Etmopterus Spinax Research Articles

Trophodynamics of a deep-sea demersal fish assemblage from the bathyal eastern Ionian Sea (Mediterranean Sea)

Daily food consumption of the eight dominant demersal fish species of the bathyal eastern Ionian Sea were determined from field data on four seasonal cruises (April 1999, July August 1999, November 1999 and February 2000). Daily ration (DR) estimates ranged from 0.198 to 4.273% WW/WW. Overall, DR estimates were independent of the model used, and they were comparable to the daily consumption of other deep-sea fauna (e.g. fish and crustaceans). Both sharks studied ( Galeus melastomus and Etmopterus spinax) exhibited the highest values of DRs, together with the macrourid Coelorhynchus coelorhynchus in August. Among osteichthyes, DR estimates were related (in a multi-linear regression model) to the nature of their diet (i.e. their trophic level deduced from δ 15N isotopic composition, the mean number of prey and trophic diversity). Thus, species feeding at a lower trophic level, ingesting a large number of prey items and with a very diversified diet had higher DR than species from higher trophic level and feeding fewer prey items. By season, the DR of species feeding mainly on mesopelagic prey ( Hoplostethus mediterraneus and Helicolenus dactylopterus) were higher in summer, while DR for benthos/suprabenthos feeders (i.e. C. coelorhynchus and Nezumia sclerorhynchus) were higher in spring. Higher food consumption coincides with maximum food availability, both among mesopelagic feeders (higher availability of euphausiids, Pasiphaea sivado and Sergestes arcticus in summer) and among Macrouridae (higher suprabenthos densities in spring). In a tentative estimate the energy intake deduced from diet (i.e. mean energy value of food ingested) was constant in all seasons for each species studied. Results for the energy intake also indicate higher energy intake in the diet of mesopelagic feeders than in the diet of benthic feeders. Overall results are discussed in relation to the deep-sea ecosystem structure and functioning.

Demersal assemblages and depth distribution of elasmobranchs from the continental shelf and slope off the Balearic Islands (western Mediterranean)

Abstract The analysis of 131 hauls from four bottom trawl fishing surveys carried out between depths of 46 and 1713 m in two different areas off the Balearic Islands yielded a total of 23 elasmobranch species belonging to eight families. Cluster analysis and multidimensional scaling (MDS) ordination were applied to detect zonation patterns and some ecological parameters (e.g. species richness, abundance and biomass, mean weight, diversity and evenness) were calculated for each assemblage. For each area, analysis of similitude (ANOSIM) and similarity percentage analysis (SIMPER) were also applied to detect differences between seasons and depths. For the most important species (Galeus melastomus, Scyliorhinus canicula, Centroscymnus coelolepis, Etmopterus spinax, Squalus blainvillei, Raja naevus, Raja asterias, Raja clavata, Raja miraletus and Raja oxyrhinchus), abundance and size distributions were analysed by depth.

The by-catch of sharks in the western Mediterranean (Balearic Islands) trawl fishery

The shark species, blackmouth catshark ( Galeus melastomus), velvet belly ( Etmopterus spinax) and coastal spotted dogfish ( Scyliorhinus canicula) are an important by-catch of the Balearic Islands (Western Mediterranean) trawl fishery. The catch compositions of the fishery taking these species is described and analysed in terms of landings and discards. Only two of these species are sufficiently abundant to be recorded in the landings (blackmouth catshark and spotted dogfish). The length compositions in terms of both landings and discards were analysed for these two species. Spotted dogfish catches reached similar proportions to those of the target species in the coastal fishery (red and striped red mullet) and in the shelf trawl fishery (European hake); whereas the catches of blackmouth catshark and velvet belly were a small proportion of the total catch in the slope fishery for red shrimp. The size range of the spotted dogfish was between 7 and 53 cm TL. Juveniles and adults were distributed throughout the whole area, although adults appeared to be more abundant in the coastal zone. The length distribution of blackmouth catshark showed a trend of increasing size with depth; the size range was between 9 and 63 cm TL. For both species, individuals smaller than 35 cm TL were usually discarded. Only 25% by number and 60% by weight of the total spotted dogfish catch was landed. For the total blackmouth catshark catch, the corresponding percentages were 10% by number and 35% by weight. The role of these species as indicators of fishing pressure was investigated, taking into account the differences between the two fishing zones sampled, one with a fleet of 24 trawlers and the other with only 4.

Metazoan parasites and food composition of juvenile Etmopterus spinax (L., 1758) (Dalatiidae, Squaliformes) from the Norwegian Deep.

A total of 37 juvenile Etmopterus spinax from the Norwegian Deep were examined for stomach contents and metazoan ecto- and endoparasites. These squaliform elasmobranchs were caught by benthopelagic net in May 2001 at a depth of 194-214 m. The euphausiid Meganyctiphanes norvegica and the teleost Maurolicus muelleri were the principal prey organisms. With increasing total length of E. spinax, the frequency of Meganyctiphanes norvegica prey decreased and that of M. muelleri increased. Seven different metazoan parasite species were found: adult Monogenea (2), larval and adult Cestoda (3), and larval Nematoda (2). The predominant parasites were an unidentified monocotylid monogenean and the cestode Aporhynchus norvegicus, with respective prevalences of infestation of 83.8% and 81.1%. The sites of infestation were the gills ( Squalonchocotyle spinacis, Monogenea), nasal cavities (Monocotylidae indet.), body cavity ( Lacistorhynchus tenuis, Cestoda), stomach wall and organs of the body cavity ( Anisakis simplex, Nematoda), and stomach and spiral valve ( A. norvegicus and Pseudophyllidea indet., Cestoda; Hysterothylacium aduncum, Nematoda). No other metazoan parasite taxa were found, and the musculature was free of parasites. Five new host and three new locality records were established. M. muelleri seems to be an important intermediate host for the endoparasitic nematodes which were found, with E. spinax serving as a paratenic host. E. spinax also serves as an intermediate host for the trypanorhynch cestode L. tenuis, and as the definitive host for the two monogeneans and the trypanorhynch A. norvegicus. The latter uses Meganyctiphanes norvegica as the second intermediate host in the Norwegian Deep. The relationship between the feeding ecology, habitat, and vagility of E. spinax and the resulting parasite fauna is discussed.

Hypophysial and extrahypophysial projections of the neurosecretory system of cartilaginous fishes: an immunocytochemical study using a polyclonal antibody against dogfish neurophysin.

Immunocytochemistry using antibodies against the neurohypophysial nonapeptides has given equivocal results regarding relevant aspects of the classical neurosecretory system of elasmobranchs. The lack of antibodies reacting with the elasmobranch neurophysins (Nps) has prevented the study of this neurosecretory system by Nps immunocytochemistry. This led us to purify Nps from Scyliorhinus canicula, and to use them to raise a polyclonal antibody. This antibody reacted strongly with the elasmobranch neurophysin neurons, revealing their most delicate and distant hypophysial and extrahypophysial projections. A detailed mapping of the neurosecretory system of five elasmobranch species (Etmopterus spinax, Squalus acanthias, Scyliorhinus canicula, Galeus melanostomus, Raja radiata) and one holocephalian species (Hydrolagus colliei) was performed. In elasmobranchs, the magnocellular neurophysin cells formed a distinct preoptic nucleus, whereas in Hydrolagus the immunoreactive cells were scattered. Distinct parvicellular neurophysin cells were present in the preoptic nucleus. In Raja the nucleus "O" contained parvicellular Nps-immunoreactive neurons. The findings at the pituitary level point to the possibility that neurophysin neurons, in addition to releasing nonapeptides into the systemic capillaries of the neural lobe, also participate in the regulation of the function of the rostral, medial and intermediate lobes of the adenohypophysis by a dual mechanism, i.e., a neurovascular pathway and a direct neural input. The extrahypophysial projections of the neurophysin neurons were highly developed to a degree not comparable to any other vertebrate group. The targets of these projections were located in the telencephalon, diencephalon and hindbrain. The evolutionary and functional implications of this phenomenon are discussed.

The ectoparasitic barnacle Anelasma (Cirripedia, Thoracica, Lepadomorpha) on the shark Centroscyllium nigrum (Chondrichthyes, Squalidae) from the Pacific sub-Antarctic

We report the occurrence of the ectoparasitic lepadomorph barnacle Anelasma sp. on the deep-sea squaloid shark Centroscyllium nigrum from the Pacific sub-Antarctic off southern Chile. Anelasma has previously been documented only from the northeast Atlantic on the squaloid shark Etmopterus spinax; this new record extends the known range of Anelasma into the Pacific Ocean and into the Southern Hemisphere, and documents a new host for this parasitic barnacle.

Metallothionein-like proteins in the livers of squaloid and carcharhinid sharks

Liver extracts from three species of shark ( Etmopterus spinax, Galeorhinus galeus, Scymnorhinus licha), were analysed using Differential Pulse Polarography. All three extracts gave significant polarographic responses, indicating the presence of cysteine containing proteins. On the basis of previous work, these proteins were considered to be metallothionein-like in nature. These results mark the first data on MT in natural populations of sharks and in mid- to deep-water species.

Differences in Force-Frequency Relationships and Calcium Dependency between Elasmobranch and Teleost Hearts

ABSTRACT Ventricle strips from little skate (Raja erinacea), spiny dogfish (Squalus acanthias), black dogfish (Etmopterus spinax), sea raven (Hemitripterus americanas), cod (Gadus morhua), hagfish (Myxine glutinosa) and white sturgeon (Acipenser transmontanus) were mounted for isometric force recording. Force development was assessed as a function of external calcium concentration and frequency of contraction. Post-rest potentiation was determined in skate and the teleost species to assess indirectly calcium storage capacities. Sea raven and cod preparations were also treated with ryanodine to assess the importance of calcium release from the sarcoplasmic reticulum. Ventricle strips from skate and black dogfish showed a five-fold increase in force development when external calcium was raised from a physiological to a saturating level. Force development by ventricle strips from other species tested increased by only about 50% over the same range of calcium concentration. For all elasmobranchs tested, an elevation in frequency of contraction of ventricle strips resulted first in an increase and subsequently in a decrease in force development. The apices of the curves were well within the physiological range of heart rates exhibited by these species. Preparations from teleosts showed only a decrease in force development when contraction frequency was elevated. Skate ventricle strips exhibited a very marked post-rest potentiation at 3 mmol 1−1 external calcium. This protocol is considered to reflect the importance of intracellular calcium stores in the beat-to-beat maintenance of contractility. Sea raven and cod ventricle strips did not show any major post-rest potentiation, suggesting that calcium storage in hearts of these species is minimal. Ryanodine treatment had no effect upon sea raven and cod heart preparations. This approach further implies that calcium release from sarcoplasmic reticulum is not critical in these species.

THE CELLULAR STRUCTURE OF LYMPHOMYELOID TISSUES IN CHIMAERA MONSTROSA (PISCES, HOLOCEPHALI).

The ultrastructure of the main lymphomyeloid organs of the holocephalan fish, Chimaera monstrosa, is presented. The thymus is well developed even in adults. It is densely packed with small and large lymphocytes, the former predominating. The ultrastructure of C. monstrosa's lymphocytes is similar to that of mammalian ones. The lymphocytes show intimate connections with large epithelial reticulocytes, which infiltrate the cytoplasm of the lymphocytes with long processes. The lymphomyeloid tissues around the orbit are mainly granulocytopoietic. Two types of granulocytes occur: eosinophilic and heterophilic. The latter is found in excess. The granulocytes are ultrastructurally similar to those of elasmobranchs such as Etmopterus spinax and have similar characteristic granules. In addition to granulocytes in various stages, lymphocytes, plasma cells, blast cells, and solitary macrophages are scattered throughout the tissue. The suprapalatal region also has a similar supply and variety of cells, but most heterophilic granulocytes have modified granules. In the spleen, erythrocytes in different developmental stages are common. This confirms earlier studies which suggested that the spleen functions primarily as an erythrocytopoietic organ.

Notes on Norwegian marine Amphipoda. 10. Scavengers and fish associates

The dominant group of carrion-eating amphipods in Norway are the Lysianassoidea; they play an important role as scavengers in Norwegian and arctic waters. A number of genera damage fish caught in nets and on long-lines; in Norway the most serious damage is done by Anonyx and Tmetonyx species. Tmetonyx cicada and the isopod Cirolana borealis have also regularly been found in Cod roe. Symbionts of living fish belong to the genera Lafystius, Normanion, Opisa and Trischizostoma. Lafystius and Normanion have low host specificity, Opisa eschrichtii is found on gadids and Halibut Hippoglossus hippoglossus and Trischizostoma raschi on the small shark Etmopterus spinax. Little is known on the biology of these species.

THE CELLULAR STRUCTURE OF THE LEYDIG ORGAN IN THE SHARK,ETMOPTERUS SPINAX(L.)

In Etmopterus spinax, a small deep water shark, the predominating lymphomyeloid tissue is the so called Leydig organ. This consists of bone marrow-like tissue situated between the muscularis and the mucosa of the esophagus. Examination by light and electron microscopy shows that the Leydig organ produces large numbers of granulocytes and lymphocytes. Two main types of granulocytes occur, tentatively called heterophilic and eosinophilic. The heterophilic cells may be subdivided into three types which differ in the ultrastructure of the granules. Cells structurally resembling mammalian plasma cells are common. The presence of these cells indicates that the tissue is part of the shark immune system.

Dopamine-β-hydroxylase activity in the axillary bodies, the heart and the splanchnic nerve in two elasmobranchs, Squalus acanthias and etmopterus spinax

1. The activity of dopamine-β-hydroxylase (DBH) was examined in tissues from Squalus acanthias and Etmopterus spinax using tyramine as substrate. 2. The activity of DBH in axillary bodies in Squalus was 19040 ± 240 nmol/g per hr and in Etmopeterus 6120 ± 245 nmol/g per hr. 3. DBH activity in nervous tissue, i.e. the splanchnic nerve (together with coeliac artery) was found to be 123 ± 41 nmol/g per hr in Squalus and 384 ± 62 nmol/g per hr in Etmopterus. 4. In Squalus heart DBH activity was undetectable, while Etmopterus heart had DBH activity both in atrium and ventricle, 40 ± 13 and 18 ± nmol/g per hr respectively. 5. A small amount of DBH activity was found in Squalus blood plasma, 2 ± 0.7 nmol/ml per hr. 6. The DBH activity gave high formation of octopamine in a wide temperature range from 24.5 to 32°C.

The myoglobin content in red, intermediate and white fibres of the swimming muscle sin three species of shark–a comparative study using high‐performance liquid chromatography

A high‐performance liquid chromatographic (HPLC) procedure is described for the determination of myoglobin in extracts of small samples of tissue from the three different fibre types in the swimming muscles of three species of sharks, Etmopterus spinax, Galeus melastomus and Scyliorhinus canicula. The method, which is based on the separation of myoglobin from haemoglobin from haemoglobin based on HPLC using a gel permeation chromatography column, has a detection limit of about 3 pmol myoglobin (Mb). In addition it has the added advantage of specific identification by its Soret band absorption and quantification. In all three species, the three fibre types of the muscle are completely separated and can be isolated at a high degree of purity. In red fibres the myoglobin content varied between 565 nmol mg−1 wet weight (Scyliorhinus) and 170 nmol mg−1 wet weight (Galeus). Intermediate fibres contained from 215 to 57, and white fibres from 11 to zero nmol mg−1 wet weight. The myoglobin content is closely correlated to the vascularization as well as to the amounts of mitochondria in the different fibre types.

Studies on the nature of the Z‐discs in skeletal muscle fibres of sharks, Etmopterus spinax L. and Galeus melastomus Rafinesque‐Schmaltz

The ultrastructural details of Z‐discs from red, intermediate, and white axial muscle fibres from the sharks Etmopterus spinax and Galeus melastomus are described. Red fibre Z‐discs contain the most amorphous matrix material, and are thicker (100–115 nm) than intermediate (85–88 nm) and white Z‐discs (75–80 nm). Four sets of oblique bars extend tangentially from each thin filament. In each set two bars are present, those of white fibres are close together (approximately 5 nm), while those of red fibres are separated by a distance of 15 nm. A model of shark Z‐disc structure is proposed. The denaturation (heat transition) temperatures of the muscle proteins were studied by differential scanning calorimetry (DSC). The heat transitions of collagen, actin, and myosin were identified; the actin heat transition temperature increased in the sequence red, intermediate, and white. The total protein pattern of red and white muscle were studied by SDS electrophoresis. A protein with a molecular weight of about 55000 may represent a Z‐disc protein.

Glycosidases in lymphomyeloid (hematopoietic) tissues of elasmobranch fish

Abstract 1. 1. High lysozyme and chitinase activities were found in Leydig's organ of Etmopterus spinax, Somniosus microcephalus and Torpedo nobiliana, in Leydig's and epigonal organs and spleen of Raja radiata, and in the epigonal organ of Rhinoptera bonasus. 2. 2. Strong chitinase activity with little or no lysozyme activity was noted in Leydig's and epigonal organs of Scyliorhinus canicula, and in the epigonal organ of Ginglymostoma cirratum and Heterodontus francisci. 3. 3. Very high β-N-acetylglucosaminidase activity was found in lymphomyeloid organs of all species investigated, and in the pancreas of Somniosus microcephalus. 4. 4. Thirteen other glycosidases were assayed in lymphomyeloid and digestive tissues of Ginglymostoma cirratum, Heterodontus francisci and Etmopterus spinax. Activities of α- d -mannosidase, β- d -galactosidase, β- d -N- acetylgalactosaminidase , β- d -glucuronidase and α- and β- d -glucosidase usually were higher in lymphomyeloid tissues than in digestive tissues.

Genome size of some selachian fishes

Abstract The nuclear DNA content of 23 chondrichthyan species (9 Squalomorphii, 11 Batoidea and 3 Galeomorphii) has been studied. Their genome size ranged from 5.4 pg/N in Raja clavata (Batoidea) to 32.3 pg in Etmopterus spinax (Squalomorphii). The lowest values so far recorded for selachians have been reported within the Batoidea, with a slight interspecific variability at the intrafamilial level. In contrast, the Squalomorphii displayed a high DNA content, with values mostly above those of all the other selachians hitherto assayed, and with a wide interspecific variability at the intrafamilial level. The results are discussed in relation to the data for other Chondrichthyes, and comparison is made with the genome size in other vertebrate classes.

Lysozyme, chitinase and exo-N-acetyl-?-D-glucosaminidase (NAGase) in lymphomyeloid tissue of marine fishes

Lymphomyeloid (haemopoietic) tissues produce or store blood cells — among these leucocytes rich in lysosomal enzymes. The thymus, unlike the other lymphomyeloid tissues found in fish, produces exclusively lymphocytes. The carbohydrate-hydrolysing enzymes lysozyme (EC 3.2.1.17), chitinase (EC 3.2.1.14) and exo-N-acetyl-β-D-glucosaminidase (NAGase; EC 3.2.1.30) were assayed in various lymphomyeloid tissues of the cartilaginous fish Chimaera monstrosa, Squalus acanthias, Etmopterus spinax and Raja radiata, and in the thymus of the marine teleost Lophius piscatorius. Lysozyme activity was high in the cranial lymphomyeloid tissue of C. monstrosa; in Leydig's organ (oesophageal lymphomyeloid tissue) and the spleen from E. spinax; and in Leydig's organ, the epigonal organ and the spleen from R. radiata. Little or no lysozyme activity was found in Leydig's organ and the epigonal organ of S. acanthias, or in the thymus of C. monstrosa, R. radiata and L. piscatorius. The pH optima for lysozyme activities lay between 4.8 and 5.4 when assayed photometrically. Chitinase was most active at pH 1 in Leydig's organ from R. radiata, and at pH 2.7 in the epigonal organ from S. acanthias. The chitinolytic activity in Leydig's organ of E. spinax may be due to lysozyme. The optimum for NAGase activity in Leydig's organ from R. radiata lay at pH 4.0, that from S. acanthias and E. spinax at pH 4.5. The role of the enzymes in the defense against microorganisms and parasites is discussed.

Chitinolytic enzymes in the digestive system of marine fishes

Chitinase, exo-N-acetyl-β-D-glycosaminidase (NAGase) and lysozyme activities were assayed in the digestive tract of 6 species of marine fishes: Myxine glutinosa (cyclostome), Chimaera monstrosa (holocephalan), Squalus acanthias, Etmopterus spinax, Raja radiata (elasmobranchs) and Coryphaenoides rupestris (teleost). Strong chitinase activity was found in the gastric mucosa of the elasmobranchs (S. acanthias, E. spinax and R. radiata) and the teleost (Coryphaenoides rupestris). A remarkably high chitinase activity occurred in the pancreas of the stomachless holocephalan fish Chimaera monstrosa. NAGase activity was strong in the digestive tract of all species. It could be concluded that marine fishes with diets consisting largely of chitinous invertebrates may display high chitinase and NAGase activities in their digestive system; however, only low chitinase activity was found in the intestine of the cyclostome Myxine glutinosa. Coryphaenoides rupestris gastric mucosa chitinase had one optimum activity at pH 1.25, whereas S. acanthias chitinase had two optima, at pH 1.6 and 3.6. The NAGase pH-activity curves from S. acanthias and R. radiata gastric mucosa displayed similar optima, at pH 4.5 and 4.25 respectively. Chimaera monstrosa pancreatic chitinase had a very strong optimum around pH 8 to 10, and one less strong at pH 3. These enzyme activities could not be separated by gel filtration or isoelectric focusing. The pI (isoelectric point) was approximately 4.9 for both enzymes. The molecular weight of the C. monstrosa pancreatic chitinase was estimated to be approximately 43 000. Lysozyme activity was absent or extremely weak in the material studied.

Ultrastructure of the different fibre types in axial muscles of the sharks Etmopterus spinax and Galeus melastomus.

Red, intermediate and white axial muscle fibres of the sharks Etmopterus spinax and Galeus melastomus were studied by electron microscopy and morphometry. The mitochondrial content is more than thirty percent in red, less than one percent in white, and up to fifteen percent in intermediate fibres. About one third of the mitochondria in red fibres are accumulated close to the sarcolemma. Red fibres contain much glycogen, present as rosettes (alpha particles). Intermediate fibres contain less glycogen (as beta particles). White fibres have scarcely any visible energy reserves. Red fibres contain slightly less (4-5%) of the sarcotubular system than the other fibre types (6-8%). In all fibre types, the terminal cisternae of the SR are regularly divided by clefts. Triads or dyads are generally positioned at the Z discs, but in Galeus white fibres two dyads may be present, one on each side of the Z disc. The morphology is discussed in relation to current views on the functions of different muscle fibre types.

Morphometric and autoradiographic studies on the growth of red and white axial muscle fibres in the shark Etmopterus spinax

The axial muscle growth of the shark Etmopterus spinax has been studied by means of morphometry, slide histology and autoradiography from radioactive thymidine and amino acids. Comparisons have been made between the red and white muscles fibres. While growing from 10 to 23 cm in length, the white muscle transverse sectional (ts) area increases 5.4 times, while the red area increases 3.7 times. The mean ts area of individual white fibres increases by 2.7, and the ts area of red fibres increases by 1.6. The number of white fibres does not increase significantly, while the red fibres increase slightly in number. Red fibres incorporate amino acids faster than the white fibres, and have a higher turnover rate. The myonuclei of the red fibres (satellite cell nuclei) incorporate thymidine more often than do those of white fibres, but the frequency of the satellite cells is similar in the two fibre types. Mitoses are extremely rare in the myonuclei. The nucleocytoplasmic ratio is higher in the red than in the white fibres.