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PubMedDate not supplied

Effects of endurance training in the leopard shark, Triakis semifasciata.

This study is the first to examine the effects of endurance training in an elasmobranch fish. Twenty-four leopard sharks (Triakis semifasciata) were divided randomly into three groups. Eight sharks were killed immediately, eight were forced to swim continuously for 6 wk against a current of 35 cm s-1 (60%-65% of maximal sustainable swimming speed), and eight were held for 6 wk in a tank without induced current. There were no changes due to training in maximal sustainable speed, oxygen consumption rates, percentage of the myotome composed of red and white muscle fibers, blood oxygen-carrying capacity, liver mass, liver lipid, glycogen, and protein concentrations, white muscle protein content, heart ventricle mass, or the specific activities of the enzymes citrate synthase, pyruvate kinase, and lactate dehydrogenase in the heart ventricle. In red myotomal muscle, citrate synthase activity increased 17% as a result of training, but there was no change in muscle fiber diameter. The greatest effects occurred in white myotomal muscle, in which a 34% increase in fiber diameter and a 36% increase in the activities of citrate synthase and lactate dehydrogenase occurred as a result of training. The conditioned fish also had significantly higher growth rates. The observed effects within the myotomal muscle may reflect the higher growth rates of the trained leopard sharks, or they may be a specific response to the increased energetic demands of the training activity, indicating characteristics that limit swimming performance in leopard sharks.

Analysis of Variance↗
PubMed1993

Protein evolution in different cellular environments: cytochrome b in sharks and mammals.

DNA sequences for the mitochondrial cytochrome b gene were determined for 13 species of sharks. Rates and patterns of amino acid replacement are compared for sharks and mammals. Absolute rates of cytochrome b evolution are six times slower in sharks than in mammals. Bivariate plots of the number of nonsynonymous and silent transversions are indistinguishable in the two groups, however, suggesting that the differences in amino acid replacement rates are due primarily to differences in DNA substitution rates. Patterns of amino acid replacement are also similar in the two groups. Conserved and variable regions occur in the same parts of the cytochrome b gene, and there is little evidence that the types of amino acid changes are significantly different between the groups. Similarity in the relative rates and patterns of protein change between the two groups prevails despite dramatic differences in the cellular environments of sharks and mammals. Poor penetrance of physiological differences through to rates of protein evolution provides support for the neutral theory and suggests that, for cytochrome b, patterns of evolution have been relatively constant throughout much of vertebrate history.

Amino Acid Sequence↗
PubMed2005

Sharks can detect changes in the geomagnetic field.

We used behavioural conditioning to demonstrate that sharks can detect changes in the geomagnetic field. Captive sharks were conditioned by pairing activation of an artificial magnetic field with presentation of food over a target. Conditioned sharks subsequently converged on the target when the artificial magnetic field was activated but no food reward was presented thereby demonstrating that they were able to sense the altered magnetic field. This strong response provides a robust behavioural assay that could be used to determine how sharks detect magnetic fields and to measure detection thresholds.

Animals↗
PubMed2005

Water-escape velocities in jumping blacktip sharks.

This paper describes the first determination of water-escape velocities in free-ranging sharks. Two approximations are used to estimate the final swimming speed at the moment of penetrating the water surface. Blacktip sharks were videotaped from below the surface and parameters were estimated by analysing the sequences frame by frame. Water-escape velocities averaged 6.3 ms(-1). These velocities for blacktip sharks seem accurate and are similar to estimates obtained for other shark species of similar size.

Animals↗
PubMed2006

The absence of sharks from abyssal regions of the world's oceans.

The oceanic abyss (depths greater than 3000 m), one of the largest environments on the planet, is characterized by absence of solar light, high pressures and remoteness from surface food supply necessitating special molecular, physiological, behavioural and ecological adaptations of organisms that live there. Sampling by trawl, baited hooks and cameras we show that the Chondrichthyes (sharks, rays and chimaeras) are absent from, or very rare in this region. Analysis of a global data set shows a trend of rapid disappearance of chondrichthyan species with depth when compared with bony fishes. Sharks, apparently well adapted to life at high pressures are conspicuous on slopes down to 2000 m including scavenging at food falls such as dead whales. We propose that they are excluded from the abyss by high-energy demand, including an oil-rich liver for buoyancy, which cannot be sustained in extreme oligotrophic conditions. Sharks are apparently confined to ca 30% of the total ocean and distribution of many species is fragmented around sea mounts, ocean ridges and ocean margins. All populations are therefore within reach of human fisheries, and there is no hidden reserve of chondrichthyan biomass or biodiversity in the deep sea. Sharks may be more vulnerable to over-exploitation than previously thought.

Animals↗
PubMed2006

Mode of attachment and lesions associated with trypanorhynch cestodes in the gastrointestinal tracts of two species of sharks collected from coastal waters of Borneo.

Lesions associated with two species of tapeworms within the digestive tract of wild-caught specimens of the bull shark, Carcharhinus leucas, and the sicklefin weasel shark, Hemigaleus microstoma, from Malaysian Borneo are described. Portions of the glandular stomach and pyloric gut with parasites were removed and fixed in 10% formalin buffered in sea water. Whole mounts, histological sections of tissues with and without worms in situ, and scanning electron microscopy images of detached worms were examined. Both species of cestodes belonged to the trypanorhynch family Tentaculariidae. Heteronybelinia estigmena was found in large numbers parasitizing the pyloric gut of C. leucas; an unidentified tentaculariid was found in relatively small numbers in both the glandular stomach and pyloric gut of H. microstoma. Both species burrowed their scoleces deeply in the mucosa and attached via hooked tentacles and unciniform microtriches of the scolex. The lesions induced by the parasites were marked in both sharks and ranged from acute necrotizing to chronic granulomatous gastroenteritis. Regenerative hyperplasia and intestinal metaplasia of gastric epithelium were also present. The severity and character of pathology was causally linked to the intensity of infection, the attachment mode of the parasites, and to the anatomophysiological relationships within the gut of the host shark.

Animals↗
PubMed2006

Worldwide phylogeography of the blacktip shark (Carcharhinus limbatus) inferred from mitochondrial DNA reveals isolation of western Atlantic populations coupled with recent Pacific dispersal.

Although many coastal shark species have widespread distributions, the genetic relatedness of worldwide populations has been examined for few species. The blacktip shark, (Carcharhinus limbatus), inhabits tropical and subtropical coastal waters throughout the world. In this study, we examined the genetic relationships of blacktip shark populations (n = 364 sharks) throughout the majority of the species' range using the entire mitochondrial control region (1067-1070 nucleotides). Two geographically distinct maternal lineages (western Atlantic, Gulf of Mexico, and Caribbean Sea clades, and eastern Atlantic, Indian, and Pacific Ocean clades) were identified and shallow population structure was detected throughout their geographic ranges. These findings indicate that a major population subdivision exists across the Atlantic Ocean, but not the Pacific Ocean. The historical dispersal of this widespread, coastal species may have been interrupted by the rise of the Isthmus of Panama. This scenario implies historical dispersal across the Pacific Ocean (supported by the recovery of the same common haplotype from the Philippines, Hawaii, and the Gulf of California reflecting recent/contemporary dispersal abilities) and an oceanic barrier to recent migration across the Atlantic. Genetic structure within the eastern Atlantic/Indo-Pacific (Phi(ST) = 0.612, P < 0.001) supports maternal philopatry throughout this area, expanding previous western Atlantic findings. Eastern Atlantic/Indo-Pacific C. limbatus control region haplotypes were paraphyletic to Carcharhinus tilstoni haplotypes in our maximum-parsimony analysis. The greater divergence of western Atlantic C. limbatus than C. tilstoni from eastern Atlantic/Indo-Pacific C. limbatus reflects the taxonomic uncertainty of western Atlantic C. limbatus.

Animal Migration↗
PubMed1998

Antibodies of sharks: revolution and evolution.

The combinatorial immune response is restricted to jawed vertebrates with cartilaginous fishes being the lowest extant species to have the mechanism for diversification and an extensive panoply of immunoglobulins, T-cell receptors and MHC products. Here, we review the molecular events of the "big bang" or rapid evolutionary appearance of the functionally complete combinatorial immune system coincident with the appearance of ancestral jawed vertebrates, suggesting that this event was catalyzed by horizontal transfer of DNA processing systems. We analyze the nature and extent of variable and constant domain diversity among the distinct immunoglobulin sets of carcharhine sharks focusing upon the lambda-like light chains and the mu and omega heavy chains. The detection and isolation of natural antibodies from the blood of unimmunized sharks illustrates a surprising range of recognition specificities and the existence of polyspecificity suggests that the antibody-forming system of sharks offers unique opportunities for studies of immunological regulation. Although the homologies between shark and mammalian immunoglobulins are unequivocal, major differences in segmental gene organization present challenges to our understanding of basic immunological phenomena such as clonal restriction.

Amino Acid Sequence↗
PubMed1988

Microradiographic study of demineralization of shark enamel in a human caries model.

The aim of the present study was to compare the resistance of fluoroapatite (shark enamel) and hydroxyapatite (human enamel) against a high caries challenge in a human in vivo model. Two samples of shark enamel and human enamel were each placed in removable appliances in six children and carried for 1 month and a plaque retentive device was placed over each enamel sample. The results showed that the mean total mineral loss (delta Z) was 1680 vol% micron in human enamel and 965 vol% micron in shark enamel. The corresponding mean values for lesion depth were 90 micron and 36 micron, respectively. It is concluded that even shark enamel containing 30,000 ppm F has a limited resistance against caries attacks.

Adolescent↗
PubMed2003

Collapse and conservation of shark populations in the Northwest Atlantic.

Overexploitation threatens the future of many large vertebrates. In the ocean, tunas and sea turtles are current conservation concerns because of this intense pressure. The status of most shark species, in contrast, remains uncertain. Using the largest data set in the Northwest Atlantic, we show rapid large declines in large coastal and oceanic shark populations. Scalloped hammerhead, white, and thresher sharks are each estimated to have declined by over 75% in the past 15 years. Closed-area models highlight priority areas for shark conservation, and the need to consider effort reallocation and site selection if marine reserves are to benefit multiple threatened species.

Animals↗
PubMed1967

Hydrocarbons in digestive tract and liver of a basking shark.

The hydrocarbons of zooplankton pass through the digestive tract of the basking shark without fractionation or structural modification. They are resorbed in the spiral valve and deposited in the liver. In contrast to unsaturated fatty acids, the olefinic hydrocarbons are not decreased in concentration. The hydrocarbon assemblage in the digestive tract and in the liver is indicative of the food sources and feeding grounds of the shark. Squalene, abundant in shark liver, occurs only in traces in zooplankton; phytane, if present at all, constitutes less than 0.005 percent of the hydrocarbons of zooplankton and of shark liver.

Alkanes↗
PubMed2002

Transepithelial organic anion transport by shark choroid plexus.

Spiny dogfish shark (Squalus acanthias) lateral and IV choroid plexuses (CPs) are ultrastructurally similar to the corresponding tissues of rat. However, shark IV CP is proportionally larger and easily accessible. Moreover, this epithelial sheet can be halved and studied in Ussing flux chambers. We have used confocal fluorescence microscopy and radiotracer techniques to characterize transepithelial transport of the organic anions (OAs) fluorescein (FL) and 2,4-dichlorophenoxyacetic acid (2,4-D), respectively, by shark CP. Lateral and IV CP accumulated 1 microM FL, with highest levels in the underlying extracellular spaces, intermediate levels in epithelial cells, and lowest levels in the medium. 2,4-D and probenecid inhibited FL accumulation in cells and extracellular spaces, suggesting that these substrates compete for common carriers. Unidirectional absorptive [cerebrospinal fluid (CSF)-to-blood] and secretory (blood-to-CSF) fluxes of 10 microM [(14)C]2,4-D were measured under short-circuited conditions in IV CP mounted in Ussing chambers. 2,4-D underwent net absorption, with an average flux ratio of 7. Probenecid, 2,4,5-trichlorophenoxyacetic acid, and 5-hydroxyindolacetic acid reduced net absorption, reversibly inhibiting unidirectional absorption, with no effect on secretion. Ouabain irreversibly reduced net 2,4-D absorption and cellular and extracellular accumulation of FL, suggesting energetic coupling of OA absorption to Na(+) transport. Collectively, these data indicate that shark CP actively removes OAs from CSF by a process that is specific and active.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1996

Immunocytochemical studies of the Na-K-Cl cotransporter of shark kidney.

The Na-K-Cl cotransporter (NKCC or BSC) has been described in numerous secretory and reabsorptive epithelia and is an important part of the mechanism of NaCl reabsorption in both the mammalian and elasmobranch kidneys. We have recently developed a panel of four monoclonal antibodies (MAbs) raised to the 195-kDa Na-K-Cl cotransport protein of the shark rectal gland (sNKCC1), which is expressed along the basolateral plasma membrane of secretory cells in this tissue (29). Here, we report immunologic studies of the Na-K-Cl cotransporter in the kidney of the dogfish shark Squalus acanthias. Western blot analysis of shark renal microsomes using MAbs J3, J7, and J25 identified proteins of approximately 195 and 150 kDa, whereas MAb J4 was not reactive. To define the cellular and subcellular distribution of the cotransport protein, immunofluorescence and immunoelectron microscopy studies were performed on fixed kidneys. Immunofluorescence microscopy on semithin (0.5-micron) cryosections demonstrated that MAbs J3, J7, and J25 intensely stained the apical plasma membrane of all distal tubule segments. Weak staining was also seen along the basolateral membrane of most distal nephrons. Immunoelectron microscopy confirmed this observation and showed that some of these segments were morphologically similar to diluting segments from other species. MAbs also reacted with the brush border and, to a lesser extent, the basolateral membrane of proximal tubules. This study supports the hypothesis that the lateral bundle zone of the elasmobranch kidney functions as a countercurrent exchanger and is consistent with the presence of multiple isoforms of the Na-K-Cl cotransporter in the shark kidney.

Animals↗
PubMed2003

Steady swimming muscle dynamics in the leopard shark Triakis semifasciata.

Patterns of red muscle strain and activation were examined at three positions along the body (0.42, 0.61 and 0.72 L, where L is total body length) and correlated with simultaneous measurements of midline kinematics during steady swimming (approx. 1.0 L s(-1)) in the leopard shark Triakis semifasciata. Analysis of lateral displacement along the body indicates that the leopard shark is a subcarangiform swimmer. Longitudinal variation in red muscle strain was observed with strain amplitudes ranging from +/-3.9% in the anterior, +/-6.6% in the mid, to +/-4.8% in the posterior body position. Strain was in-phase with local midline curvature. In addition, strain amplitude calculated from a bending beam model closely matched strain measured using sonomicrometry at all three body positions. There is a high degree of similarity in red muscle activation patterns along the body between the leopard shark and many fish species, in that the onset of activation occurs during muscle lengthening while offset occurs during muscle shortening. However, we found no significant longitudinal variation in the EMG/strain phase relationship and duty cycles, with onset of muscle activation occurring at 51.4-61.8 degrees and offset at 159.7-165.2 degrees (90 degrees is peak length). This consistent pattern of activation suggests that red muscle along the entire length of the body contributes to positive power production. Thus, sharks such as Triakis may have no regional specialization in red muscle function like that seen in many teleosts, which may indicate that the evolution of differential muscle function along the body occurred after the divergence of cartilaginous and bony fishes.

Animals↗
PubMed2005

The red muscle morphology of the thresher sharks (family Alopiidae).

A more medial and anterior position of the red aerobic myotomal muscle (RM) and the presence of a vascular counter-current heat exchange system provide the functional elements that facilitate regional RM endothermy in tunas, lamnid sharks and the common thresher shark (Alopias vulpinus). The convergent RM morphology among all species capable of RM endothermy suggests that RM position is a strong predictor of fish endothermic capacity. The present study investigated the comparative RM morphology of the other two thresher shark species (bigeye thresher, Alopias superciliosus, and the pelagic thresher, Alopias pelagicus), for which there is no information regarding their capacity for RM endothermy, and compared these data with published works on A. vulpinus. The digitization of transverse sections along the body of A. superciliosus and A. pelagicus enabled quantification of the relative amount of RM and the position and placement of the RM along the body. The RM in both A. superciliosus and A. pelagicus is positioned subcutaneously, along the lateral edges of the myotomes, and is distributed relatively evenly over the trunk of the body. The position of maximum RM area is at 50% fork length (FL) for A. superciliosus and at 75% FL for A. pelagicus. The amount of RM (mean +/- S.E.M.) is 2.31+/-0.11% and 3.01+/-0.10% in A. superciliosus and A. pelagicus, respectively. When compared with A. vulpinus, all three alopiid sharks have a similar amount of RM. However, A. superciliosus and A. pelagicus differ from A. vulpinus in that they do not possess the medial and anterior RM arrangement that would likely facilitate metabolic heat conservation (RM endothermy).

Animals↗
PubMed1997

Structural property and in vitro self-assembly of shark type I collagen.

The main structure of shark type I collagen is similar to that of land mammals, with a partial difference in amino acid sequence and post-translational modification. By static light scattering, the weight-average molecular weight of shark collagen (7.52 x 10(5)) suggests the presence of some aggregated molecules, oligomeric collagen. The self-assembly curve of shark collagen had a shorter lag phase and a longer growth phase than that of pig collagen. The optimum temperature and pH of shark collagen self-assembly is different from that of pig collagen.

Amino Acids↗
PubMed2002

Use of shark collagen for cell culture and zymography.

The uses of shark collagen as a matrix for cell culture and as a substrate for zymography were investigated. Fibroblasts were cultured on a gel matrix of shark type I collagen at 30 degrees C. The collagen gel had contracted by 4 days of incubation. Individual fibroblasts were visible against the transparent background of the contracted collagen as long, lean star-shaped cells. The matrix metalloproteinases (MMPs) from fibroblasts secreted from the medium more easily digested shark gelatin than pig gelatin. MMP-2, -9, and that of potential form were recognizable in the zymographic gel of shark gelatin.

Animals↗
PubMed2002

Ocular lesions associated with attachment of the copepod Ommatokoita elongata (Lernaeopodidae: Siphonostomatoida) to corneas of Pacific sleeper sharks Somniosus pacificus captured off Alaska in Prince William Sound.

Twenty eyes from 10 Pacific sleeper sharks Somniosus pacificus, infected with the copepod Ommatokoita elongata, were collected in Prince William Sound, Alaska, and the eyes of an additional 18 S. pacificus captured in the same area were inspected for copepods. Prevalence of infection by adult female O. elongata was 97% (n = 28); mean intensity of infection was 1.89 (+/-1SD = 0.32) adult female copepods per infected shark and 1.0 (+/- 1SD = 0.0) adult female copepods per infected eye. Five of the 20 collected eyes were infected by O. elongata chalimi, and 9 of 20 eyes had 1 to several remnants of bullae embedded in the cornea. Bullae were each associated with a corneal opacity, and anchoring plugs of chalimi were associated with pinpoint lesions in the cornea or conjunctiva. All eyes exhibited marked edema and erosion of the bulbar conjunctiva, and this torus-shaped lesion corresponded to each O. elongata adult female's presumed feeding and abrasion radius. Histological examinations revealed lesions in the anterior segment of eyes to be generally similar, but graded, in severity, and in all eyes they involved the conjunctiva, cornea, filtration angle, and iris. Epithelial lesions were characterized by corneal ulceration, dysplasia, hyperplasia, and heterophilic keratitis, and by ulcerative conjunctivitis accompanied by epithelial hyperplasia with rete peg formation. Disorganization of fibers, necrosis, mineralization, minimal heterophilic influx, and perilimbic neovascularization were associated with bullae in the corneal stroma. Within the limbus there was diffuse histiocytic and lymphocytic inflammation and marked lymphofollicular hyperplasia. Heterophilic and mononuclear anterior uveitis affecting the filtration angle and anterior surface of the iris was also observed in most eyes. One eye had a partial transcorneal prolapse of a ruptured lens, with degenerative changes in the ruptured lens and severe keratitis associated with the anchoring devices of an adult copepod and several chalimi. Fourteen eyes exhibited 1 to several, randomly distributed, small, round to irregular, corneal opacities or pits that were not associated with copepods, and it is likely that these opacities represented lesions associated with adult female or larval anchoring devices from past infections. The avascular cornea represents a niche that is somewhat shielded from host immune reactions, and this, and the fact that the general body surface of sleeper sharks is covered by tall and sharp placoid scales, may partially explain the corneal attachment of O. elongata adult females. It was concluded that O. elongata infections can lead to severe vision impairment in Pacific sleeper sharks but that these infections do not significantly debilitate hosts because they probably do not need to rely on acute vision for their survival.

Alaska↗