurogenic placodes and cranial sensory ganglia in the dogfish, with a focus on the epibranchial and lateral line placodes. Our findings demonstrate the evolutionary conservation across all gnathostomes of at least some of the transcription factor networks underlying neurogenic placode development. [Copyright &y& Elsevier]

The action spectrum of the electroretinographic (ERG) b-wave and the unmasked late receptor potential (LRP) were measured under a variety of conditions (isolated eyecup, detached retina, b-wave recording in fresh preparations, LRP measurements after low-temperature aging, dark and light adaptation). It was shown that in the dogfish, Scyliorhinus canicula (L.), eyecup spectral sensitivity matched closely the pigment 502 spectral curve like other rhodopsin-possessing marine species. The ERG b-wave is as good an indicator of spectral sensitivity as the unmasked LRP that directly reflects the responsiveness of photoreceptors. Differences in spectral sensitivity were not revealed between dogfish preparations studied under a variety of conditions (isolated eyecup vs. detached retina; b-wave recording in fresh preparations vs. LRP measurements after low-temperature aging; dark vs. light adaptation). We developed a new model for spectral sensitivity data. [ABSTRACT FROM AUTHOR]

The polarization of hair cells from the end organs of the inner ear from the lesser spotted dogfish Scyliorhinus canicula from the order Carcharhiniforms (ground sharks) was studied using a scanning electron microscope (SEM), revealing arrays of hair cells with diverse orientations on each of the sensory epithelia. The greatest numbers of hair cells were found on the utricular epithelium and orientated on the horizontal plane, whilst the smallest number were found on the anterior macula neglecta and orientated on the vertical plane. Examination of the posterior macula neglecta revealed a dense profusion of c. 500 000 individual elongate structures, each resembling long microvilli, a finding not previously described in elasmobranch auditory physiology. [ABSTRACT FROM AUTHOR]

Abstract: Encased embryos of spotted dogfish Scyliorhinus canicula absorbed six radio-isotopes (241Am, 109Cd, 57Co, 134Cs, 54Mn and 65Zn) directly from seawater during short-term experimental exposure, demonstrating the permeability of the egg-case to these contaminants. Embryo to water concentration factors (CFs) ranged from 0.14 for 134Cs to 7.4 for 65Zn. The 65Zn and 57Co CFs increased exponentially with embryo length, whereas the CF for 109Cd declined with length. Among different components of the encased embryo the egg case was the major repository (69–99%) of all six radio-isotopes that were distributed throughout its wall. Egg-case CFs were as high as 103 for 57Co and 65Zn, making it the major source of gamma radiation exposure to the embryo and potentially of radio-isotopes for continued absorption by the embryo, following the uptake phase of the experiment. The patterns of uptake by the egg-case approximated linearity for most isotopes and loss rates were isotope-specific; egg-case biokinetics were not greatly affected by the viability of the contained embryo. Within the embryo initial data on radio isotopic distribution show that the skin is their major site of uptake, as previously demonstrated for juveniles. [Copyright &y& Elsevier]