Squalus Acanthias Research Articles

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.

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 (20min), and the same parameters were monitored for the subsequent 4h of recovery. While MO2 nearly doubled immediately after exercise and remained elevated for 2h, ventilation dynamics did not change, suggesting that fish were increasing oxygen extraction efficiency at the gills. Diffusive water flux rates (measured over 0-2h of recovery) were not affected. Ammonia losses were elevated by 7.6-fold immediately after exercise and remained elevated for 3h into recovery, while urea-N losses were elevated only 1.75-fold and returned to control levels after 1h. 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 urea‑nitrogen may be vital to maintaining nitrogen balance in these fish.

Strategic importance of the Bergen‐Shetland Corridor to marine biology and oceanography of the Atlantic Ocean

AbstractThe North Sea is one of the busiest and most exploited marine areas on Earth and is home to many highly migratory and economically important species. At the northern boundary, a 300‐km corridor between Norway and Shetland forms a major egress point from the North Sea to the Norwegian Sea and broader Atlantic Ocean, which is known to be used by many focal species including Atlantic salmon, European eel, European sturgeon, Atlantic bluefin tuna, basking shark, Atlantic mackerel, spiny dogfish, among others. We argue that this relatively shallow 300‐km corridor is a critical area for ecological and oceanographic research in the North Sea to understand species distribution, migratory patterns, responses to climate, fisheries, and more. Instrumentation of the Bergen‐Shetland Corridor with a line of oceanographic and biological tracking infrastructure would help capture the spatiotemporal dynamics of the ocean and its major fauna between the North Sea and Norwegian Sea, a boundary between management areas from ICES and OSPAR.

Squalamine and Its Aminosterol Derivatives: Overview of Biological Effects and Mechanisms of Action of Compounds with Multiple Therapeutic Applications.

Squalamine is a natural aminosterol that has been discovered in the tissues of the dogfish shark (Squalus acanthias). Studies have previously demonstrated that this promoter compound and its derivatives exhibit potent bactericidal activity against Gram-negative, Gram-positive bacteria, and multidrug-resistant bacteria. The antibacterial activity of squalamine was found to correlate with that of other antibiotics, such as colistin and polymyxins. Still, in the field of microbiology, evidence has shown that squalamine and its derivatives have antifungal activity, antiprotozoa effect against a limited list of protozoa, and could exhibit antiviral activity against both RNA- and DNA-enveloped viruses. Furthermore, squalamine and its derivatives have been identified as being antiangiogenic compounds in the case of several types of cancers and induce a potential positive effect in the case of other diseases such as experimental retinopathy and Parkinson’s disease. Given the diverse effects of the squalamine and its derivatives, in this review we provide the different advances in our understanding of the various effects of these promising molecules and try to draw up a non-exhaustive list of the different mechanisms of actions of squalamine and its derivatives on the human organism and on different pathogens.

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.

Sustained endocrine and exocrine function in the pancreas of the Pacific spiny dogfish post-feeding.

Secretions of the exocrine pancreas contain digestive enzymes integral to the digestive process. The Pacific spiny dogfish (Squalus suckleyi) has a discrete pancreas, divided into two lobes termed the dorsal and ventral lobes. These lobes drain into the anterior intestine via a common duct to enable digestion. Previous studies have identified that the exocrine pancreas produces (co)lipases, chymotrypsin, carboxypeptidase, and low levels of chitinases; however, investigations into other digestive enzymes are limited. We detect the presence of lipase, trypsin, and carbohydrase and show that activities are equivalent between both lobes of the pancreas. Additionally, we sought to investigate the influence of a single feeding event (2% body weight ration of herring by gavage) on enzyme activities over an extended time course (0, 20, 48, 72, 168h) post-feeding. The results indicate that there are no differences in pancreatic tissue digestive enzyme activities between fed or fasted states. Analysis of acinar cell circumference post-feeding demonstrates a significant increase at 20 and 48h, that returns to fasting levels by 72h. No significant changes were observed regarding whole-tissue insulin or glucagon mRNA abundance or with glucose transporter (glut) 1 or 3. Yet, a significant and transient decrease in glut4 and sodium glucose-linked transporter mRNA abundance was found at 48h post-feeding. We propose that the constant enzyme activity across this relatively large organ, in combination with a relatively slow rate of digestion leads to an evenly distributed, sustained release of digestive enzymes regardless of digestive state.

Sensational shark skin and dazzling dermal denticles

Shark skin has a unique structure which has served as a source of inspiration for engineers interested in reducing drag in water or preventing parasites from becoming attached. The skin is covered in tooth-like structures called dermal denticles, made of an enamel-type tissue and dentine on the outermost portion and containing a central cavity filled with pulp. Their general shape is similar to a pointy canine tooth where the base is wider than the edge and is thought to reduce the amount of drag pulling on the animal when moving through water. Interestingly, previous work suggests a wide range of denticle shapes on the skin around the gills of dogfish, where the denticles closer to the head are rounded and smooth compared with the ridged and sharp denticles toward the tail. But does this diversity in denticle shape near the gills also occur in other shark species? And what purpose might these different shapes serve?To study these questions, Molly Gabler-Smith and George Lauder from Harvard University, USA, Dylan Wainwright from Yale University, USA, and colleagues from Harvard University compared the shape and size of the denticles around the gills of 13 shark species with various lifestyles. They aimed to better understand whether the shape of these denticles differs between species and whether these differences might help water to flow over the gills.The researchers collected the sharks from fishing surveys and museums, ranging from the thresher shark, known for its massive tail, enabling it to jump out of water like a dolphin, to the spiny dogfish, which are smaller and known to live in deep sea beds. They then took 3D measurements of denticle length and width and used electron and light microscopy to look at differences in denticle shape across the skin around the gills of individual sharks and between different species.Comparing the structures, it turned out that the denticle shape varied across different areas of the skin surrounding the gills in all of the species, with the short broad denticles arranged toward the front of the shark and longer, pointier denticles occurring toward to the tail of the shark. In fact, the denticles found closer to the tail had pronounced ridges on their surfaces and three spiky spines, in contrast to the smoother almond-shaped denticles found towards the head. Some species, such as the chain catshark, had extreme changes in denticle shape over a distance of a few millimeters. They also found that the shark species that continuously swim to breathe had larger denticles toward the head compared with shark species that breathe by opening and closing their mouths to pump water over the gills.The extreme differences in shape between the denticles found towards the head versus those toward the tail may serve to reduce friction and prevent damage to the skin when the gills flap against each other while breathing. The dramatic shape difference may also reduce drag from water moving through the gills, which could prevent water from flowing in the opposite direction, stopping the shark from getting enough oxygen from the water. This study gives us a foundation for future research on how denticle shape can help sharks to breathe and if there are differences in how water moves over the denticles surrounding the gills of active or passively breathing species. Understanding the great diversity and function of denticles in shark skin can help us to learn how they evolved and even allow us to better imitate their amazing ability to reduce drag in water.

Over 120 years of landing trends in Japan, for the commercially exploited shark species, Squalus suckleyi

Landing trends denote actual removal of a species by fisheries and may be a useful index of stock biomass dynamics, but accurate records for North Pacific spiny dogfish (Squalus suckleyi) landings in Japan are only available for 1952–1967. We used official Japan statistical yearbook data and bootstrap methodology to estimate landings of Pacific spiny dogfish, for 1894–1951 and 1968–2013, by prefecture. The landing estimates indicate that this species has been continuously exploited around Japan for over 120 years, since at least 1894. The landing trends could be divided into four periods: stable, low catch (1894–1919); increasing catch (1920–1949); decreasing catch (1950–1963); and relative stability (1964–2013). The trend in Pacific spiny dogfish landings appears to have been strongly influenced by societal demand, as supported by unit price trends for sharks. This result suggests that determinations of stock status based only on landing trends are inadequate for this species. After 1990, estimates of Pacific spiny dogfish landings ranged from 2800 to 4500 mt annually. A large proportion (52.7–74.7%) of the annual landings of this species were made by Hokkaido and Aomori prefectures, which are located near important habitat for this species in the northwestern Pacific. Thus, these regions are especially important for effective management and sustainable exploitation of the Pacific spiny dogfish stock in Japan.

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.

Aquaporin (AQP) channels in the spiny dogfish, Squalus acanthias I: Characterization of AQP3 and AQP15 function and expression, and localization of the proteins in gill and spiral valve intestine.

Complementary DNAs (cDNAs) for two aquaporin water channel genes (AQP3 and AQP15) were amplified cloned and sequenced to initiate this study. Northern blot analysis was carried out to confirm the mRNA sizes of these AQP genes with AQP3 mRNA bands exhibiting sizes of 1.2 and 1.6k bases and AQP15 had a mRNA band of 2.1k bases. Northern blot analysis was also performed on kidney and esophagus total RNA samples from fish acclimated to 75%, 100% or 120% seawater (SW). The level of AQP15 mRNA expression was shown to significantly decrease following salinity acclimation from 100 to 120% SW. An opposite but non-significantly different trend was observed for AQP3 mRNA levels. Full length cDNAs were then used to generate AQP3 and AQP15 mRNAs for microinjection into Xenopus oocytes. Both AQP3- and AQP15- microinjected oocytes exhibited significantly elevated apparent water permeability compared to control oocytes at neutral pH. The apparent water permeability was mercury-inhibitable, significantly so in the case of AQP3. AQP3 microinjected oocytes showed pH sensitivity in their apparent water permeability, showing a lack of permeability at acidic pH values. The Carboxyl-terminal derived amino acid sequences of AQP3 and AQP15 were used to generate rabbit affinity-purified polyclonal antibodies. Western blots with the antibodies showed a band of 31.3kDa for AQP3 in the kidney, with minor bands at 26, 24 and 21kDa. For AQP15 a band of 26kDa was seen in gill and kidney. Fainter bands at 28 and 24kDa were also seen in the kidney. There was also some higher molecular weight banding. None of the bands were seen when the antibodies were pre- blocked with their peptide antigens. Immunohistochemical localization studies were also performed in the gill and spiral valve intestine. In the gill, AQP15 antibody staining was seen sporadically in the membranes of surface epithelial cells of the secondary lamellae. Tyramide amplification of signals was employed in the spiral valve intestine. Tyramide-amplified AQP3 antibody staining was observed in the basal membrane of the invaginated epithelial cell layer of secondary intestinal folds in luminal surface of either the side wall of the spiral valve intestine or in internal valve tissue 'flaps'. For the AQP15 antibody, tyramide-amplified staining was instead found on the apical and to a lesser extent the lateral membranes of the same invaginated epithelial cell layer. The localization of AQP3 and AQP15 in the spiral valve intestine suggests that a trans-cellular water absorption pathway may exist in this tissue.

Of three sharks and one chimaera: varied habitat preferences across a latitudinal range revealed by coastal and offshore surveys.

Using national and international research survey data and applying a combination of models and mapping tools, this study revealed temperature and depth as the crucial environmental drivers of both the distribution and the abundance of four benthopelagic chondrichthyans inhabiting Norwegian and Icelandic waters: rabbitfish (Chimaera monstrosa), velvet-belly lanternshark (Etmopterus spinax), blackmouth catshark (Galeus melastomus) and spurdog (Squalus acanthias). C. monstrosa and E. spinax seem to prefer similar spatial and ecological habitats, that is deep and cold waters. In contrast, G. melastomus and S. acanthias both prefer similar ecological habitats, that is warmer and shallower waters; nonetheless, they exhibit a different spatial distribution pattern. The species' varied habitat and spatial preferences may lead to different levels of exposure to fishing activities and associated by-catch risks. Findings of the species' spatial distributions and their driving forces are expected to inform the sustainable management of these species and the ecosystems they inhabit.

Leopard Seals (Hydrurga leptonyx) in New Zealand Waters Predating on Chondrichthyans

Leopard seals (Hydrurga leptonyx) are top-order predators that prey on a wide variety of species including crustaceans, cephalopods, fishes, birds, and pinnipeds. While multiple diet studies have been conducted worldwide, there are no previous accounts of leopard seals predating on chondrichthyans. As part of a wider study on the diet of leopard seals in New Zealand (NZ) waters, researchers and citizen scientists recorded 39 observations of predation and collected 127 scats (166 total records) between 1942 and 2019. Predation on chondrichthyans was detected in 23.1% (n = 9) of observations of predation and 7.1% (n = 9) of scats (the latter via morphological examination and DNA sequencing). From both observations of predations and scats, three chondrichthyan species or genus were identified; elephantfish (Callorhinchus milii), ghost sharks (Hydrolagus spp.) and spiny dogfish (Squalus acanthias). While this is the first published record of leopard seals feeding on chondrichthyans, the relatively high frequency of occurrence within our NZ records, and that certain individuals appeared to target this type of prey, indicates that these species could constitute a substantial, or important, part of the diet for some leopard seals in this region. As chondrichthyans form an important part of the NZ marine ecosystems, our recognition of an additional top-order predator of these species contributes to understanding the overall health of, and future impacts of predators on, the wider NZ marine ecosystem.

The use of fishers’ Local Ecological Knowledge to reconstruct fish behavioural traits and fishers’ perception of conservation relevance of elasmobranchs in the Mediterranean Sea

The Mediterranean Sea has a long-lasting history of fishery exploitation that, together with other anthropogenic impacts, has led to declines in several marine organisms. In particular, elasmobranch populations have been severely impacted, with drastic decreases in abundance and species diversity. Based on their experience, fishers can provide information on marine species occurrence, abundance and behavioural traits on a long-term scale, therefore contributing to research on the poorly studied biological aspects of elusive or rare elasmobranch species. In this study, for the first time, the use of the Local Ecological Knowledge (LEK) of fishers was applied to study the behavioural traits of sharks, rays and skates in 12 FAO-GFCM geographical sub-areas (GSAs) of the Mediterranean Sea. This study found both new insight and proved the reliability of LEK-based catch seasonality, reflecting seasonal movements, by comparing LEK-based findings and available literature on five elasmobranch taxa (Mustelus spp., Squalus acanthias, Raja spp., Myliobatis aquila and Scyliorhinus stellaris) in the Adriatic Sea and 7 taxa (Mustelus spp., Raja spp., Prionace glauca, Scyliorhinus canicula, Torpedo spp., Pteroplatytrygon violacea and Isurus oxyrinchus) in the remaining Mediterranean GSAs. In addition, LEK provided new insights into a novel comprehensive representation of species aggregations (Mustelus spp., S. acanthias, M. aquila and S. canicula) in the sampled GSAs and supplied the first descriptions of the size, number of individuals and sex composition of the aggregations. When the limits and shortcomings of LEK-based research are considered, this methodology can be a complementary and cost-effective tool used to study elasmobranchs in either a data-poor scenario or a scenario in which a baseline is missing. LEK can also be useful for the evaluation and inclusion of fishers’ perceptions on bottom-up management and to provide important evidence for conservation plans.

Red and white muscle proportions and enzyme activities in mesopelagic sharks.

In the last decade, there has been an increase in the study of the ecology of deep-sea organisms. One way to understand an organism's ecology is the study of its metabolism. According to literature, deep-sea sharks possess a lower anaerobic enzyme activity than their shallow-water counterparts, but no difference has been observed regarding their aerobic enzyme activities. These studies have suggested deep-sea sharks should be slow and listless swimmers. However, other studies based on video observations have revealed differences in cruise swimming speed between different species. The present study examined muscles of squaliform sharks, including both luminous and non-luminous species. We combined measurements of the relative amounts of red and white muscle with assays of enzymes that are used as markers for aerobic (citrate synthase, malate dehydrogenase) and anaerobic (lactate dehydrogenase) metabolism, searching for a relationship with cruising speeds. Non-luminous deep-sea species displayed lower aerobic enzyme activities but similar anaerobic enzyme activities than the benthic shallow-water counterpart (Squalus acanthias). Conversely, luminous Etmopteridae species were found to have similar aerobic enzyme activities to S. acanthias but displayed lower anaerobic enzyme activities. Analyses revealed that red muscle proportion and aerobic enzyme activities were positively related to the cruise swimming speed. In contrast, Dalatias licha, which swims at the slowest cruise swimming speed ever recorded, presented a very low aerobic metabolic phenotype (lower aerobic marker enzymes and less red muscle). Finally, the values obtained for white muscle proportion and anaerobic metabolic phenotype suggested a high burst capacity for D. licha and non-luminous sharks.

Development and characterization of fish gelatin-based biodegradable film enriched with Lepidium sativum extract as active packaging for cheese preservation

The physical and functional properties of gelatin-based films enriched with organic extracts from Lepidium sativum seeds were studied. Gelatin was extracted from the skin of dogfish (Squalus acanthias) and the functional gelatin-based films were used to preserve cheese during chilled storage. Ethanol extract (LSE3) and gelatin-based film enriched with LSE3 at 20 μg/mL showed high antioxidant potential using various complementary methods. No significant difference was measured in the mechanical parameters of the enriched films in terms of thickness, tensile strength and elongation at break. LSE3 incorporation at the highest level slighltly decreased the film L∗ value from 90.30 ± 0.10 to 88.10 ± 0.12, while the b∗ value increased from 0.91 ± 0.07 to 8.89 ± 0.12. Wrapping the cheese with gelatin-based film enriched with 20 μg LSE3/mL reduced the syneresis by 40% and stabilized the color, peroxidation and bacteria growth as compared to the unwrapped sample after 6 days of storage. In addition, cheese wrapped with the active gelatin-based film showed the lowest changes in texture parameters. Overall results suggest the use of the enriched gelatin film as active packaging material to preserve cheese quality.

Gastric Evacuation Rates of Spiny Dogfish, Goosefish, and Summer Flounder: Implications for Multispecies Models

AbstractThe gastric evacuation rates of Spiny Dogfish Squalus acanthias, Summer Flounder Paralichthys dentatus and Goosefish Lophius americanus held at two different temperatures were determined in the laboratory by gastric lavage. Overall, exponential models provided the best fit for the evacuation rates. The Spiny Dogfish, an elasmobranch, evacuated more slowly than the Summer Flounder (a teleost) but the Goosefish, also a teleost, had the slowest evacuation rate of the three species. The Goosefish evacuation rate was nearly ten times slower than that of Summer Flounder. Evacuation was more rapid at the higher temperature tested in all three species. At 15°C, Summer Flounder had the highest average evacuation rate (0.094 exponential rate of decline), followed by Spiny Dogfish (0.063 exponential rate of decline), and then Goosefish (0.018 exponential rate of decline). Among the three species, activity levels and feeding behaviors are also very different, contributing to differences in evacuation rate. Species‐specific parameters of evacuation rate should be considered to better inform multispecies and ecosystem models and to more accurately estimate consumption and prey removal rather than using broad taxonomic groupings as in current common practice.

A closer look at the bycatch of medium‐sized and large sharks in the northern Catalan coast (north‐western Mediterranean Sea): Evidence of an ongoing decline?

Abstract Historically, the Mediterranean Sea supported a rich shark fauna. Presently, however, populations of most shark species have significantly declined, largely due to intense fishing pressure. Interviews with crew members of bottom trawlers, drifting longliners and bottom longliners operating off the Costa Brava (Catalonia, NE Spain) were conducted between October 2016 and July 2017 in order to gather information on the current bycatch rate of several shark species. Interviews covered 41.2% of the fleet and respondents were asked for the bycatch of selected shark species—Alopias vulpinus, Cetorhinus maximus, Galeorhinus galeus, Hexanchus griseus, Isurus oxyrinchus, Mustelus spp., Prionace glauca, and Squalus acanthias—in two distinct time periods. Bottom trawlers captured the highest diversity of species (eight) followed by bottom longliners (seven), and drifting longliners (three). Most respondents (89.7%) declared having captured at least one shark from 2006 to 2016 but only 56.4% declared having captured at least one shark from 2016 to 2017. From 2016 to 2017, the whole fleet captured 89 specimens of H. griseus (95% confidence interval (CI) = 145, 34), 14 of G. galeus (95% CI = 30, 0), 3 of A. vulpinus (95% CI = 8, 0), 3 of I. oxyrinchus (95% CI = 8, 0), 3 of C. maximus (95% CI = 6, 0), and no Mustelus spp. The total bycatch of P. glauca and S. acanthias was uncertain due to extremely loose confidence intervals. A significant decline was perceived by fishermen in the bycatch of C. maximus and S. acanthias, whereas the bycatch of H. griseus was considered to have remained stable. This study suggests a dramatic reduction in the abundance of most of the medium‐sized and large sharks of the Costa Brava and the likely disappearance of Mustelus spp. from the area. Only H. griseus, S. acanthias, and P. glauca are still being bycaught frequently.

A redescription of the appendicular skeleton of Squalus acanthias (Elasmobranchii: Squaliformes: Squalidae)

AbstractThe anatomy of Squalus acanthias has been explored and investigated for the past 150 years. Despite being a relatively well‐known species, some anatomical inaccuracies on the paired fins persist throughout the literature, such as the presence of suprascapular cartilages and the morphology of the articular region of the pectoral fin. This study reassesses and provides new descriptions of the paired fins of Squalus acanthias, including comparisons with other representatives of Squalidae, aimed to expand the anatomical information of these species. All examined species of Squalus have two sites in the scapulocoracoid for the articulation of the pectoral basals: one facet articulating with the propterygium and a condyle for the mesopterygium (or both meso‐ and metapterygium). Additionally, the scapulocoracoid does not have a scapular process. Squalus acanthias is unique for having a series of barrel‐shaped elements in the anterior region of the scapula. These elements are lacking in all other examined species of Squalus and Cirrhigaleus (and sharks in general) and are likely an autapomorphy of S. acanthias.

Evaluation of the comprehensive feeding strategy and trophic role of overexploited mesopredator species in the Sea of Marmara (northeastern Mediterranean)

Mesopredator species play an essential role in balancing and sustaining ecosystems through their interactions with various species and with their habitats. In ecosystems that have been subjected to overfishing, it is essential to obtain information on the trophic ecology of such predators. Based on this motivation, this study aimed to investigate the feeding strategies and trophic roles of four demersal sharks (e.g., Mustelus mustelus, Mustelus asterias, Squalus acanthias, and Scyliorhinus canicula) by analyzing their stomach contents and using stable isotope (δ13C and δ15N) analysis. These shark species are subject to overfishing, and their landings have decreased by 98% over the last 18 years in the Sea of Marmara. The results demonstrated that interspecific differences in the main prey resources exist among those sharks. Mustelus mustelus and Mustelus asterias feed mainly on crustaceans, and their diets are very similar. However, Mustelus asterias utilizes a specialist feeding strategy while Mustelus mustelus utilizes a medium-state generalist strategy. Squalus acanthias occupies a high trophic level and mainly feeds on teleosts over both short and long time scales. The probability of isotopic niche overlap of Scyliorhinus canicula with the isotopic niches of S. acanthias was the highest (70.7%), which indicates that both species exploit similar food resources within the same environment. These results contribute to the knowledge of the ecological role of these highly vulnerable cartilaginous species and may help to improve conservation programs in the Sea of Marmara, a lesser-known part of the northeast Mediterranean.