Squalus Acanthius Research Articles

3D Anatomy of the Jaw Muscles of the Spiny‐Tailed Dogfish ( Squalus acanthius )

New technologies are enabling anatomists to see inside animals to better understand the organization and function of the musculoskeletal system. Among the great transformations in vertebrate evolution is the acquisition and diversification of jaws and jaw musculature. Sharks are key species used in anatomy courses as well as research in organismal evolutionary biology where there is considerable diversity in cranial function and feeding behavior in the clade. Here, we use contrast imaging and 3D muscle fiber architecture visualization approaches to model and demonstrate the jaws and jaw muscles of the spinytailed dogfish (Sqaulus acanthius). A specimen was microCTed following immersion in an iodine-ethanol solution. Muscles and cartilages were segmented using Avizo. Muscle fascicles were then modeled using automated methods followed by manual noise reduction approaches. Colors of modeled fascicles were modeled to reflect orientations of muscles to reveal qualitative patterns in fiber organization. These segmented models of fascicles were then projected in quantitative space to show the orientations of muscle fascicles and moments of the quadratomandibularis, preorbitalis and levator hyomandibulae muscles among others. This 3D model will be shared with educators to include in comparative vertebrate anatomy courses. The results from the muscle architecture and mechanics data will be used to compare with other fishes and tetrapods as part of a growing study on the evolution of jaw muscles in vertebrates.

A real-time PCR assay to detect predation by spiny dogfish on Atlantic cod in the western North Atlantic Ocean.

Conventional observations show spiny dogfish (Squalus acanthius Linnaeus) rarely eat Atlantic cod (Gadus morhua Linnaeus; 0.02% of stomachs) in the northwestern Atlantic Ocean. Critics express concern that digestion may limit species‐level prey identification, and with recovery from overfishing, dogfish populations may be suppressing cod by competition or predation. This study applied a real‐time PCR TaqMan assay to identify cod in dogfish stomachs collected by cooperating fishing boats during normal trawling operations (May 2014–May 2015; Gulf of Maine, Georges Bank). Conventional methods observed 51 different prey taxa and nearly 1,600 individual prey items, but no cod were observed. Cod DNA was detected in 31 (10.5%) of the dogfish stomachs, with a higher percentage of these from the homogenate of amorphous, well‐digested prey and stomach fluids (20 stomachs or 65%) than from discrete animal tissues (11 stomachs or 35%). Re‐examination of photographs of these 11 tissue samples revealed one whole, partially digested fish that could be recognized in hindsight as cod. Cod DNA was observed in dogfish stomachs year round: in January (1 of 1 trip), February (1 of 1), May (1 of 3), June (0 of 1), July (3 of 4), August (1 of 2), and October (3 of 3). Although these data suggest higher interaction rates between dogfish and cod than previously observed, addressing the population consequences of this predator–prey relationship requires a robust sampling design, estimates of digestion rates by dogfish to account for complete degradation of DNA sequences, and consideration for dogfish scavenging during fishing operations.

Reducing elasmobranch bycatch: Laboratory investigation of rare earth metal and magnetic deterrents with spiny dogfish and Pacific halibut

Spiny dogfish ( Squalus acanthius) comprises a significant unwanted bycatch on demersal longlines set for halibut and cod in shelf waters of the east and west coasts of North America. In this laboratory study, attacks on baits were tested in the presence of two different rare earth materials (neodymium–iron–boride magnets and cerium mischmetal) believed to deter elasmobranch catch. Experiments were made with spiny dogfish and with Pacific halibut ( Hippoglossus stenolepis) in pairwise tests of the rare earth materials and inert metal controls. Dogfish attacked and consumed baits tested with cerium mischmetal at a lower frequency than controls. Times to attack the baits were significantly higher in the presence of mischmetal, as were numbers of approaches before first attack. The time differential between mischmetal and control treatments and the number of baits consumed converged with increasing food deprivation (1 h, 2 d, and 4 d), but treatment differences were always significant. Cerium mischmetal appeared to be irritating to dogfish and may disrupt their bait detection and orientation abilities. Magnets also appeared to irritate dogfish but provided no protection for baits in feeding trials. Pacific halibut showed no reaction whatsoever to the rare earth magnets or cerium mischmetal. Mischmetal, therefore, may be useful in reducing spiny dogfish bycatch in the halibut fishery. Disadvantages in using mischmetal in commercial operations are expense, hazardous nature, and relatively rapid hydrolysis in seawater.

Selective permeability barrier to urea in shark rectal gland

Elasmobranchs such as the dogfish shark Squalus acanthius achieve osmotic homeostasis by maintaining urea concentrations in the 300- to 400-mM range, thus offsetting to some degree ambient marine osmolalities of 900-1,000 mosmol/kgH(2)O. These creatures also maintain salt balance without losing urea by secreting a NaCl-rich (500 mM) and urea-poor (18 mM) fluid from the rectal gland that is isotonic with the plasma. The composition of the rectal gland fluid suggests that its epithelial cells are permeable to water and not to urea. Because previous work showed that lipid bilayers that permit water flux do not block flux of urea, we reasoned that the plasma membranes of rectal gland epithelial cells must either have aquaporin water channels or must have some selective barrier to urea flux. We therefore isolated apical and basolateral membranes from shark rectal glands and determined their permeabilities to water and urea. Apical membrane fractions were markedly enriched for Na-K-2Cl cotransporter, whereas basolateral membrane fractions were enriched for Na-K-ATPase. Basolateral membrane osmotic water permeability (P(f)) averaged 4.3 +/- 1.3 x 10(-3) cm/s, whereas urea permeability averaged 4.2 +/- 0.8 x 10(-7) cm/s. The activation energy for water flow averaged 16.4 kcal/mol. Apical membrane P(f) averaged 7.5 +/- 1.6 x 10(-4) cm/s, and urea permeability averaged 2.2 +/- 0.4 x 10(-7) cm/s, with an average activation energy for water flow of 18.6 kcal/mol. The relatively low water permeabilities and high activation energies argue strongly against water flux via aquaporins. Comparison of membrane water and urea permeabilities with those of artificial liposomes and other isolated biological membranes indicates that the basolateral membrane urea permeability is fivefold lower than would be anticipated for its water permeability. These results indicate that the rectal gland maintains a selective barrier to urea in its basolateral membranes.

Fishing and the Ground-Fish Assemblage Structure in the North-Western North Sea: An Analysis of Long-Term and Spatial Trends

This paper examines long-term changes in the structure and composition of the groundfish species assemblage in three regions of the north-western North Sea. Scottish fisheries research vessel data collected during the months July-September over the period 1929-53 are compared with more recent August groundfish survey data covering the period 1980-93. Trends in the whole groundfish assemblage, and in a subset of the assemblage that is not targeted by commercial fisheries, are described. Long-term differences in species assemblage were subtle, and were most apparent in the dominance structure. Species diversity in the whole groundfish assemblage was marginally greater in the period 1929-53, but no difference was apparent within the non-target species assemblage. For the whole groundfish assemblage, diversity was greatest in the inshore region and least in the offshore area, but there was no obvious spatial gradient for the non-target species assemblage. Multivariate analyses indicated long-term changes and between-area differences in the species composition for both the whole groundfish assemblage and the non-target species subset. More detailed examination of the data revealed that the long-term changes resulted from relatively small and subtle differences in the relative abundance of rarer species, such as grey gurnard Eutrigla gurnardus (L.) and spur-dog Squalus acanthius L.. In contrast, changes in the relative abundance of the more common species, such as Norway pout Trisopterus esmarkii (Nilsson) and whiting Merlangius merlangus (L.), explained much of the between-area variation. Examination of species aggregated length-frequency distributions suggested that by the 1980s there had been a shift towards assemblages in which smaller fish were more highly represented. This was only apparent, however, in the whole groundfish species assemblage ; the length-frequency distributions of non-targeted species were almost identical in the two time periods. Overall, the results suggest that, although differences in the structure of the whole fish assemblage can be detected, the non-target groundfish assemblage appears to have remained relatively unchanged, despite a century of intensive fishing activity.

Refined crystal structure of dogfish M 4 apo-lactate dehydrogenase

The crystal structure of M 4 apo-lactate dehydrogenase from the spiny dogfish ( Squalus acanthius) was initially refined by a constrained-restrained, and subsequently restrained, least-squares technique. The final structure contained 286 water molecules and two sulfate ions per subunit and gave an R-factor of 0.202 for difraction data between 8.0 and 2.0 Å resolution. The upper limit for the co-ordinate accuracy of the atoms was estimated to be 0.25 Å. The elements of secondary structure of the refined protein have not changed from those described previously, except for the appearance of a one-and-a-half turn 3 10 helix immediately after βJ. There is also a short segment of 3 10 helix between βC and βD in the part of the chain that connects the two βαβαβ units of the six-stranded parallel sheet (residues Tyr83 to Ala87). Examination of the interactions among the different elements of secondary structure by means of a surface accessibility algorithm supports the four structural clusters in the subunit. The first of the two sulfate ions is in the active site and occupies a cavity near the essential His195. Its nearest protein ligands are Arg171, Aspl68 and Asn140. The second sulfate ion is located near the P-axis subunit interface. It is liganded by His188 and Arg173. These two residues are conserved in bacterial lactate dehydrogenase and form part of the fructose 1,6-bisphosphate effector binding site. Two other data sets in which one (collected at pH 7.8) or both (collected at pH 6.0) sulfate ions were replaced by citrate ions were also analyzed. Five cycles of refinement with respect to the pH 6.0 data (25 to 2.8 Å resolution) resulted in an R value of 0.191. Only water molecules occupy the subunit boundary anion binding site at pH 7.8. The amino acid sequence was found to be in poor agreement with (2 F obs − F calc) electron density maps for the peptide between residues 207 and 211. The original sequence WNALKE was replaced by NVASIK. The essential His195 is hydrogen bonded to Asp168 on one side and Asn140 on the other. The latter residue is part of a turn that contains the only cis peptide bond of the structure at Pro141. The “flexible loop” (residues 97 to 123), which folds down over the active center in ternary complexes of the enzyme with substrate and coenzyme, has a well-defined structure. Analysis of the environment of Tyr237 suggests how its chemical modification inhibits the enzyme.

Isolation and partial sequence of elasmobranch VIP

We have used a combination of gel filtration, ion exchange chromatography and reversed-phase HPLC to isolate and characterize a VIP-related peptide from the gut of the elasmobranch Scyliorhinus canicula. The N-terminal decapeptide of the Scyliorhinus material was identical with that of porcine VIP. However, Scyliorhinus VIP did not cross react with antisera specific for the C-terminus of porcine VIP. Like porcine VIP, Scyliorhinus VIP was a potent stimulant of exocrine pancreatic secretion in the turkey, but the response to Scyliorhinus VIP had a shorter duration. VIP from a second elasmobranch, Squalus acanthius was partially purified, and had biological and immunochemical properties similar to those of Scyliorhinus VIP. The results indicate that elasmobranch VIP is identical to porcine VIP at its N-terminus, but differs at the C-terminus. These structural differences may influence the rate of metabolism of the peptide.

Purification and characterisation of VIP from two species of dogfish

Acid extracts of intestine from the dogfish Scyliorhinus canicula and Squalus acanthius were purified by gel filtration, ion exchange chromatography, and reversed-phase HPLC. In radioimmunoassays, VIP-like material from both species of dogfish cross reacted with N-terminal, but not C-terminal antisera. Like porcine VIP, both Scyliorhinus and Squalus VIP were stimulants of exocrine pancreatic secretion in the turkey. The time course of the responses to dogfish VIP were, however, different from that seen with porcine VIP. The present study has developed methods for the isolation of VIP-like peptides from elasmobranchs and has demonstrated that elasmobranch VIP differs from Porcine VIP in the C-terminal region, and that these differences may affect biological activity.

Purification and characterization of pancreatic colipase from the dogfish ( Squalus acanthius)

Pure colipase from dogfish ( Squalus acanthius) was obtained from an extract of pancreatic gland. It has a high isoelectric point (10.2) and the molecular weight was calculated to be 9108–9383. The N-terminal sequence was shown to be Gly-Leu-Phe-Leu-Asn-Leu-Ser-Ala-Gly-Glu-Leu-Cys-Val-Gly-Ser-Phe-Gln-Cys-Lys-Ser-Ser-Cys-Cys-Gln-Arg-Glu-Thr-Gly-Leu-Ser-Leu-Ala-Arg-Cys-Ala-. This sequence shows great homology with colipases from man, horse, pig and hen. There were indications of the existence of a proform of dogfish colipase. The propeptide was found to be Ala-Pro-Glu-Arg.

Evolutionary studies on pancreatic colipase

In this evolutionary study the following criteria have been used to prove the existence of colipase: 1. It restores the activity of human and porcine pancreatic lipase inhibited by bile salt. 2. It cross-reacts with antisera to human and porcine colipases. 3. Its restoration of lipase activity, inhibited by bile salt, in the tributyrin assay system, is prevented by antiserum to colipase. 4. It is a heat-stable, low-molecular-weight protein (molecular weight about 10 000 by gel-filtration). The occurrence of colipase has been verified in the exocrine pancreatic cells from hagfish ( Myxine glutinosa), ratfish ( Chimaera monstrosa), rayfish ( Raja radiata), Greenland shark ( Somnius microcephalus) and dogfish ( Squalus acanthius). No colipase activity could be found in the gastric juice of crayfish ( Pacifastacus leniusculus). These results indicate that colipase envolved in the vertebrates before the organized exocrine pancreatic gland and occurred simultaneously with the bile salts/bile alcohols.

Aminoacid sequence of dogfish M4 lactate dehydrogenase.

About 80% of the aminoacid sequence of dogfish (Squalus acanthius) M(4) lactate dehydrogenase (EC 1.1.1.27) has been elucidated. Several sequence homologies with peptides from pig H(4) and pig M(4) lactate dehydrogenase are identified. Histidine 195 is homologous to the essential histidine residue in pig H(4) lactate dehydrogenase. Similarities in the sequence around the "essential" cysteine residue of lactate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, and yeast and liver alcohol dehydrogenase are delineated.

Structural constraints of possible mechanisms of lactate dehydrogenase as shown by high resolution studies of the apoenzyme and a variety of enzyme complexes.

In vertebrates, the NAD+-dependent enzyme lactate dehydrogenase (LDH) (EC 1.1.1.27) is a tetramer (mol wt 140,000) which catalyzes the interconversion of l(+) lactate and pyruvate. Two subunit types predominate, the M type in skeletal muscle and the H type in heart tissue. The subject of this study is the M4 isoenzyme from dogfish (Squalus acanthius).

On the mode of breeding of the ovo-viviparous shark, and on the aëration of the fætal blood in different classes of animals

With a view to understanding more fully the structure of the Squalus maximus, of which Mr. Home has lately published an account, he has examined with attention that of the Squalus acanthius, which appears to resemble it closely in its internal structure, and has the advantage of being very easily obtained upon the Sussex coast, where it is very common. After describing minutely the external organs of generation in both male and female, the author traces the progress of the ovaria from the time that the yolks are no larger than peas, till they become as large as walnuts, when they pass into the oviduct. The number of yolks differs in different fish; and even in the same fish Mr. H. has seen five yolks in one ovarium and only two in the other. The oviducts then enlarge, and become exceedingly extended, and divided by contraction of its coats into three cavities, the last of which is ten inches in length, and is that in which the eggs are retained till the young fishes are formed, and capable of taking care of themselves. The eggs, however, are not loose as in the oviducts of birds, but are grouped together to the number of three, four, or five, in membranous bags, containing a transparent jelly, in which the young fish swims about after it is formed, with the yolk attached to its belly by a long chord, consisting of blood-vessels. If the bag be torn and the fish taken out and put into water with its yolk attached to it, it swims about; but if the vessels of the chord are wounded, it dies immediately.

XII. On the mode of breeding of the oviviviparous shark, and on the aeration of the fœtal blood in different classes of animals

That some of the shark tribe do not lay their eggs, but hatch them within the body, and that others lay them in the same manner as the skate, has long been known; but nothing seems to have been accurately made out upon either of these subjects, I am therefore induced to lay before the Society the following observations. In my examination of the squalus maximus, an account of which is published, I found that it closely resembled in its in­ternal structure, the squalus acanthius of Linnaeus, a fish common on the Sussex coast, which made me pay particular attention to the anatomy of all the parts of this species of dogfish.