Spiny Dogfish Squalus Acanthias Research Articles

Feeding habits and dietary overlap in spiny dogfish Squalus acanthias (Squalidae) and narrowmouth catshark Schroederichthys bivius (Scyliorhinidae)

Spiny dogfish Squalus acanthias and narrowmouth catshark Schroederichthys bivius are the only two shark species commonly inhabiting the Falkland Islands shelf. The present study was undertaken to investigate their feeding habits and possible dietary overlap between the species. The diet of the spiny dogfish was dominated by Falkland herring Sprattus fuegensis and squid Loligo gahi, though it also preyed on a wide range of other fish and invertebrates. Catsharks showed a preference for invertebrates. The diet of both species showed marked variations with season, and ontogenic shifts were also evident. Dietary overlap was minimal in winter (15·4%) and maximal in spring (61·1%), the latter being due to both species preying upon spawning aggregations of S. fuegensis.

Active urea transport and an unusual basolateral membrane composition in the gills of a marine elasmobranch.

In elasmobranch fishes, urea occurs at high concentrations (350-600 mM) in the body fluids and tissues, where it plays an important role in osmoregulation. Retention of urea by the gill against this huge blood-to-water diffusion gradient requires specialized adaptations to the epithelial cell membranes. Experiments were performed to determine the mechanisms and structural features that facilitate urea retention by the gill of the spiny dogfish Squalus acanthias. Analysis of urea uptake by gill basolateral membrane vesicles revealed the presence of a phloretin-sensitive (half inhibition 0.09 mM), sodium-coupled, secondary active urea transporter (Michaelis constant = 10.1 mM, maximal velocity = 0.34 micromol. h(-1). mg protein(-1)). We propose that this system actively transports urea out of the gill epithelial cells back into the blood against the urea concentration gradient. Lipid analyses of the basolateral membrane revealed high levels of cholesterol contributing to the highest reported cholesterol-to-phospholipid molar ratio (3.68). This unique combination of active urea transport and modification of the phospholipid bilayer membrane is responsible for decreasing the gill permeability to urea and facilitating urea retention by the gill of Squalus acanthias.

The role of the pectoral fins in body trim of sharks

In a large aquarium the leopard shark Triakis semifasciata, sand tiger shark Odontaspis taurus, sandbar shark Carcharhinus plumbeus, and spiny dogfish Squalus acanthias cruised steadily at 0·1‐0·7 body lengths s‐1. Relative to the trajectory of the shark, the pectoral fins were maintained at a positive angle of ttack regardless of vertical direction. For level swimming the mean angle of attack for the pectoral fin was 11±1·7, 10·1±1·3°, 9·3±1·3°, and 15·0±0·0 for T. semifasciata, C. plumbeus, O. taurus, and S. acanthias, respectively. The long axis of the body was canted at an angle of attack for T. semifasciata and S. acanthias, but trim was maintained during level swimming for C. plumbeus and O. taurus. Hydrodynamic analysis of the body and fin design of T. semifasciata indicated that the pectoral fins could develop suffcient pitching moment to maintain depth and keep the body in trim. Demonstration of positive angles of attack support the hypothesis that lift is generated in the anterior body to counterbalance the lift produced by the heterocercal tail.

Development of an acoustic telemetry tag for monitoring electromyograms in free-swimming fish

We report the development of an acoustic telemetry tag used to monitor electromyograms (EMGs) remotely from free-swimming marine fish. The device described amplifies and filters the EMG and then converts the electrical waveform into a frequency-modulated acoustic signal that is transmitted through water. The signal is then received, demodulated and recorded by the receiving system. The EMG tag described has been tested on a range of species, including toadfish Opsanus &tgr;, spiny dogfish Squalus acanthias, yellowfin tuna Thunnus albacares and eastern Pacific bonito Sarda chiliensis, in different tank environments. In certain tanks the fidelity with which the system replicates the EMG is sufficient to quantify accurately the onset, offset, duration, the integrated area under the absolute value of the signal and the number of signal zero crossings. This EMG tag will expand the scope of questions that can be addressed about the behavior and physiology of free-swimming fish.

Molecular and functional characterization of s-KCNQ1 potassium channel from rectal gland of Squalus acanthias.

Functional and pharmacological data point to the involvement of KCNQ1/IsK potassium channels in the basolateral potassium conductance of secretory epithelia. In this study, we report the cloning and electrophysiological characterization of the KCNQ1 protein from the salt secretory rectal gland of the spiny dogfish (Squalus acanthias). The S. acanthias KCNQ1 (s-KCNQ1) cDNA was cloned by polymerase chain reaction (PCR) intensive techniques and showed overall sequence similarities with the KCNQ1 potassium channel subunits of Man, mouse and Xenopus laevis of 64, 70 and 77%, respectively, at the translated amino acid level. Analysis of s-KCNQ1 expression on a Northern blot containing RNA from heart, rectal gland, kidney, brain, intestine, testis, liver and gills revealed distinct expression of 7.4-kb s-KCNQ1 transcripts only in rectal gland and heart. Voltage-clamp analysis of s-KCNQ1 expressed in Xenopus oocytes showed pronounced electrophysiological similarities to human and murine KCNQ1 isoforms, with a comparable sensitivity to inhibition by the chromanol 293B. Coexpression of s-KCNQ1 with human-IsK (h-IsK) induced currents with faster activation kinetics and stronger rectification than observed after coexpression of human KCNQ1 with h-IsK, with the voltage threshold of activation shifted to more negative potentials. The low activation threshold at approximately -60 mV in combination with the high expression in rectal gland cells make s-KCNQ1 a potential candidate responsible for the basolateral potassium conductance.

Conservation and variation in the feeding mechanism of the spiny dogfish squalus acanthias

Changes in the feeding mechanism with feeding behavior were investigated using high-speed video and electromyography to examine the kinematics and motor pattern of prey capture, manipulation and transport in the spiny dogfish Squalus acanthias (Squalidae: Squaliformes). In this study, Squalus acanthias used both suction and ram behaviors to capture and manipulate prey, while only suction was used to transport prey. The basic kinematic feeding sequence observed in other aquatic-feeding lower vertebrates is conserved in the spiny dogfish. Prey capture, bite manipulation and suction transport events are characterized by a common pattern of head movements and motor activity, but are distinguishable by differences in duration and relative timing. In general, capture events are longer in duration than manipulation and transport events, as found in other aquatic-feeding lower vertebrates. Numerous individual effects were found, indicating that individual sharks are capable of varying head movements and motor activity among successful feeding events. Upper jaw protrusion in the spiny dogfish is not restricted by its orbitostylic jaw suspension; rather, the upper jaw is protruded by 30 % of its head length, considerably more than in the lemon shark Negaprion brevirostris (Carcharhinidae: Carcharhiniformes) (18 %) with its hyostylic jaw suspension. One function of upper jaw protrusion is to assist in jaw closure by protruding the upper jaw as well as elevating the lower jaw to close the gape, thus decreasing the time to jaw closure. The mechanism of upper jaw protrusion was found to differ between squaliform and carcharhiniform sharks. Whereas the levator palatoquadrati muscle assists in retracting the upper jaw in the spiny dogfish, it assists in protruding the upper jaw in the lemon shark. This study represents the first comprehensive electromyographic and kinematic analysis of the feeding mechanism in a squaliform shark.

Accumulation of 210Po by spiny dogfish (Squalus acanthias), elephant fish (Callorhinchus milii) and red gurnard (Chelodonichthys kumu) in New Zealand shelf waters

Concentrations of the natural radionuclide 210Po in the livers of 81 individual specimens of three fish species collected from waters of the Otago continental shelf, New Zealand, have been measured: spiny dogfish (Squalus acanthias), 4·2 ± 1·8 Bq kg-1 wet weight (mean ± standard deviation, n = 48); elephant fish (Callorhinchus milii), 136 ± 39 Bq kg-1 (n = 7); and red gurnard (Chelodonichthys kumu), 38 ± 13 Bq kg-1 (n = 26). Separate measurements showed that only a negligible fraction of the 210Po was supported by decay of the 210Pb parent (210Po/210Pb activity ratios were 15, 134 and 5·9 respectively for the three species), indicating that direct uptake of 210Po into the liver balances losses from excretion and radioactive decay. The radiation dose from 210Po in the livers accounted for between 88% and 99% of the total internal absorbed dose received by the fish species. The activity of 210Po in sea water from the study area was 0·9–2·2 mBq L-1, yielding concentration factors for 210Po in liver tissue in the range 3 × 103 to 100 × 103. No significant monophasic relationships were observed between the 210Po results and the measured concentrations of the elements Cd, Cu, Fe, Mn, Zn and Pb, except that Pb and 210Po were correlated (r = 0·511) in C. kumu.

Extracellular carbonic anhydrase and an acid-base disequilibrium in the blood of the dogfish Squalus acanthias

The electrometric [Delta]pH method and an in vitro radioisotopic HCO3- dehydration assay were used to demonstrate the presence of true extracellular carbonic anhydrase (CA) activity in the blood of the Pacific spiny dogfish Squalus acanthias. An extracorporeal circulation and stopflow technique were then used to characterise the acid­base disequilibrium in the arterial (postbranchial) blood. During the stopflow period, arterial pH (pHa) decreased by 0.028±0.003 units (mean ± s.e.m., N=27), in contrast to the increase in pHa of 0.029±0.006 units (mean ± s.e.m., N=6) observed in seawater-acclimated rainbow trout Oncorhynchus mykiss under similar conditions. The negative disequilibrium in dogfish blood was abolished by the addition of bovine CA to the circulation, while inhibition by benzolamide of extracellular and gill membrane-bound CA activities reversed the direction of the acid­base disequilibrium such that pHa increased by 0.059±0.016 units (mean ± s.e.m., N=6) during the stopflow period. When the CA activity of red blood cells (rbcs) was additionally inhibited using acetazolamide, the magnitude of the negative disequilibrium was increased significantly to -0.045±0.007 units (mean ± s.e.m., N=6). Blockage of the rbc Cl-/HCO3- exchanger using 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) also increased the magnitude of the negative disequilibrium, in this case to -0.089±0.008 units (mean ± s.e.m., N=6). Exposure of dogfish to hypercapnia had no effect on the disequilibrium, whereas the disequilibrium was significantly larger under hypoxic conditions, at -0.049±0.008 units (mean ± s.e.m., N=6). The results are interpreted within a framework in which the absence of a positive CO2 excretion disequilibrium in the arterial blood of the spiny dogfish is attributed to the membrane-bound and extracellular CA activities. The negative disequilibrium may arise from the continuation of Cl-/HCO3- exchange in the postbranchial blood and/or the hydration of CO2 added to the plasma postbranchially. Two possible sources of this CO2 are discussed; rbc CO2 production or the admixture of blood having 'low' and 'high' CO2 tensions, i.e. the mixing of postbranchial blood with blood which has bypassed the respiratory exchange surface.

Vasoactivity and immunoreactivity of fish tachykinins in the vascular system of the spiny dogfish.

Tachykinin control of gut blood flow (measured by pulsed Doppler technique), dorsal aortic pressure, and heart rate were studied in unrestrained spiny dogfish Squalus acanthias injected with the elasmobranch tachykinins scyliorhinin I and II (SCY I and SCY II), the trout tachykinins substance P (SP), and neurokinin A (NKA). Effects on somatic vasculature were measured by in vitro perfusion of the isolated tail. SCY I and trout SP produced hypotension due to a general vasodilation. This caused a transient increase in mesenteric blood flow and a prolonged increase in celiac blood flow. SCY II caused an initial hypertension induced by a general vasoconstriction, followed eventually by an elevated flow in both gut arteries due to dilation of the vascular beds. Trout NKA evoked a short-lasting increase in celiac blood flow due to a decrease in vascular resistance, a late decrease in mesenteric flow due to vasoconstriction, and no effect on the somatic vasculature. None of the peptides affected heart rate. The study demonstrates a significant vasoactive function of fish tachykinins in the vascular system of an elasmobranch species and, in addition, the occurrence of tachykinin receptor subtypes. Immunohistochemistry revealed a NKA/SCY II-like peptide in nerve fibers innervating many vessels, including the celiac and the mesenteric arteries, the gastrointestinal canal, and the heart.

Myometrium of the spiny dogfish Squalus acanthias: peptide and steroid regulation

The phylogenetic age of endocrine control of viviparous reproduction in vertebrates may be estimated by examination of elasmobranch models. We have shown in pregnant Squalus acanthias that Squalus relaxin (sRLX) significantly decreased the frequency of myometrial contractions in a dose-dependent reversible manner in vitro and in vivo, without altering the intensity or duration of contractions. In contrast, neurointermediate lobe extract provoked a marked and reversible enhancement of the duration and intensity of contractions but was ineffective in altering the frequency of contractions. In steroid-primed animals, untreated and estradiol-17 beta (E2)-treated animals exhibited a decrease in the frequency of activity after injection of sRLX in vivo while pretreatment with progesterone (P4) alone or in combination with E2 fully suppressed the effects of sRLX. These results suggest that homologous sRLX slows the frequency of spontaneous uterine contractions in third-trimester sharks (stage C) in which endogenous P4 is reduced and E2 levels are rising. These data demonstrate the physiological importance of these hormones and the antiquity of reproductive tract control mechanisms.

Coexistence of NADPH-diaphorase and vasoactive intestinal polypeptide in the enteric nervous system of the Atlantic cod (Gadus morhua) and the spiny dogfish (Squalus acanthias)

The distribution of NADPH (nicotinamide adenine dinucleotide phosphate)-diaphorase in nerve cells in the gastrointestinal tract has been investigated and compared in three fish species representing different evolutionary branches. In mammals, NADPH-diphorase is identical to nitric oxide synthase (NOS) and can, in the presence of NADPH, reduce the dye nitroblue tetrazolium, resulting in a blue product. Using this method, we have found numerous NADPH-diaphorase-containing nerve cells in the myenteric plexus of the Atlantic cod (Gadus morhua) and the spiny dogfish (Squalus acanthias) but none in the hagfish (Myxine glutinosa). In the cod, nerve fibres were sparsely stained, whereas in the dogfish, they formed a dense pattern of fibre bundles. Double-staining for NADPH-diaphorase and the neuropolypeptides VIP (vasoactive intestinal polypeptide) and PACAP (pituitary adenylate cyclase activating peptide) revealed three separate populations designated VIP/NADPH, VIP/- and NADPH/-. The majority but not all of the NADPH-diaphorase-positive cells also showed VIP or PACAP immunoreactivity and vice versa. The presence of NADPH-diaphorase in neurons and the distribution of these neurons in the gastrointestinal tract of the two species indicate a physiological role for nitric oxide in the control of gut motility.

Phlyctainophora lamnae (Nematoda; Philometridae) from dogfish Squalus acanthias off southern New Zealand

Colled globose female nematodes and larvae, identified as Phlyctainophora lamnae Steiner, 1921, were found in tumour-like lesions on the tail fin of spiny dogfish Squalus acanthias L. (Squalidae) caught off southern New Zealand. Nematodes provoke a chronic inflammatory response by the host. No male nematedes were recovered. This is the first record of the genus from New Zealand and the first record of adult Phlyctainophora from the Southern Hemisphere. Phlyctainophora squali Mudrey & Dailey, 1969 is considered a synonym of P. lamnae.

Stage-related changes in steroid-converting enzyme activities in Squalus testis: synthesis of biologically active metabolites via 3β-hydroxysteroid dehydrogenase/ isomerase and 5α-reductase

To investigate the relationship between steroidogenesis and spermatogenesis, two key enzymes of androgen biosynthesis, 3β-hydroxysteroid dehydrogenase/isomerase (3β-HSD) and 5α-reductase, were compared at premeiotic (PrM), meiotic (M) and postmeiotic (PoM) stages. Staged tissues were obtained by dissection from the testis of the spiny dogfish Squalus acanthias, in which spermatogenesis is a simple diametric progression. Microsomal 3β-HSD activity was measured by conversion of [ 3H] dehydroepiandrosterone (DHEA) to androstenedione (AE). Reaction constants were: K m = 3.2 μM and V max = 243 pmol/min/mg protein. 3β-HSD increased progressively with maturation, resulting in three- to four-fold higher levels in PoM than in PrM stages. Absolute values and stage-related differences were the same, whether microsomes were derived from whole testis or from isolated spermatocysts (germ cell/Sertoli cell units), thus supporting microscopic studies showing that Sertoli cells are the primary steroidogenic elements of dogfish testis. In vitro conversion of [ 3H]testosterone to [ 3H]dihydrotesterone (DHT) was used to estimated 5α-reductase activity. Apparent substrate affinity was similar to that of 3β-HSD ( K m = 2.9 μM), but maximal product yields were two to three orders of magnitude lower ( V max = 208 fmol/min/mg protein). Also, the stage-related pattern of 5α-reductase activity ( PrM > PoM >> M) differed from that of 3β-HSD ( PoM >> M > PrM). Together with previously measured steroidogenic enzyme activities using the shark testis model, these results predict that de novo androgen biosynthesis is highest in testicular regions with mature spermatids and fully differentiated Sertoli cells, and also suggest that availability of T versus DHT for androgen receptor binding may be developmentally regulated during spermatogenesis.

Spiny Dogfish Predation on Chinook and Coho Salmon and the Potential Effects on Hatchery-Produced Salmon

-Large numbers of spiny dogfish Squalus acanthias moved into the area near the mouth of the Big Qualicum River, British Columbia, at the time hatchery-reared smolts of Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch were leaving the river in 1988 and 1989. A small percentage of the spiny dogfish preyed on the smolts, but the resulting smolt mortality is believed to have been large because of the large numbers of spiny dogfish in this area. Spiny dogfish also fed on adult salmon in the fall. The long-term decline in survival of chinook salmon produced at the Big Qualicum Hatchery was similar to the pattern of survival of other hatchery-produced salmon. We propose that this long-term decline in survival results from predation.

Molecular phylogeny of the prickly shark, Echinorhinus cookei, based on a nuclear (18S rRNA) and a mitochondrial (cytochrome b) gene

The classification of the sharks is unclear. This is particularly true for the superorder Squalomorphii. The relationships between the squalomorphs and other superorders of sharks and the relationships between the different orders within the squalomorphs are a matter of debate. Here, we report a molecular phylogeny for a little known member of this superorder, the genus Echinorhinus. Echinorhinus is most commonly classified in either the family Echinorhinidae (Squaliformes) or the family Squalidae (Squaliformes). However, some authors have suggested a closer relationship to the order Hexanchiformes. In an attempt to shed light on this controversy, we have cloned, sequenced, and compared two genes widely used in molecular phylogeny studies, the cytochrome b and the 1SS rRNA from the rare prickly shark, Echinorhinus cookei, and two potential relatives, the spiny dogfish Squalus acanthias (Squaliformes), and the sevengill shark, Notorynchus cepedianus (Hexanchiformes). The sequences of these genes for the prickly shark, the dogfish, and the sevengill shark were found to be equally divergent, suggesting that the prickly shark is no closer to the order Squaliformes than to the order Hexanchiformes.

Androgen and progesterone receptors in shark (Squalus) testis: characteristics and stage-related distribution.

Although testosterone (T) is essential for the normal completion of spermatogenesis, the exact T-sensitive control points are still unknown. Using staged tissues (premeiotic, PrM; meiotic, M; and postmeiotic, PoM) from zonal testes of the spiny dogfish Squalus acanthias, and standard [3H] steroid binding analysis, we characterized a T-binding component with physiochemical characteristics resembling classical androgen receptors (AR). [3H]T binding was of high affinity (dissociation constant = 4.4 x 10(-9) M), limited capacity (maximum binding, 94 fmol/g tissue) and relatively stable (t1/2 = 4 h at 4 C). The T-binding component was present in both cytosolic and nuclear extracts, adhered to DNA-cellulose, and displayed predicted sedimentation properties of an activated receptor in vivo or in vitro (5.06S). T, 5 alpha-dihydrotestosterone (DHT), and mibolerone (Mib), but not methyltrienelone (R1881), competed well for [3H]T binding; however, progesterone (P) was equivalent to T in its ability to displace tracer. Subsequent analysis of [3H] P binding revealed a P-binding component that was present in nuclear and cytosolic extracts, adhered to DNA, but differed from AR in its inability to bind Mib. Competition studies in which excess radioinert Mib was used to block AR revealed ligand specificity characteristics of progesterone receptors (PR): promegestone (R5020) greater than P greater than deoxycorticosterone, but T, DHT, dexamethasone, and corticosterone were ineffective competitors. Also, a nonlinear Scatchard plot was obtained, suggesting two P-binding activities, which differed in their binding affinities (dissociation constant = 0.88 vs. 5.9 x 10(-9) M) and capacities (66 vs. 210 fmol/g tissue). Conversely, using [3H]Mib to avoid interference from PR, we confirmed that T, DHT, and P were equivalent in their ability to displace ligand from AR. Comparison of tissues by stage of spermatogenesis revealed different distribution patterns for AR (PrM greater than M much greater than PoM) vs. PR (PoM much greater than M = PrM). These data provide definitive evidence for separate testicular T- and P-binding mechanisms and indicate the presence of temporally distinct sets of steroid-regulated genes.

A New Eye Disease in Pen-Reared Chinook Salmon Caused by Metacestodes ofGilquinia squali(Trypanorhyncha)

Abstract Eye infections by metacestodes of Gilquinia squali (Cestoda: Trypanorhyncha) were associated with mortality in chinook salmon Oncorhynchus tshawytscha reared in net-pens in seawater at two separate locations in British Columbia. Mortality associated with the disease was about 10% at one site and undetermined at the second site. The metacestode was found in the vitreous humor of moribund fish with eye lesions, whereas healthy fish from the same pen exhibited neither eye lesions nor the infection. The lesions were characterized by retinal folding and apparent retinal duplication, and cataractous changes; in severe cases, the cornea ruptured, and the lens was extruded. The spiny dogfish Squalus acanthias i s the definitive host for the cestode. Spiny dogfish were prevalent in and around the affected net-pen sites, thus providing coracidia to infect the first intermediate host, which is most likely a crustacean. Although the metacestode is common in the eyes of European whiting Merlangius merlangus i...

The presence of a juxtaglomerular apparatus in elasmobranch fish

Previous studies have concluded that a juxtaglomerular apparatus evolved in phylogenetic groups "higher" than elasmobranch fishes. The present study shows for the first time a distinct juxtaglomerular apparatus in four marine elasmobranchs, the spiny dogfish Squalus acanthias), the smooth dogfish (Mustelus canis), the little skate (Raja erinacea), and the cownose ray (Rhinoptera bonasus). Serial semithin sections of these fishes' kidneys reveal the four morphological components of a juxtaglomerular apparatus at the vascular pole of the renal corpuscle: (1) an afferent arteriole surrounded by smooth muscle cells which have granules containing a material exhibiting a periodic substructure comparable to that of renin granules in higher vertebrates; (2) an efferent arteriole usually devoid of smooth muscle cells but having pericyte-like cells; (3) a macula densa portion of the distal tubule juxtaposed between the afferent and efferent arterioles; and (4) elongated, fusiform cells (Goormaghtigh cells), which are in continuity with similar cells of the abundant intra-glomerular mesangium, and fill the space bordered by the distal tubule and by the afferent and efferent vessels. The distal tubule, from the site where it lies close to the afferent arteriole, moves directly toward the urinary pole, frequently indenting the renal corpuscle. Within this indentation, the tubule may be flanked by the efferent vessel, by the extraglomerular mesangium, or by Bowman's capsule only. Facing these structures the tubular epithelial cells possess basally dilated intercellular spaces. Endothelial cells of the efferent vessel(s) are fenestrated, possessing pores which are closed by a diaphragm. marine elasmobranch fish possess the morphological components of a juxtaglomerular apparatus which suggests that these fishes, like most other vertebrates, possess a renin-angiotensin system and a glomerular-tubular feedback mechanism.

Renal effects of atrial natriuretic peptide in a marine elasmobranch

The effects of atrial natriuretic peptide on the renal function of the spiny dogfish (Squalus acanthias) in seawater were evaluated. A synthetic mammalian peptide, atriopeptin II (2 micrograms/kg), was injected intravascularly into unanesthetized, unrestrained fish prepared for renal clearance studies. The aortic pressure, glomerular filtration rate (GFR), urine flow rate (V), and urinary excretion of sodium, potassium, and total osmolytes were continuously monitored. Atriopeptin II significantly decreased mean aortic pressure (-12%), GFR (-40%), V (-66%), and the absolute excretion rates of sodium (-47%), potassium (-43%), and total osmolytes (-44%). However, the renal effects of atriopeptin II were temporally dissociated from the vasodepressor effect. Mean aortic pressure decreased quickly and returned to control values approximately 2 h after injection, whereas GFR did not decrease significantly until the third hour after injection. The decreases in renal water and solute excretion in response to atriopeptin could be accounted for by the decrease in GFR, since there were no significant changes in fractional water or solute excretion. Similar decreases in GFR were observed during constant infusions of a lower physiological dose of the peptide (80 pg.kg-1.min-1). The observed antidiuretic and antinatriuretic effect of synthetic atriopeptin in the dogfish contrasts with its putative role as a hormone mediating hypervolemic regulation.

Neuropeptide Y-like immunoreactivity in the cardiovascular nerve plexus of the elasmobranchs Raja erinacea and Raja radiata

The distribution of nerves showing neuropeptide Y (NPY)-like immunoreactivity in the cardiovascular system of elasmobranchs and teleosts has been investigated. Two species of teleosts, the rainbow trout (Salmo gairdneri) and the Atlantic cod (Gadus morhua), and three species of elasmobranchs, the spiny dogfish (Squalus acanthias), the little skate (Raja erinacea) and the starry ray (Raja radiata), were used in this study. An innervation of the cardiovascular system by an NPY-like substance was found only in the two species of Raja. A rich innervation was encountered in these skates, with the highest density of fibres in the wall of the ventricle, the conus arteriosus, the coeliac artery and smaller mesenterial vessels. In the vessels, the fibres formed a plexus at the adventitio-mediol border. Few fibres were found in the walls of the dorsal aorta, the sinus venosus and the atrium, and no fibres were observed in the walls of the ventral aorta. Falck-Hillarp fluorescence histochemistry showed the presence of a rich innervation of arteries and arterioles of the gut by catecholamine-containing nerve fibres.