The Rectal Gland of the Shark: The Road to Understanding the Mechanism and Regulation of Transepithelial Chloride Transport.

Pictured, described, and speculated on, for close to 400 years, the function of the rectal gland of elasmobranchs remained unknown. In the late 1950s, Burger discovered that the rectal gland of Squalus acanthias secreted an almost pure solution of sodium chloride, isosmotic with blood, which could be stimulated by volume expansion of the fish. Twenty five years later, Stoff discovered that the secretion of the gland was mediated by adenyl cyclase. Studies since then have shown that vasoactive intestinal peptide (VIP) is the neurotransmitter responsible for activating adenyl cyclase; however, the amount of circulating VIP does not change in response to volume expansion. The humoral factor involved in activating the secretion of the gland is C-type natriuretic peptide, secreted from the heart in response to volume expansion. C-type natriuretic peptide circulates to the gland where it stimulates the release of VIP from nerves within the gland, but it also has a direct effect, independent of VIP. Sodium, potassium, and chloride are required for the gland to secrete, and the secretion of the gland is inhibited by ouabain or furosemide. The current model for the secretion of chloride was developed from this information. Basolateral NaKATPase maintains a low intracellular concentration of sodium, which establishes the large electrochemical gradient for sodium directed into the cell. Sodium moves from the blood into the cell (together with potassium and chloride) down this electrochemical gradient, through a coupled sodium, potassium, and two chloride cotransporter (NKCC1). On activation, chloride moves from the cell into the gland lumen, down its electrical gradient through apical cystic fibrosis transmembrane regulator. The fall in intracellular chloride leads to the phosphorylation and activation of NKCC1 that allows more chloride into the cell. Transepithelial sodium secretion into the lumen is driven by an electrical gradient through a paracellular pathway. The aim of this review was to examine the history of the origin of this model for the transport of chloride and suggest that it is applicable to many epithelia that transport chloride, both in resorptive and secretory directions.

Pharmacokinetics of robenacoxib after a single intramuscular dose in smooth dogfish (Mustelus canis).

OBJECTIVE: To determine the pharmacokinetics of robenacoxib after a single intramuscular dose (4.0 mg/kg) in smooth dogfish (Mustelus canis). ANIMALS: 8 healthy adult male smooth dogfish in human care within the same habitat. METHODS: All sharks received a single intramuscular dose of robenacoxib (4.0 mg/kg) in the right caudolateral epaxial musculature. Blood samples were collected under manual restraint from the ventral tail vessel at 30 minutes, 1 hour, 2 hours, 4 hours, 8 hours, and 24 hours after drug administration. Plasma drug concentrations were determined by HPLC followed by noncompartmental pharmacokinetic analysis of the data. RESULTS: A maximum plasma concentration of 1.24 µg/mL was reached at a mean time of 30 minutes following robenacoxib administration with a plasma elimination half-life of 3.79 hours. Plasma concentrations did not fall below the lower limit of quantification (0.1 µg/mL) at the time points sampled in this study. CLINICAL RELEVANCE: Intramuscular administration of a single dose (4.0 mg/kg) of robenacoxib in smooth dogfish resulted in rapid absorption to a maximum concentration at approximately 30 minutes after administration and persisted above levels considered to be therapeutic in domestic species for at least 8 hours.

Using 15N to determine the metabolic fate of dietary nitrogen in North Pacific spiny dogfish (Squalus acanthias suckleyi).

Marine elasmobranchs are ureosmotic, retaining large concentrations of urea to balance their internal osmotic pressure with that of the external marine environment. The synthesis of urea requires the intake of exogenous nitrogen to maintain whole-body nitrogen balance and satisfy obligatory osmoregulatory and somatic processes. We hypothesized that dietary nitrogen may be directed toward the synthesis of specific nitrogenous molecules in post-fed animals; specifically, we predicted the preferential accumulation and retention of labelled nitrogen would be directed towards the synthesis of urea necessary for osmoregulatory purposes. North Pacific spiny dogfish (Squalus acanthias suckleyi) were fed a single meal of 7 mmol l-1 15NH4Cl in a 2% ration by body mass of herring slurry via gavage. Dietary labelled nitrogen was tracked from ingestion to tissue incorporation and the subsequent synthesis of nitrogenous compounds (urea, glutamine, bulk amino acids, protein) in the intestinal spiral valve, plasma, liver and muscle. Within 20 h post-feeding, we found labelled nitrogen was incorporated into all tissues examined. The highest δ15N values were seen in the anterior region of the spiral valve at 20 h post-feeding, suggesting this region was particularly important in assimilating the dietary labelled nitrogen. In all tissues examined, enrichment of the nitrogenous compounds was sustained throughout the 168 h experimental period, highlighting the ability of these animals to retain and use dietary nitrogen for both osmoregulatory and somatic processes.

First records of the Pacific sleeper shark Somniosus cf. pacificus in the western tropical Pacific.

Technological advances have enabled the expansion of ocean exploration to include the deep ocean, providing new species observations. Here, the authors present two new observations, captured by deep-sea cameras, of the sleeper shark Somniosus cf. pacificus from the Solomon Islands and Palau. This presents the first observation of S. cf. pacificus in the western Pacific tropics and extends its range about 2000 nautical miles south. The observations presented here provide much-needed information on the range of this species which can help guide future management and conservation actions.

First recorded occurrence of the parasitic barnacle (Anelasma squalicola) on a Greenland shark (Somniosus microcephalus) in the Canadian Arctic.

A solitary Anelasma squalicola specimen was collected from the cloaca of a Greenland shark (Somniosus microcephalus), the first time this association has been recorded. The specimen's identity was confirmed through morphological and genetic assessment (mitochondrial markers: COI and control region). A. squalicola is a species typically associated with deep-sea lantern sharks (Etmopteridae) and, until the present observation, had never been observed at a sexually mature size in the absence of a mating partner. Given the reported negative effects of this parasite on its hosts, monitoring Greenland sharks for additional cases is recommended.

Untangling the systematic dilemma behind the roughskin spurdog Cirrhigaleus asper (Merrett, 1973) (Chondrichthyes: Squaliformes), with phylogeny of Squalidae and a key to Cirrhigaleus species.

Cirrhigaleus comprises a small genus of rare barbel-bearing dogfish sharks with distributions in limited regions of all oceans. Generic validity and taxonomic status of some species are upon controversies by morphological and molecular evidence that often suggest reallocation of Cirrhigaleus species into the genus Squalus. Particularly, the roughskin spurdog C. asper exhibits intermediary morphological characteristics within Squalidae that requires clarification. In the present study, a phylogenetic approach was undertaken to test the correct generic placement of C. asper using novel and revised morphological characters. We performed maximum parsimony analysis of 51 morphological characters of the internal (e.g., neurocranium, clasper cartilages, pectoral and pelvic girdles) and external anatomy applied to 13 terminal taxa. Cirrhigaleus represents a valid genus and it is supported by eight synapomorphies: high number of monospondylous vertebrae; medial nasal lobe supported by fleshy core and innervated by the buccopharyngeal branch of the facial nerve; neurocranium with greatest width across nasal capsules; one facet and one condyle in the puboischiadic bar for articulating with the basipterygium; two intermediate segments between the basipterygium of the pelvic fin and the axial cartilage of the claspers; five terminal clasper cartilages; and posterior medial process of the puboischiadic bar absent. Cirrhigaleus asper is sister-species to a small clade comprising C. barbifer and C. australis which is supported by one synapomorphy, presence of conspicuous cusplets in the dermal denticles. Cirrhigaleus barbifer, C. asper and C. australis are redescribed herein and the neotype of C. barbifer is designated. A key to Cirrhigaleus species is also given and the inner relationships within Squalus is tentatively discussed.

Localization and Characterization of Major Neurogenic Niches in the Brain of the Lesser-Spotted Dogfish Scyliorhinus canicula.

Adult neurogenesis is defined as the ability of specialized cells in the postnatal brain to produce new functional neurons and to integrate them into the already-established neuronal network. This phenomenon is common in all vertebrates and has been found to be extremely relevant for numerous processes, such as long-term memory, learning, and anxiety responses, and it has been also found to be involved in neurodegenerative and psychiatric disorders. Adult neurogenesis has been studied extensively in many vertebrate models, from fish to human, and observed also in the more basal cartilaginous fish, such as the lesser-spotted dogfish, Scyliorhinus canicula, but a detailed description of neurogenic niches in this animal is, to date, limited to the telencephalic areas. With this article, we aim to extend the characterization of the neurogenic niches of S. canicula in other main areas of the brain: we analyzed via double immunofluorescence sections of telencephalon, optic tectum, and cerebellum with markers of proliferation (PCNA) and mitosis (pH3) in conjunction with glial cell (S100ß) and stem cell (Msi1) markers, to identify the actively proliferating cells inside the neurogenic niches. We also labeled adult postmitotic neurons (NeuN) to exclude double labeling with actively proliferating cells (PCNA). Lastly, we observed the presence of the autofluorescent aging marker, lipofuscin, contained inside lysosomes in neurogenic areas.

Cerebral arterial and ventricular morphology of the dogfish (Squalus acanthias), American bullfrog (Rana catesbeiana), and green iguana (Iguana iguana): Arterial high-resolution micro-CT, dissection, and radiography study.

This study's objective was to investigate obtaining high-resolution micro-computed tomography (CT) imaging of the injected arterial circulation of the brains of the dogfish (Squalus acanthias), American bullfrog (Rana catesbeiana), and green iguana (Iguana iguana). No micro-CT images of the arterial morphology of the brains of these vertebrates were previously published. Micro-CT imaging was performed on brains that had the cerebral arterial and ventricular systems injected with a radiopaque barium-gelatin compound in the early 1970s. These specimens were dissected and placed in a preservative fluid for 35 years, until imaged with micro-CT. The obtained micro-CT images were processed with a software program that provided 3D rotational motion rendering, and sequential display of 2D renderings of the micro-CT data. The anatomic information provided by the high-resolution micro-CT is not reproducible by any other radiopaque contrast currently available, without tissue removal corrosion, and enhanced the dissection information. The digital videos of the micro-CT 3D rotational motion rendering and sequential display of 2D renderings of the dogfish, bullfrog, and green iguana, demonstrate the extent of the arterial network within the brain, the arterial segments obscured by overlying structures such as nerves, and identified in the bullfrog the venous cerebral circulation resulting from the centrifugal leptomeningeal arterial capillaries. The rotational 3D images separated superimposed arterial structures, and the sequential display of the 2D renderings clarifies the relationship of cut or overlapped arterial branches. Comparing the brain and arterial morphology of the dogfish, bullfrog, and green iguana demonstrates some of the evolutionary modifications in these vertebrates.

Stress related blood values in Scyliorhinus canicula as live-indicators of physiological status after bottom trawling capture activity.

The quantification of capture-related physiological stress is an important factor when assessing the potential for post-release survival in sharks that are incidentally captured. In the absence of these biological data and when the post-release fate is unknown, effective management plans cannot be formulated and may lead to highly susceptible shark populations being overfished. Here, we measured the levels of lactate, glucose, alanine amino transferase (ALT), aspartate amino transferase (AST), Ca2+, Na+ K+,Cl - Mg 2+ and Pi in the plasma of mature and immature lesser spotted dogfish (Scyliorhinus canicula, herein dogfish) which were incidentally captured at two depths (shallow: 50-200 m, and deep: 201-500 m) by bottom trawl off the coast of southern Sicily. These values were used as biomarkers and physiological indicators of the secondary stress response associated with capture. This study found that dogfish captured in deeper waters (below 200 m) had elevated levels of glucose, Na+, Ca2+ and K+ compared to those inhabiting depths less than <200 m. We hypothesize that the elevated levels of physiological stress in dogfish captured at greater depths may be related to the prolonged duration of the interactions with the fishing gear in the area off southern Sicily. Our findings provide new data on the capture-related stress in dogfish and increase the understanding of the potential for post-release survival in sharks captured at two depths by bottom trawl, information that is important for improving the general management plans for the fishery. However, our PC Analysis results revealed that Maturity have a positive contribution from the sample weight, sample length, ALT, AST and a negative contribution from Pi.

Escape response kinematics in two species of tropical shark: short escape latencies and high turning performance.

Accelerative manoeuvres, such as fast-starts, are crucial for fish to avoid predation. Escape responses are fast-starts that include fundamental survival traits for prey that experience high predation pressure. However, no previous study has assessed escape performance in neonate tropical sharks. We quantitatively evaluated vulnerability traits of neonate tropical sharks by testing predictions on their fast-start escape performance. We predicted (1) high manoeuvrability, given their high flexibility, but (2) low propulsive locomotion owing to the drag costs associated with pectoral fin extension during escape responses. Further, based on previous work on dogfish, Squalus suckleyi, we predicted (3) long reaction times (as latencies longer than teleosts, >20 ms). We used two-dimensional, high-speed videography analysis of mechano-acoustically stimulated neonate blacktip reef shark, Carcharhinus melanopterus (n=12), and sicklefin lemon shark, Negaprion acutidens (n=8). Both species performed a characteristic C-start double-bend response (i.e. two body bends), but single-bend responses were only observed in N. acutidens. As predicted, neonate sharks showed high manoeuvrability with high turning rates and tight turning radii (3-11% of body length) but low propulsive performance (i.e. speed, acceleration and velocity) when compared with similar-sized teleosts and S. suckleyi. Contrary to expectations, escape latencies were <20 ms in both species, suggesting that the neurophysiological system of sharks when reacting to a predatory attack may not be limited to long response times. These results provide a quantitative assessment of survival traits in neonate tropical sharks that will be crucial for future studies that consider the vulnerability of these sharks to predation.

Osmorespiratory compromise in an elasmobranch: oxygen consumption, ventilation and nitrogen metabolism during recovery from exhaustive exercise in dogfish sharks (Squalus suckleyi).

The functional trade-off between respiratory gas exchange versus osmolyte and water balance that occurs at the thin, highly vascularized gills of fishes has been termed the osmorespiratory compromise. Increases in gas exchange capacity for meeting elevated oxygen demands can end up favoring the passive movement of osmolytes and water, potentially causing a disturbance in osmotic balance. This phenomenon has been studied only sparsely in marine elasmobranchs. Our goal was to evaluate the effects of exhaustive exercise (as a modulator of oxygen demand) on oxygen consumption (MO2), branchial losses of nitrogenous products (ammonia and urea-N), diffusive water exchange rates, and gill ventilation (frequency and amplitude), in the Pacific spiny dogfish (Squalus suckleyi). To that end, MO2, osmolyte fluxes, diffusive water exchange rate, and ventilation dynamics were first measured under resting control conditions, then sharks were exercised until exhaustion (20 min), and the same parameters were monitored for the subsequent 4 h of recovery. While MO2 nearly doubled immediately after exercise and remained elevated for 2 h, ventilation dynamics did not change, suggesting that fish were increasing oxygen extraction efficiency at the gills. Diffusive water flux rates (measured over 0-2 h of recovery) were not affected. Ammonia losses were elevated by 7.6-fold immediately after exercise and remained elevated for 3 h into recovery, while urea-N losses were elevated only 1.75-fold and returned to control levels after 1 h. These results are consistent with previous investigations using different challenges (hypoxia, high temperature) and point to a tighter regulation of urea-N conservation mechanisms at the gills, likely due to the use of urea as a prized osmolyte in elasmobranchs. Environmental hyperoxia offered no relief from the osmorespiratory compromise, as there were no effects on any of the parameters measured during recovery from exhaustive exercise.

The gut microbiome may influence post-prandial nitrogen handling in an elasmobranch, the Pacific spiny dogfish (Squalus suckleyi).

Nitrogen recycling through the gut microbiome is an important mechanism used throughout vertebrates to reclaim valuable nitrogen trapped in urea. Evidence suggests it may be especially important in nitrogen limited animals, yet little is known about its role in marine elasmobranchs, which are said to be severely nitrogen limited. In the present study we used antibiotics to deplete the gut microbiome of Pacific spiny dogfish and assessed the role of the microbiome in nitrogen handling in both fed and fasted states. In fed animals, antibiotic treatment eliminated the activity of the microbial enzyme urease and reduced cellulase activity by 78%. This reduction in microbial enzyme activity resulted in significantly lower plasma urea levels which then trended upward as urea excretion rates decreased. Ammonia excretion rates were also significantly lower in antibiotic treated fish compared to the control fed. Finally, antibiotic treated fed individuals lost an average of 7.4% of their body mass while the fed controls lost only 1.8% of their body mass. Nitrogen handling in fasted animals was not significantly impacted by a reduction in microbial activity. These results suggest that compromising the gut microbiome significantly influences post-prandial nitrogen handling in spiny dogfish, and that the recycling of urea­nitrogen may be vital to maintaining nitrogen balance in these fish.

Trace and rare earth element bioaccumulation in the spotted dogfish (Scyliorhinus stellaris).

Metals (trace elements and rare earth elements, REEs) were analysed by inductively coupled plasma-mass spectrometry in blood, the liver, the kidney and muscle of ex situ spotted dogfish (Scyliorhinus stellaris). The controlled environment in which these elasmobranchs were hosted allowed to assess a baseline level of metals in the different organs since exposure via water and food can be easily monitored. The highest arsenic, chromium, copper, and iron values were found in the liver, cobalt in the kidney, and cadmium and rubidium in muscle. The highest total trace elements content was found in the trend liver (75 mg kg-1) > blood (33 mg kg-1) > muscle (31 mg kg-1) > kidney (10 mg kg-1), while the ΣREEs was the liver (30 µg kg-1) > muscle (15 µg kg-1) > kidney (13 µg kg-1) > blood (4.1 µg kg-1). Between REEs, the most represented element was scandium. Significant differences in the concentration of metals among organs were observed for almost all elements. Nonessential elements were generally lower and essential elements higher in the examined specimens compared to wild elasmobranchs, suggesting a close relationship between a balanced diet and animal welfare.

Life in the slow lane: field metabolic rate and prey consumption rate of the Greenland shark (Somniosus microcephalus) modelled using archival biologgers.

Field metabolic rate (FMR) is a holistic measure of metabolism representing the routine energy utilization of a species living within a specific ecological context, thus providing insight into its ecology, fitness and resilience to environmental stressors. For animals that cannot be easily observed in the wild, FMR can also be used in concert with dietary data to quantitatively assess their role as consumers, improving understanding of the trophic linkages that structure food webs and allowing for informed management decisions. Here, we modelled the FMR of Greenland sharks (Somniosus microcephalus) equipped with biologger packages or pop-up archival satellite tags (PSATs) in two coastal inlets of Baffin Island (Nunavut) using metabolic scaling relationships for mass, temperature and activity. We estimated that Greenland sharks had an overall mean (±s.d.) FMR of 21.67±2.30 mg O2 h-1 kg-0.84 (n=30; 1-4 day accelerometer package deployments) while residing inside these cold-water fjord systems in the late summer, and 25.48±0.47 mg O2 h-1 kg-0.84 (n=6; PSATs) over an entire year. When considering prey consumption rate, an average shark in these systems (224 kg) requires a maintenance ration of 61-193 g of fish or marine mammal prey daily. As Greenland sharks are a lethargic polar species, these low FMR estimates, and corresponding prey consumption estimates, suggest they require very little energy to sustain themselves under natural conditions. These data provide the first characterization of the energetics and consumer role of this vulnerable and understudied species in the wild, which is essential given growing pressures from climate change and expanding commercial fisheries in the Arctic.

Echinocephalus caniculus n. sp. (Nematoda: Gnathostomatidae Railliet, 1895) from the lesser spotted dogfish Scyliorhinus canicula (L.) (Elasmobranchii: Scyliorhinidae Gill, 1862) off Tunisia, with a key to species of the genus Echinocephalus.

Echinocephalus caniculus n. sp. (Nematoda, Gnathostomatidae Railliet, 1895) was isolated from the spiral valve of the lesser spotted dogfish Scyliorhinus canicula (L.) from the waters off Kalaat El Andalous, North East Tunisia. This new species is mainly characterized by a cephalic bulb armed with 31-39 transverse rows of uncinated hooks, a comparatively long oesophagus, short spicules and the presence of a gubernaculum. The new species differs from its congeners by having four cervical sacs of almost equal length, a higher oesophagus/body length ratio, the arrangement of the caudal papillae, the absence of a medioventral preanal organ and numerous scattered `pores´ limited to the lateral side of the posterior part of the body. This is the first report of a member of the genus Echinocephalus Molin, 1858 from the Tunisian coast, and a new host and locality record for the Gnathostomatidae. A key to the species of Echinocephalus is provided.

The aquaporin 8 (AQP8) membrane channel gene is present in the elasmobranch dogfish (Squalus acanthias) genome and is expressed in brain but not in gill, kidney or intestine.

The transport mechanisms for water, ammonia and urea in elasmobranch gill, kidney and gastrointestinal tract remain to be fully elucidated. Aquaporin 8 (AQP8) is a known water, ammonia and urea channel that is expressed in the kidney and respiratory and gastrointestinal tracts of mammals and teleost fish. However, at the initiation of this study in late 2019, there was no copy of an elasmobranch aquaporin 8 gene identified in the genebank even for closely related holocephalon species such as elephant fish (Callorhinchus milii) or for the elasmobranch little skate (Leucoraja erinacea). A transcriptomic study in spiny dogfish (Squalus acanthias) also failed to identify a copy. Hence this study has remedied this and identified the AQP8 cDNA sequence using degenerate PCR. Agarose electrophoresis of degenerate PCR reactions from dogfish tissues showed a strong band from brain cDNA and faint bands of a similar size in gill and liver. 5' and 3' RACE was used to complete the AQP8 cDNA sequence. Primers were then designed for further PCR reactions to determine the distribution of AQP8 mRNA expression in dogfish tissues. This showed that AQP8 is only expressed in dogfish brain and AQP8 therefore clearly can play no role in water, ammonia and urea transport in the gill, kidney or gastrointestinal tract. The role of AQP8 in dogfish brain remains to be determined.

Oxidative stress suppression in C. elegans by peptides from dogfish skin via regulation of transcription factors DAF-16 and HSF-1.

Functional peptides were obtained via enzymatic hydrolysis of smooth dogfish (Mustelus canis) skin. The enzyme-assisted process was optimized to achieve high yield of smooth dogfish skin peptides (SDSP). Fractions of SDSP (MW < 2 kDa, 2-5 kDa, 5-10 kDa and >10 kDa) showed in vitro antioxidant activities. The peptides <2 kDa (SDSP<2 kDa) significantly improved motility, reduced ROS and H2O2 levels of Caenorhabditis elegans, and increased its resistance to oxidative stress compared to the other peptide fractions. In vivo function of SDSP<2 kDa could be explained by their capacity to increase the expression of stress-response genes. The enhanced resistance to oxidative stress mediated by SDSP<2 kDa was dependent on DAF-16 and HSF-1. The amino acid residues and sequences of SDSP<2 kDa were characterized and revealed a higher content of hydrophobic versus polar amino acid contents. This study (especially the in vivo investigation) explored new potent antioxidant peptides derived from dogfish skin.

Aquaporin (AQP) channels in the spiny dogfish, Squalus acanthias II: Localization of AQP3, AQP4 and AQP15 in the kidney.

Three aquaporin water channel proteins, AQP3, AQP4 and AQP15 were localized to cells within the kidney of the spiny dogfish, Squalus acanthias, using an immunohistochemical approach. Dogfish kidney has two zones, the bundle zone (including five nephron segment bundles) and the sinus zone (with two major loops). In order to discriminate between the two loops, the cilia occurring in the first proximal/intermediate loop were labeled with two antibodies including an anti-acetylated tubulin antibody. The second late distal tubule loop (LDT) was identified, as the nephron in that region has no luminal cilia. Strong staining of the rabbit anti-dogfish AQP3, AQP4 (AQP4/2) or AQP15 polyclonal antibodies localized to LDT tubules. These antibodies were further co-stained with a mouse anti-Na+,K+-ATPase a5 monoclonal antibody, as Na+,K+-ATPase has previously been suggested to localize to the early distal tubule (EDT) and LDT and a mouse anti-NKCC T4 antibody, as NKCC2 was previously suggested to be located in the EDT and the second half of the LDT. In the LDT, strong AQP4/2 and AQP15 antibody staining localized together with the strong Na+,K+-ATPase antibody staining, whereas strong AQP3 antibody staining was largely separate but with an overlapping distribution. Very low levels of AQP4/2 antibody basal membrane staining was also detected in the first proximal /intermediate loop of the sinus zone. There was no mouse anti-NKCC T4 antibody staining apparent in the LDT. In the convoluted part of the bundle zone, the AQP4/2 and Na+,K+-ATPase but not the AQP3 or AQP15 antibodies stained tubule segments, with both AQP4/2 and Na+,K+-ATPase staining the EDT, and with low-level AQP4/2 staining of two other tubules of the bundle, which were most likely to be the proximal 1a (PIa) and intermediate II (IS II) tubules. The AQP4/2 antibody also stained the EDT in the straight bundle zone. The mouse anti-NKCC T4 antibody stained the apical region of EDT tubules in the convoluted bundle zone, suggesting that the antibody was binding to the NKCC2 cotransporter. The AQP15 antibody appeared to bind to the peritubular sheath surrounding bundles in the bundle zone. Due to the AQP4/2 antibody staining in the EDT that immediately proceeds and continues into the LDT, this suggested that the strong AQP4/2, AQP15 and Na+,K+-ATPase antibody staining was located at the beginning of the LDT and therefore the strong AQP3 was located at the end of the LDT. The staining of all three AQP antibodies was blocked by the peptide-antigen used to make each one, suggesting that all the staining is specific to each antibody.

Growth and maturity of the lesser-spotted dogfish Scyliorhinus canicula (Linnaeus, 1758) in the southern Portuguese continental coast.

Growth and reproductive parameters were estimated for Scyliorhinus canicula from the south-western Portuguese coast. The sample consisted of 148 specimens with total length ranging from 187 to 580 mm (82 males and 66 females). Maximum ages assigned to males and females were 12 and 13 years, respectively. Linf and k were estimated as 63.6 cm and 0.16 year-1 for males and 63.2 and 0.15 year-1 for females. Length and age at first maturity were estimated as 42.6 cm and 6 years for males and 44.5 cm and 7 years for females.

Energy and corticosteroid mobilization following an induced stress response in an elasmobranch fish, the North Pacific spiny dogfish (Squalus acanthias suckleyi).

The dominant corticosteroid in elasmobranchs, 1α-hydroxycorticosterone (1α-OHB), has a described role in mineral regulation but a presumptive role in energy balance. Energy demand in vertebrates following exposure to a stressor typically involves an immediate but transient release of glucocorticoids as a means of mobilizing available energy stores, usually in the form of glucose. Although a glucocorticoid role for 1α-OHB would be expected, direct glucocorticoid function of this steroid has yet to be reported in any elasmobranch. In addition, elasmobranchs also utilize the metabolite ß-hydroxybutyrate (ß-HB), which is thought to replace the role fatty acids play in most vertebrates as a predominant fuel source in extrahepatic tissues. To determine the mobilization of metabolites and corticosteroids during a stress event, North Pacific spiny dogfish, Squalus acanthias suckleyi, were cannulated and held in a darkened isolation box to recover (24-48 h) before being subjected to an acute air exposure or corticosterone injection. Dogfish were then serially blood sampled at nine timepoints over 48 h. Glucose, ß-HB, 1α-OHB, corticosterone, as well as lactate, pH, and osmolality were quantified in plasma samples. All measured variables increased in control and treatment groups within 48 h from the start of experimentation, and ß-HB and 1α-OHB remained elevated for the duration of the experiment. There was no linear correlation between glucose and 1α-OHB, but there was a weak (R2 = 0.230) although significant (p = 0.001), positive correlation between ß-HB and 1α-OHB. Interestingly, there were also significant correlations between increasing circulating glucose and corticosterone (R2 = 0.349; p < 0.001), and decreasing ß-HB and corticosterone concentrations (R2 = 0.180; p = 0.008). Our data suggest that following successive stressors of capture, surgery, and confinement, 1α-OHB was not correlated with circulating glucose, only weakly correlated with circulating ß-HB concentrations (R2 = 0.230; p = 0.001), and that corticosterone may also serve a role in energy mobilization in this species.