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Members of the Chondrichthyes (Elasmobranchii and Holocephali) are distinguished by their largely cartilaginous endoskeletons, which comprise an uncalcified core overlain by a mineralized layer; in the Elasmobranchii (sharks, skates, rays) most of this mineralization takes the form of calcified polygonal tiles known as tesserae. In recent years, these skeletal tissues have been described in ever increasing detail in sharks and rays, but those of Holocephali (chimaeroids) have been less well-studied, with conflicting accounts as to whether or not tesserae are present. During embryonic ontogeny in holocephalans, cervical vertebrae fuse to form a structure called the synarcual. The synarcual mineralizes early and progressively, anteroposteriorly and dorsoventrally, and therefore presents a good skeletal structure in which to observe mineralized tissues in this group. Here, we describe the development and mineralization of the synarcual in an adult and stage 36 elephant shark embryo (Callorhinchus milii). Small, discrete, but irregular blocks of cortical mineralization are present in stage 36, similar to what has been described recently in embryos of other chimaeroid taxa such as Hydrolagus, while in Callorhinchus adults, the blocks of mineralization are more irregular, but remain small. This differs from fossil members of the holocephalan crown group (Edaphodon), as well as from stem group holocephalans (e.g., Symmorida, Helodus, Iniopterygiformes), where tesserae are notably larger than in Callorhinchus and show similarities to elasmobranch tesserae, for example with respect to polygonal shape.

There is a need to better understand the survivorship of discarded fishes, both for commercial stocks and species of conservation concern. Within European waters, the landing obligations that are currently being phased in as part of the European Union's reformed common fisheries policy means that an increasing number of fish stocks, with certain exceptions, should not be discarded unless it can be demonstrated that there is a high probability of survival. This study reviews the various approaches that have been used to examine the discard survival of elasmobranchs, both in terms of at-vessel mortality (AVM) and post-release mortality (PRM), with relevant findings summarized for both the main types of fishing gear used and by taxonomic group. Discard survival varies with a range of biological attributes (species, size, sex and mode of gill ventilation) as well as the range of factors associated with capture (e.g. gear type, soak time, catch mass and composition, handling practices and the degree of exposure to air and any associated change in ambient temperature). In general, demersal species with buccal-pump ventilation have a higher survival than obligate ram ventilators. Several studies have indicated that females may have a higher survival than males. Certain taxa (including hammerhead sharks Sphyrna spp. and thresher sharks Alopias spp.) may be particularly prone to higher rates of mortality when caught.

There is a need to better understand the survivorship of discarded fishes, both for commercial stocks and species of conservation concern. Within European waters, the landing obligations that are currently being phased in as part of the European Union's reformed common fisheries policy means that an increasing number of fish stocks, with certain exceptions, should not be discarded unless it can be demonstrated that there is a high probability of survival. This study reviews the various approaches that have been used to examine the discard survival of elasmobranchs, both in terms of at-vessel mortality (AVM) and post-release mortality (PRM), with relevant findings summarized for both the main types of fishing gear used and by taxonomic group. Discard survival varies with a range of biological attributes (species, size, sex and mode of gill ventilation) as well as the range of factors associated with capture (e.g. gear type, soak time, catch mass and composition, handling practices and the degree of exposure to air and any associated change in ambient temperature). In general, demersal species with buccal-pump ventilation have a higher survival than obligate ram ventilators. Several studies have indicated that females may have a higher survival than males. Certain taxa (including hammerhead sharks Sphyrna spp. and thresher sharks Alopias spp.) may be particularly prone to higher rates of mortality when caught.

There is a need to better understand the survivorship of discarded fishes, both for commercial stocks and species of conservation concern. Within European waters, the landing obligations that are currently being phased in as part of the European Union's reformed common fisheries policy means that an increasing number of fish stocks, with certain exceptions, should not be discarded unless it can be demonstrated that there is a high probability of survival. This study reviews the various approaches that have been used to examine the discard survival of elasmobranchs, both in terms of at-vessel mortality (AVM) and post-release mortality (PRM), with relevant findings summarized for both the main types of fishing gear used and by taxonomic group. Discard survival varies with a range of biological attributes (species, size, sex and mode of gill ventilation) as well as the range of factors associated with capture (e.g. gear type, soak time, catch mass and composition, handling practices and the degree of exposure to air and any associated change in ambient temperature). In general, demersal species with buccal-pump ventilation have a higher survival than obligate ram ventilators. Several studies have indicated that females may have a higher survival than males. Certain taxa (including hammerhead sharks Sphyrna spp. and thresher sharks Alopias spp.) may be particularly prone to higher rates of mortality when caught.

Marine cartilaginous fish retain a high concentration of urea to maintain the plasma slightly hyperosmotic to the surrounding seawater. In adult fish, urea is produced by hepatic and extrahepatic ornithine urea cycles (OUCs). However, little is known about the urea retention mechanism in developing cartilaginous fish embryos. In order to address the question as to the mechanism of urea-based osmoregulation in developing embryos, the present study examined the gene expression profiles of OUC enzymes in oviparous holocephalan elephant fish (Callorhinchus milii) embryos. We found that the yolk sac membrane (YSM) makes an important contribution to the ureosmotic strategy of the early embryonic period. The expression of OUC enzyme genes was detectable in the embryonic body from at least stage 28, and increased markedly during development to hatching, which is most probably due to growth of the liver. During the early developmental period, however, the expression of OUC enzyme genes was not prominent in the embryonic body. Meanwhile, we found that the mRNA expression of OUC enzymes was detected in the extra-embryonic YSM; the mRNA expression of cmcpsIII in the YSM was much higher than that in the embryonic body during stages 28-31. Significant levels of enzyme activity and the existence of mitochondrial-type cmgs1 transcripts in the YSM supported the mRNA findings. We also found that the cmcpsIII transcript is localized in the vascularized inner layer of the YSM. Taken together, our findings demonstrate for the first time that the YSM is involved in urea-based osmoregulation during the early to mid phase of development in oviparous cartilaginous fish.

The cloning of melanocortin (MC) receptors in distant species has provided us tools to get insight in how the ligand–receptors interactions in the MC system have evolved. We have however lacked studies on pharmacology of native ancient melanocortin peptides at the ancient MC receptors. In this paper we synthesized melanocortin peptides from both the sea lamprey (Petromyzon marinus) and spiny dogfish (Squalus acanthias) and tested them on the MC3 and MC4 receptors from spiny dogfish. The results show that both the dogfish and lamprey ACTH peptides have similar or higher affinity than the dogfish α-, β- and γ-MSH peptides to the dogfish MC3 and MC4 receptors. Moreover, both the dogfish and lamprey ACTH peptides have more than 10-fold higher affinity than α-MSH to the dogfish MC4 receptor. We also show that dogfish δ-MSH is able to bind to MC receptors and its potency is higher than of dogfish β-MSH, which is considered to be its precursor. Our results provide the first evidence that native ACTH ligands from dogfish and lamprey have a preference above native MSH peptides to ancient version of the MC3 and MC4 receptors. This further strengthens the hypotheses that the ligand contributing to the first version of the melanocortin ligand-receptor system resembled ACTH.

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.

Scotopic electroretinogram of dogfish shark (Scylliorhinus canicula) and eel (Anguilla anguilla) is characterized by a negative off-response, changing in sign under photopic condition. It increased under the effect of increased background illumination, but its amplitude never exceeded that of the b-wave. On the other hand, dark-adapted electroretinograms of two perch-like species, perch (Perca fluviatilis) and painted comber (Serranus scriba), exhibited a positive off-wave, exceeding the b-wave amplitude under bright photopic conditions.

In this paper we present the first results on growth of dogfish (Scyliorhinus canicula L.) obtained from size frequency distributions collected during bottom trawl surveys and from 19 recaptures to date from 2 153 tagged individuals. The surveys belong to a series carried out in autumn in the Cantabrian Sea by the Institute Espanol de Oceanografia (1983-1995). The estimated parameters from the von Bertalanffy equation applying the Bhattacharya, Gulland and Holt and Ford-Walford methods were K of around 0.09-0.13, and a maximum length close to 89-98 cm. In addition, based on ten recoveries with reliable data of location we assume a priori that this species does not move long distances in the area of study, Les premiers résultats sur la croissance de la petite roussette (Scyliorhinus canicula L.) proviennent de la répartition des tailles de 2 153 individus marqués, après chalutage et 19 recaptures. Les campagnes ont été effectuées en automne (1983–1995) dans la mer Cantabrique par l'Institut Espagnol d'Océanographie. Les méthodes de Batthacharya, Gulland-Holt et Ford-Walford, appliquées à l'équation de von Bertalanffy, donnent des valeurs de K de l'ordre de 0.09-0.13 et une longueur maximale de 89–98 cm. Les positions fiables d'une dizaine de recaptures indiquent que l'espèce n'effectue pas de grands déplacements dans la région étudiée.

In this paper we present the first results on growth of dogfish (Scyliorhinus canicula L.) obtained from size frequency distributions collected during bottom trawl surveys and from 19 recaptures to date from 2 153 tagged individuals. The surveys belong to a series carried out in autumn in the Cantabrian Sea by the Institute Espanol de Oceanografia (1983-1995). The estimated parameters from the von Bertalanffy equation applying the Bhattacharya, Gulland and Holt and Ford-Walford methods were K of around 0.09-0.13, and a maximum length close to 89-98 cm. In addition, based on ten recoveries with reliable data of location we assume a priori that this species does not move long distances in the area of study, Les premiers résultats sur la croissance de la petite roussette (Scyliorhinus canicula L.) proviennent de la répartition des tailles de 2 153 individus marqués, après chalutage et 19 recaptures. Les campagnes ont été effectuées en automne (1983–1995) dans la mer Cantabrique par l'Institut Espagnol d'Océanographie. Les méthodes de Batthacharya, Gulland-Holt et Ford-Walford, appliquées à l'équation de von Bertalanffy, donnent des valeurs de K de l'ordre de 0.09-0.13 et une longueur maximale de 89–98 cm. Les positions fiables d'une dizaine de recaptures indiquent que l'espèce n'effectue pas de grands déplacements dans la région étudiée.

In this paper we present the first results on growth of dogfish (Scyliorhinus canicula L.) obtained from size frequency distributions collected during bottom trawl surveys and from 19 recaptures to date from 2 153 tagged individuals. The surveys belong to a series carried out in autumn in the Cantabrian Sea by the Institute Espanol de Oceanografia (1983-1995). The estimated parameters from the von Bertalanffy equation applying the Bhattacharya, Gulland and Holt and Ford-Walford methods were K of around 0.09-0.13, and a maximum length close to 89-98 cm. In addition, based on ten recoveries with reliable data of location we assume a priori that this species does not move long distances in the area of study, Les premiers résultats sur la croissance de la petite roussette (Scyliorhinus canicula L.) proviennent de la répartition des tailles de 2 153 individus marqués, après chalutage et 19 recaptures. Les campagnes ont été effectuées en automne (1983–1995) dans la mer Cantabrique par l'Institut Espagnol d'Océanographie. Les méthodes de Batthacharya, Gulland-Holt et Ford-Walford, appliquées à l'équation de von Bertalanffy, donnent des valeurs de K de l'ordre de 0.09-0.13 et une longueur maximale de 89–98 cm. Les positions fiables d'une dizaine de recaptures indiquent que l'espèce n'effectue pas de grands déplacements dans la région étudiée.

The blue whiting is the most important demersal species caught by the Spanish trawler fleet in the southern Bay of Biscay. Lesser spotted dogfish are not a commercial by-catch, and are discarded immediately after sorting. During 1994 the contents of 1094 dogfish stomachs were analysed. The results show that lesser spotted dogfish with a total length of >17 cm eat blue whiting throughout the year. The length range of blue whiting found in lesser spotted dogfish stomachs was similar to the length range discarded by the fishery. Blue whiting account for 20% of the stomach volume in lesser spotted dogfish 30–50 cm long. From the state of digestion of blue whiting prey, and the comparative analysis of the size distributions of blue whiting in lesser spotted dogfish stomachs and in the fishery, it appears that many of these blue whiting are discards, consumed when already dead or damaged. The impact of this supplementary food on lesser spotted dogfish abundance is discussed.

Blue whiting is the most important demersal species caught, in landed biomass as well as in discarded biomass, by the trawl fleet in the South part of the Gulf of Biscay. Dogfish' is not commercial by-catch and it is discarded inmediately after sorting. During 1994 were accomplished analysis of 1094 stomach contents of dogfish caught in commercial ships working in a discard sampling program and a cruise research. The results reveal that from 17 cm, this especie depredates on blue whiting along all the year. The length ranges found in the stornach contents (6-31 cm) is similar to the length ranges discarded in the fishery (7-39 cm). The average quantity of blue whiting in stomachs of dogfish between 40 and 60 cm constitutes the 25% of the stomachs volume. The state of digestion in which is found the blue whiting prey, and the comparative analysis of the size distributions of blue whiting of the stomachs and the one of the fishery, presuppose that the blue whiting consumed is dead material originated from discard. Finally it is discussed the importance that this supplementary material can have in dogfish abundance.

President Roosevelt congratulates Masters George W. Powers and Frank K. McCourt on their catch of fish.