Squalid Research Articles

Time course of the acute response of the North Pacific spiny dogfish shark (Squalus suckleyi) to low salinity

Dogfish are considered stenohaline sharks but are known to briefly enter estuaries. The acute response of North Pacific spiny dogfish (Squalus suckleyi) to lowered salinity was tested by exposing sharks to 21‰ salinity for 48h. Temporal trends in blood pH, plasma osmolality, CO2, HCO3−, Na+, Cl−, K+, and urea concentrations, and in the rates of urea efflux and O2 consumption, were quantified. The rate of O2 consumption exhibited cyclic variation and was significantly depressed by lowered salinity. After 9h, plasma [Cl−] stabilized at 9% below initial levels, while plasma [Na+] decreased by more than 20% within the first 12h. Plasma [urea] dropped by 15% between 4 and 6h, and continued to decrease. The rate of urea efflux increased over time, peaking after 36h at 72% above the initial rate. Free-swimming sharks subjected to the same salinity challenge survived over 96h and differed from cannulated sharks with respect to patterns of Na+ and urea homeostasis. This high-resolution study reveals that dogfish exposed to 21‰ salinity can maintain homeostasis of Cl− and pH, but Na+ and urea continue to be lost, likely accounting for the inability of the dogfish to fully acclimate to reduced salinity.

Non-Genotoxic Assessment of a Natural Antimicrobial Agent: Squalamine

Squalamine, a natural aminosterol compound isolated from the dogfish shark Squalus acanthias, is reported to possess high antimicrobial activities. Herein, we assessed its in vitro genotoxic properties by using the Ames test and the micronucleus assay. All the experimental results demonstrate that squalamine is a non genotoxic molecule and call for further work to evaluate its potent human therapeutic use as a new class of antinfectious agents. Keywords: Ames test, antimicrobial agent, non-genotoxic, squalamine.

Isolation and characterization of gelatin from the skins of skipjack tuna (Katsuwonus pelamis), dog shark (Scoliodon sorrakowah), and rohu (Labeo rohita)

Gelatin was extracted from the skins of dog shark (Scoliodon sorrakowah), skipjack tuna (Katsuwonus pelamis) and rohu (Labeo rohita) and their physico-chemical properties were measured. The skins of shark, tuna and rohu yielded 19.7, 17.2 and 11.3% gelatin, respectively. The gel strength of dog shark gelatin (6.67%, 10°C) was found to be higher (206 g) than tuna and rohu skin gelatins (177g and 124g, respectively). Similarly, molecular weight, viscosity, melting point, foaming properties, water holding capacity, odour, colour and clarity of dog shark gelatin were in general better than the tuna and rohu skin gelatins. The amino acid analysis showed that hydroxyproline content in dog shark skin gelatin was the highest when compared to tuna and rohu skin gelatins.

CGMP inhibition of type 3 phosphodiesterase is the major mechanism by which C-type natriuretic peptide activates CFTR in the shark rectal gland

The in vitro perfused rectal gland of the dogfish shark (Squalus acanthias) and filter-grown monolayers of primary cultures of shark rectal gland (SRG) epithelial cells were used to analyze the signal transduction pathway by which C-type natriuretic peptide (CNP) stimulates chloride secretion. CNP binds to natriuretic receptors in the basolateral membrane, elevates cellular cGMP, and opens cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels in the apical membrane. CNP-provoked chloride secretion was completely inhibitable by the nonspecific protein kinase inhibitor staurosporine and the PKA inhibitor H89 but insensitive to H8, an inhibitor of type I and II isoforms of cGMP-dependent protein kinase (cGKI and cGKII). CNP-induced secretion could not be mimicked by nonhydrolyzable cGMP analogs added alone or in combination with the protein kinase C activator phorbolester, arguing against a role for cGK or for cGMP-induced PKC signaling. We failed to detect a dogfish ortholog of cGKII by molecular cloning and affinity chromatography. However, inhibitors of the cGMP-inhibitable isoform of phosphodiesterase (PDE3) including milrinone, amrinone, and cilostamide but not inhibitors of other PDE isoenzymes mimicked the effect of CNP on chloride secretion in perfused glands and monolayers. CNP raised cGMP and cAMP levels in the SRG epithelial cells. This rise in cAMP as well as the CNP and amrinone-provoked chloride secretion, but not the rise in cGMP, was almost completely blocked by the Gαi-coupled adenylyl cyclase inhibitor somatostatin, arguing against a role for cGMP cross-activation of PKA in CNP action. These data provide molecular, functional, and pharmacological evidence for a CNP/cGMP/PDE3/cAMP/PKA signaling cascade coupled to CFTR in the SRG.

Transcriptome responses in the rectal gland of fed and fasted spiny dogfish shark (Squalus acanthias) determined by suppression subtractive hybridization

Prior studies of the elasmobranch rectal gland have demonstrated that feeding induces profound and rapid up regulation of the gland's ability to secrete concentrated NaCl solutions and the metabolic capacity to support this highly ATP consuming process. We undertook the current study to attempt to determine the degree to which up regulation of mRNA transcription was involved in the gland's activation. cDNA libraries were created from mRNA isolated from rectal glands of fasted (7days post-feeding) and fed (6h and 22h post-feeding) spiny dogfish sharks (Squalus acanthias), and the libraries were subjected to suppression subtractive hybridization (SSH) analysis. Quantitative real time PCR (qPCR) was also used to ascertain the mRNA expression of several genes revealed by the SSH analysis. In total the treatments changed the abundance of 170 transcripts, with 103 up regulated by feeding, and 67 up regulated by fasting. While many of the changes took place in ‘expected’ Gene Ontology (GO) categories (e.g., metabolism, transport, structural proteins, DNA and RNA turnover, etc.), KEGG analysis revealed a number of categories which identify oxidative stress as a topic of interest for the gland. GO analysis also revealed that branched chain essential amino acids (e.g., valine, leucine, isoleucine) are potential metabolic fuels for the rectal gland. In addition, up regulation of transcripts for many genes in the anticipated GO categories did not agree (i.e., fasting down regulated in feeding treatments) with previously observed increases in their respective proteins/enzyme activities. These results suggest an ‘anticipatory’ storage of selected mRNAs which presumably supports the rapid translation of proteins upon feeding activation of the gland.

Evaluating the Efficiency of Flushed Stomach-tube Lavage for Collecting Stomach Contents from Dogfish Sharks

Concern over the use of lethal techniques to collect basic biological data from sharks has necessitated the development of nonlethal methods of data collection. We evaluated the nonlethal method of removing stomach contents using acrylic tubes. Stomach contents of Spiny Dogfish (Squalus acanthias) captured with bottom trawls and longlines were collected using acrylic tubes flushed with seawater. The largest tube used during the trawl survey was 30 mm in diameter, while a larger tube (37 mm in diameter) was used during longline sampling due to catches of larger dogfish. The average ef- ficiency of stomach content removal was 79.5% overall, and improved to 93% with the addition of the larger tube. Selection of a tube with a diameter 10-20 mm less than mouth width can be reasonably expected to recover over 90% of stomach contents. Stomach- tube lavage is a useful and efficient method for nonlethal sampling of stomach contents from Spiny Dogfish, and perhaps other small sharks.

Anatomy and muscle activity of the dorsal fins in bamboo sharks and spiny dogfish during turning maneuvers

Stability and procured instability characterize two opposing types of swimming, steady and maneuvering, respectively. Fins can be used to manipulate flow to adjust stability during swimming maneuvers either actively using muscle control or passively by structural control. The function of the dorsal fins during turning maneuvering in two shark species with different swimming modes is investigated here using musculoskeletal anatomy and muscle function. White-spotted bamboo sharks are a benthic species that inhabits complex reef habitats and thus have high requirements for maneuverability. Spiny dogfish occupy a variety of coastal and continental shelf habitats and spend relatively more time cruising in open water. These species differ in dorsal fin morphology and fin position along the body. Bamboo sharks have a larger second dorsal fin area and proportionally more muscle insertion into both dorsal fins. The basal and radial pterygiophores are plate-like structures in spiny dogfish and are nearly indistinguishable from one another. In contrast, bamboo sharks lack basal pterygiophores, while the radial pterygiophores form two rows of elongated rectangular elements that articulate with one another. The dorsal fin muscles are composed of a large muscle mass that extends over the ceratotrichia overlying the radials in spiny dogfish. However, in bamboo sharks, the muscle mass is divided into multiple distinct muscles that insert onto the ceratotrichia. During turning maneuvers, the dorsal fin muscles are active in both species with no differences in onset between fin sides. Spiny dogfish have longer burst durations on the outer fin side, which is consistent with opposing resistance to the medium. In bamboo sharks, bilateral activation of the dorsal in muscles could also be stiffening the fin throughout the turn. Thus, dogfish sharks passively stiffen the dorsal fin structurally and functionally, while bamboo sharks have more flexible dorsal fins, which result from a steady swimming trade off.

RE-DESCRIPTION OF THE EXTERNAL MORPHOLOGY OF SOMNIOSUS ROSTRATUS (RISSO, 1826), WITH SPECIAL REFERENCE TO ITS SQUAMATION AND CUTANEOUS SENSORY ORGANS, AND ASPECTS OF THEIR FUNCTIONAL MORPHOLOGY (PISCES SELACHII SQUALIDAE)

SUMMARY The availability of a new S. rostratus (Risso, 1826) specimen (Pisces Selachii Squalidae), the re-examination of two museum collections and a survey of literature on the subject has provided the opportunity to clarify some problems concerning this shark and other species of the genus Somniosus. The main topics investigated were morphometric characters, squamation morphogenesis, distribution of cutaneous sensory organs and modified scales. Morpho-functional problems are discussed, with special reference to hydrodynamic aspects. The little sleeper, S. rostratus, has a typical squaloid morphology. In all ontogenetic stages, a peculiar short keel occurs in the caudal peduncle, above the ventral hypochordal lobe. The function of the keel could be to improve turning ability and/or to act as a stabilizer. The caudal morphology belongs to the squaloid type (THOMSON & SIMANEK, 1977) and differs from that of the strictly benthic species. On this basis we therefore believe that S. rostratus is a benthopelagi...

Residues, sources and tissue distributions of organochlorine pesticides in dog sharks (Mustelus griseus) from Zhoushan Fishing Ground, China

Ten dog sharks (Mustelus griseus) collected from Zhoushan Fishing Ground, China, were analysed for organochlorine pesticides in various tissues, including muscle, liver, skin, gill and fin, with the aim to study the residues, sources and tissue distributions of these chemicals in high trophic level marine fishes. The concentrations of DDTs, HCHs, and chlordanes varied from 7.27–26.62, 2.67–3.35, and 0.54–0.61ng/g wet weight, respectively, with the estimated daily intake far below the acceptable daily intake and Chinese edible hygienic criteria. Data from the tissue distribution suggested a tendency of DDTs and chlordanes to accumulate in the liver, but for HCHs, direct gill penetration may be an important means of entrance. In addition, the compositional profiles indicated that the residues of HCHs and chlordanes mainly originated from the historical usage of these chemicals. However, the predominant maternal compounds and the o,p′-DDT/p,p′-DDT ratios reflected a recent use of dicofol.

Atypical Antigen Recognition Mode of a Shark Immunoglobulin New Antigen Receptor (IgNAR) Variable Domain Characterized by Humanization and Structural Analysis

The immunoglobulin new antigen receptors (IgNARs) are a class of Ig-like molecules of the shark immune system that exist as heavy chain-only homodimers and bind antigens by their single domain variable regions (V-NARs). Following shark immunization and/or in vitro selection, V-NARs can be generated as soluble, stable, and specific high affinity monomeric binding proteins of ∼12 kDa. We have previously isolated a V-NAR from an immunized spiny dogfish shark, named E06, that binds specifically and with high affinity to human, mouse, and rat serum albumins. Humanization of E06 was carried out by converting over 60% of non-complementarity-determining region residues to those of a human germ line Vκ1 sequence, DPK9. The resulting huE06 molecules have largely retained the specificity and affinity of antigen binding of the parental V-NAR. Crystal structures of the shark E06 and its humanized variant (huE06 v1.1) in complex with human serum albumin (HSA) were determined at 3- and 2.3-Å resolution, respectively. The huE06 v1.1 molecule retained all but one amino acid residues involved in the binding site for HSA. Structural analysis of these V-NARs has revealed an unusual variable domain-antigen interaction. E06 interacts with HSA in an atypical mode that utilizes extensive framework contacts in addition to complementarity-determining regions that has not been seen previously in V-NARs. On the basis of the structure, the roles of various elements of the molecule are described with respect to antigen binding and V-NAR stability. This information broadens the general understanding of antigen recognition and provides a framework for further design and humanization of shark IgNARs.

Spine-based ageing methods in the spiny dogfish shark, Squalus suckleyi: How they measure up

The second dorsal spine has historically been used for age determination in the spiny dogfish shark. The dorsal spines are located on the external surface of the body and are subjected to natural wear and breakage. Two methods have been developed to account for the worn portion of the spine and extrapolate the lost annuli. We compared the performance of these methods using a large data collection assembled from multiple sources, and evaluated their utility for stock assessment and management of the spiny dogfish shark Squalus suckleyi in the Northeast Pacific Ocean. Our results showed that the two methods produced very different age estimates for older fish with worn spines. Both methods raised significant questions about some aspects of the age estimates produced, and further exploration of techniques to account for worn spine annuli is needed. It is therefore important to develop alternative methods for shark age determination, including those using stained vertebrae.

SPINY DOGFISH SAVES UREA FOR REUSE

![][1] Dogfish sharks can go for weeks without eating but when they do finally eat something, as for the rest of us, their digestive system kick-starts into action. Previous studies have shown that levels of Na+, Cl− and K+ ions and urea – osmolytes that play a role in fluid

An in vitro study of urea, water, ion and CO2/HCO3− transport in the gastrointestinal tract of the dogfish shark (Squalus acanthias): the influence of feeding

In vitro gut sac preparations made from the cardiac stomach (stomach 1), pyloric stomach (stomach 2), intestine (spiral valve) and colon were used to examine the impact of feeding on transport processes in the gastrointestinal tract of the dogfish shark. Preparations were made from animals that were euthanized after 1-2 weeks of fasting, or at 24-48 h after voluntary feeding on a 3% ration of teleost fish (hake). Sacs were incubated under initially symmetrical conditions with dogfish saline on both surfaces. In comparison to an earlier in vivo study, the results confirmed that feeding caused increases in H(+) secretion in both stomach sections, but an increase in Cl(-) secretion only in stomach 2. Na(+) absorption, rather than Na(+) secretion, occurred in both stomach sections after feeding. All sections of the tract absorbed water and the intestine strongly absorbed Na(+) and Cl(-), regardless of feeding condition. The results also confirmed that feeding increased water absorption in the intestine (but not in the colon), and had little influence on the handling of Ca(2+) and Mg(2+), which exhibited negligible absorption across the tract. However, K(+) was secreted in the intestine in both fasted and fed preparations. Increased intestinal water absorption occurred despite net osmolyte secretion into the mucosal saline. The largest changes occurred in urea and CO2/HCO3(-) fluxes. In fasted preparations, urea was absorbed at a low rate in all sections except the intestine, where it was secreted. Instead of an increase in intestinal urea secretion predicted from in vivo data, feeding caused a marked switch to net urea absorption. This intestinal urea transport occurred at a rate comparable to urea reabsorption rates reported at gills and kidney, and was apparently active, establishing a large serosal-to-mucosal concentration gradient. Feeding also greatly increased intestinal CO2/HCO3(-) secretion; if interpreted as HCO3(-) transport, the rates were in the upper range of those reported in marine teleosts. Phloretin (0.25 mmol l(-1), applied mucosally) completely blocked the increases in intestinal urea absorption and CO2/HCO3(-) secretion caused by feeding, but had no effect on Na(+), Cl(-) or water absorption.

Acid and base secreting cells in leopard shark (Triakis semifasciata) gills: mitochondrial richness, ATPase specificity, and vacuolar H+ ATPase (VHA) translocation

Sharks maintain stable blood pH by way of acid and base secreting cells in the gill. Using immunofluorescence, we confirmed the existence of two distinct gill cell types characterized by large abundance of either: vacuolar H+ ATPase (VHA) or Na+/K+ ATPase. Further analysis using antibodies against complex IV, confirmed that both cell types are also mitochondria rich. In VHA‐rich gill cells from dogfish sharks (Squalus acanthias) VHA moves from cytoplasmic vesicles to the basolateral membrane in order to rectify blood alkalosis experienced post feeding by pumping protons into alkaline blood. We observed similar VHA translocation occurs in fed leopard sharks. Western blot analyses showed a comparatively greater concentration of VHA in the membrane fraction of fed sharks over starved sharks. Western blots of gill crude homogenate fractions showed steady amounts of VHA, suggesting that the increased VHA content in the membrane of fed sharks result from translocation as opposed to generation of new gill cells with high membrane VHA content. VHA immunofluorescence microscopy of gill sections confirmed that fed sharks have more basolaterally located VHA. Because this phenomenon occurs in both leopard and dogfish sharks, the results suggest that VHA translocation may be a universal mechanism for combating blood alkalosis in marine elasmobranchs. Research was funded by the American Physiological Society UGSR Fellowship to Christian Munévar, the San Diego Fellowship to Jinae N. Roa, and Scripps Startup Funds to Martin Tresguerres.

Pattern and polarity in the development and evolution of the gnathostome jaw: Both conservation and heterotopy in the branchial arches of the shark, Scyliorhinus canicula

The acquisition of jaws constitutes a landmark event in vertebrate evolution, one that in large part potentiated their success and diversification. Jaw development and patterning involves an intricate spatiotemporal series of reciprocal inductive and responsive interactions between the cephalic epithelia and the cranial neural crest (CNC) and cephalic mesodermal mesenchyme. The coordinated regulation of these interactions is critical for both the ontogenetic registration of the jaws and the evolutionary elaboration of variable jaw morphologies and designs. Current models of jaw development and evolution have been built on molecular and cellular evidence gathered mostly in amniotes such as mice, chicks and humans, and augmented by a much smaller body of work on the zebrafish. These have been partnered by essential work attempting to understand the origins of jaws that has focused on the jawless lamprey. Chondrichthyans (cartilaginous fish) are the most distant group to amniotes within extant gnathostomes, and comprise the crucial clade uniting amniotes and agnathans; yet despite their critical phylogenetic position, evidence of the molecular and cellular underpinnings of jaw development in chondrichthyans is still lacking. Recent advances in genome and molecular developmental biology of the lesser spotted dogfish shark, Scyliorhinus canicula, make it ideal for the molecular study of chondrichthyan jaw development. Here, following the ‘Hinge and Caps' model of jaw development, we have investigated evidence of heterotopic (relative changes in position) and heterochronic (relative changes in timing) shifts in gene expression, relative to amniotes, in the jaw primordia of S. canicula embryos. We demonstrate the presence of clear proximo-distal polarity in gene expression patterns in the shark embryo, thus establishing a baseline molecular baüplan for branchial arch-derived jaw development and further validating the utility of the ‘Hinge and Caps’ model in comparative studies of jaw development and evolution. Moreover, we correlate gene expression patterns with the absence of a lambdoidal junction (formed where the maxillary first arch meets the frontonasal processes) in chondrichthyans, further highlighting the importance of this region for the development and evolution of jaw structure in advanced gnathostomes.

Specializations of intercellular junctions are associated with the presence and absence of hair cell regeneration in ears from six vertebrate classes

Sensory hair cell losses lead to hearing and balance deficits that are permanent for mammals, but temporary for nonmammals because supporting cells in their ears give rise to replacement hair cells. In mice and humans, vestibular supporting cells grow exceptionally large circumferential F-actin belts and their junctions express E-cadherin in patterns that strongly correlate with postnatal declines in regeneration capacity. In contrast, chicken supporting cells retain thin F-actin belts throughout life and express little E-cadherin. To determine whether the junctions in chicken ears might be representative of other ears that also regenerate hair cells, we investigated inner ears from dogfish sharks, zebrafish, bullfrogs, Xenopus, turtles, and the lizard, Anolis. As in chickens, the supporting cells in adult zebrafish, Xenopus, and turtle ears retained thin circumferential F-actin belts and expressed little E-cadherin. Supporting cells in adult sharks and bullfrogs also retained thin belts, but were not tested for E-cadherin. Supporting cells in adult Anolis exhibited wide, but porous webs of F-actin and strong E-cadherin expression. Anolis supporting cells also showed some cell cycle reentry when cultured. The results reveal that the association between thin F-actin belts and low E-cadherin is shared by supporting cells in anamniotes, turtles, and birds, which all can regenerate hair cells. Divergent junctional specializations in supporting cells appear to have arisen independently in Anolis and mammals. The presence of webs of F-actin at the junctions in Anolis appears compatible with supporting cell proliferation, but the solid reinforcement of the F-actin belts in mammals is associated with its absence.

A perfusion study of the handling of urea and urea analogues by the gills of the dogfish shark (Squalus acanthias)

The branchial mechanism of urea retention in elasmobranchs was investigated using an in vitro isolated-perfused head preparation, as well as in vivo samples, in the spiny dogfish shark. Both in vivo and in control saline perfusions containing 350 mmol L−1 urea, calculated intracellular urea concentrations in gill epithelial cells were close to extracellular concentrations. Urea efflux to the external water fell only non-significantly, and calculated gill intracellular urea concentration did not change when perfusate urea concentration was reduced from 350 to 175 mmol L−1 with osmotic compensation by 175 mmol L−1 mannitol. However, when the urea analogues thiourea or acetamide were present in the perfusate at concentrations equimolar (175 mmol L−1) to those of urea (175 mmol L−1), urea efflux rates were increased 4-fold and 6.5-fold respectively, and calculated gill intracellular urea concentrations were depressed by about 55%. Analogue efflux rates were similar to urea efflux rates. Previous studies have argued that either the basolateral or apical membranes provided the limiting permeability barrier, and/or that a back-transporter on the basolateral membranes of gill cells is responsible for urea retention. The present results provide new evidence that the apical membrane is the limiting factor in maintaining gill urea impermeability, and raise the prospect that a urea back-transporter, which can be competitively inhibited by thiourea and acetamide, operates at the apical membrane.

Spatio-temporal expression patterns of anterior Hox genes during Nile tilapia (Oreochromis niloticus) embryonic development

Hox genes encode transcription factors that function to pattern regional tissue identities along the anterior-posterior axis during animal embryonic development. Divergent nested Hox gene expression patterns within the posterior pharyngeal arches may play an important role in patterning morphological variation in the pharyngeal jaw apparatus (PJA) between evolutionarily divergent teleost fishes. Recent gene expression studies have shown the expression patterns from all Hox paralog group (PG) 2–6 genes in the posterior pharyngeal arches (PAs) for the Japanese medaka (Oryzias latipes) and from most genes of these PGs for the Nile tilapia (Oreochromis niloticus). While several orthologous Hox genes exhibit divergent spatial and temporal expression patterns between these two teleost species in the posterior PAs, several tilapia Hox gene expression patterns from PG3-6 must be documented for a full comparative study. Here we present the spatio-temporal expression patterns of hoxb3b, c3a, b4a, a5a, b5a, b5b, b6a and b6b in the neural tube and posterior PAs of the Nile tilapia. We show that several of these tilapia Hox genes exhibit divergent expression patterns in the posterior PAs from their medaka orthologs. We also compare these gene expression patterns to orthologs in other gnathostome vertebrates, including the dogfish shark.

Antimicrobial and Lytic Activities of Squalamine Analogs: Effect of Varied Cationic Groups at C3 and Stereochemistry at C7

Squalamine (3β-N-1-{N-[3-(4-aminobutyl)]-1,3-diaminopropane}-7α,24R-dihydroxy-5α-cholestane-24-sulfate), an aminosterol from the dogfish shark (Squalus acanthias), is a potent antimicrobial compound believed to act through plasma membrane lysis. In this report, the antimicrobial activity of squalamine, several structurally related analogs, and bile acid based aminosterols are characterized using two different assays. The structurally similar analogs vary in the stereochemistry at the 3- and 7- substitutents, and also in the length and composition of the polyamine added at C-3. The bile acid analogs are generated by the addition of diaminopropane to C-3 of common bile acid methyl esters. The antimicrobial activity of the analogs was assessed against four bacterial strains. Membrane lytic activity was assayed using large unilamellar vesicles encapsulating a fluorescent calcein dye. Both vesicle lysis and antimicrobial activity of the aminosterols are shown to improve with more cationic groups on the polyamine substituent at C-3. Also, analogs with a 7α-OH substitutent are more effective than their 7β-OH analogs. The bile acid analogs were significantly less active than squalamine.The results suggest that the stereochemistry of the C7-OH group and the A/B ring junction is important in aminosterol activation at the membrane surface.

Demersal fishes caught with bottom gillnets and baited gears at 500-2800m on the continental slope off Nova Scotia, Canada

Fishing trials with bottom fixed gears (primarily gillnets but also shrimp and crab traps and longlines) were conducted on the continental slope off Nova Scotia in August 1991. Fishing was conducted at several depths between 500 and 2800 m in two areas, one on the open slope south of Emerald Bank and the other at the mouth of The Gully, a large canyon. Catches by gillnets accounted for about 90% of the total and were predominated by deepwater chimaera (Hydrolagus affinis), black dogfish (Centroscyllium fabricii) and Portuguese shark (Centroscymnus coelolepis). The most frequently caught species in traps were snubnose eel (Simenchelys parasitica) and abyssal grenadier (Coryphaenoides armatus). Variations in catches by depth and area are described, and comparisons are made with catches from otter trawl surveys at similar depths with regard to the most prominent species caught and their size compositions.