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This updated checklist of chondrichthyans from the Gulf of California (GC) with notes on zoogeography, conservation status, and commercial value includes 2 subclasses, 14 orders, 31 families, 55 genera, and 106 species. Euselachii (Batomorphi 44.3% and Selachii 51.8%) is the most diverse subclass (13 orders, 29 families, 53 genera, and 102 species). The order Carcharhiniformes (4 families, 16 genera, and 36 species) and Myliobatiformes (6 families, 11 genera, and 24 species) represent 56.6% of the total cartilaginous fish diversity in the GC. Based on the analysis of biogeographic affinities, most species include their ranges of distribution into the “Sinus-Californian” (55.7%), Mexican (41.5%), and Panamic (36.8%) provinces; 29 species are circumtropical, 7 amphipacific, 5 amphiamerican, and 4 endemic. Based on the IUCN Red List, 1 species is “Critically Endangered,” 2 are “Endangered,” 14 are “Vulnerable,” 23 are “Near Threatened,” 26 are of “Least Concern,” 3 “Not Evaluated,” and 36 are “Data Deficient.” Mexican laws fully protect 9 species classified as “Threatened,” at “Risk of Extinction,” or under “Special Protection,” whereas the rest are protected from fishing at least during 3 months of the year. Thirty-seven species (35%) are of commercial value; another 30 (28%) rare species of low commercial importance have been reported in the catches of artisanal and semi-industrial fisheries during the last 2 decades. Sørensen's coefficient of similarity and cluster analysis between major faunal divisions in the GC suggest the existence of 2 large chondrichthyan assemblages for this region ([NGC-CGC] + [SGC]). This study increases to 106 the species richness of Chondrichthyes known in the GC and serves as the baseline for formulating and implementing of conservation programs for this group of cartilaginous fish. [ABSTRACT FROM AUTHOR]

The anatomy of sharks, rays, and chimaeras (chondrichthyans) is crucial to understanding the evolution of the cranial system in vertebrates due to their position as the sister group to bony fishes (osteichthyans). Strikingly different arrangements of the head in the two constituent chondrichthyan groups—holocephalans and elasmobranchs—have played a pivotal role in the formation of evolutionary hypotheses targeting major cranial structures such as the jaws and pharynx. However, despite the advent of digital dissections as a means of easily visualizing and sharing the results of anatomical studies in three dimensions, information on the musculoskeletal systems of the chondrichthyan head remains largely limited to traditional accounts, many of which are at least a century old. Here, we use synchrotron tomographic data to carry out a digital dissection of a holocephalan and an elasmobranch widely used as model species: the elephantfish, Callorhinchus milii, and the small‐spotted catshark, Scyliorhinus canicula. We describe and figure the skeletal anatomy of the head, labial, mandibular, hyoid, and branchial cartilages in both taxa as well as the muscles of the head and pharynx. In Callorhinchus, we make several new observations regarding the branchial musculature, revealing several previously unreported or ambiguously characterized muscles, likely homologous to their counterparts in the elasmobranch pharynx. We also identify a previously unreported structure linking the pharyngohyal of Callorhinchus to the neurocranium. Finally, we review what is known about the evolution of chondrichthyan cranial muscles from their fossil record and discuss the implications for muscle homology and evolution, broadly concluding that the holocephalan pharynx is likely derived from a more elasmobranch‐like form which is plesiomorphic for the chondrichthyan crown group. This dataset has great potential as a resource, particularly for researchers using these model species for zoological research, functional morphologists requiring models of musculature and skeletons, as well as for palaeontologists seeking comparative models for extinct taxa. [ABSTRACT FROM AUTHOR]

Elasmobranch diets consist of high quantities of protein and lipids, but very low levels of carbohydrates including glucose. Reflecting this diet, most tissues use lipids and ketone bodies as their main metabolic fuel. However, the rectal gland has been shown to be dependent on glucose as a fuel, so we hypothesized that glucose transporters (GLUTs) would be present and upregulated in the gland during times of activation (e.g. following a meal). In this study, we searched for and identified putative class I GLUTs in three elasmobranchs and a holocephalan using transcriptomes, and used these to reconstruct a Bayesian phylogeny. We determined that each of the four species possessed three of the four class I GLUT sequences, but the identities of the isoforms present in each species differed between the elasmobranchs (GLUT1, 3 and 4) and the holocephalan (GLUT1, 2 and 3). We then used qPCR to measure mRNA levels of these GLUTs in the rectal gland, liver, intestine, and muscle of fed and starved spiny dogfish (Squalus suckleyi). The rectal gland data showed higher mRNA levels of GLUT4 in the starved relative to the fed fish. In the muscle, both GLUT1 and 4 were significantly elevated at 24 h post-feeding, as was the case for GLUT4 in the liver. In the intestine on the other hand, GLUT4 was significantly elevated by 6 h post-feeding, remaining elevated through 48 h. We suggest that GLUT4 has taken on the role of GLUT2 in elasmobranchs as the expression patterns observed in the liver and intestine are representative of GLUT2 in other vertebrates.

Chondrichthyans are usually caught incidentally in fisheries for species of high commercial value and then discarded on board or landed as by-products. On the coast of Chubut province and adjacent waters (43°00′S–44°56′S) a bottom trawl fishery has developed targeted at the Patagonian shrimp (Pleoticus muelleri) and common hake (Merluccius hubbsi). Since 2005, this fishery has been monitored by the On-board Observers Program of Chubut province (POBCh). With the aim of advancing towards an ecosystem approach, POBCh not only collects information about target species but also about all the species caught by the trawl nets of the province fisheries. From the information collected by this programme it was possible to identify and record the chondrichthyan species vulnerable to the fishing gear used by the coastal fleet that operates from Puerto Rawson. The composition of the fleet catch was characterized according to the target species during the 2005–2014 period. In the analysis of 3786 hauls, 23 species of chondrichthyans (seven species of sharks, 15 species of batoids and a single species of Holocephali) were identified. Seven species showed a frequency of occurrence greater than 10% (Callorhinchus callorynchus, Discopyge tschudii, Mustelus schmitti, Sympterygia bonapartii, Psammobatis normani, Squalus acanthias and Zearaja chilensis). Species spatial distribution was evaluated and five areas of species assemblages were established. Besides the aspects related to bycatch, these analyses have contributed to the knowledge of the chondrichthyan biodiversity in the provincial coast where the fleet operates, a region with incomplete and mostly dispersed and outdated information. [ABSTRACT FROM AUTHOR]

Holocephalans exhibit auxiliary appendages called pre-pelvic claspers (PPCs) that are located anterior to the pelvic fins, while pelvic claspers are pelvic fin modifications located posteriorly as modified metapterygia. Articulation points of the PPCs have not previously been imaged or evaluated in a comparative context, therefore, they may represent modified pelvic fin structures if they articulate with the propterygium. Alternatively, they could represent the only example of an independent third set of paired appendages in an extant taxon, if they articulate independently from any pelvic fin basal cartilages, challenging the current paradigm that extant jawed vertebrates are constrained to two sets of paired appendages. Two extinct groups, including Placoderms and Acanthodians, exhibit variation in the number of paired appendages, suggesting this may be a plesiomorphic trait. We evaluated PPC developmental growth rates, morphology, and articulation points in spotted ratfish (Hydrolagus Colliei, Holocephali). We also compared variation in PPC morphology among representatives of the three extant holocephalan families. Both, the pre-pelvic and pelvic claspers exhibit a dramatic surge in growth at sexual maturity, and then level off, suggesting synchronous development via shared hormonal regulation. While mature females are larger than males, pelvic fin growth and development is faster in males, suggesting a selective advantage to larger fins with faster development. Finally, microcomputed tomography scans revealed that PPCs are not modified propterygia, nor do they articulate with the propterygium. They articulate with the anterior pre-pelvic process on the anterior puboischiadic bar (or pelvic girdle), suggesting that while they are associated with the pelvic girdle, they may indeed represent a third, independent set of paired appendages in extant holocephalans., (© 2023 Wiley Periodicals LLC.)

The Carboniferous (358.9 to 298.9 Ma) saw the emergence of marine ecosystems dominated by modern vertebrate groups, including abundant stem-group holocephalans (chimaeras and relatives). Compared with the handful of anatomically conservative holocephalan genera alive today-demersal durophages all-these animals were astonishingly morphologically diverse, and bizarre anatomies in groups such as iniopterygians hint at specialized ecological roles foreshadowing those of the later, suction-feeding neopterygians. However, flattened fossils usually obscure these animals' functional morphologies and how they fitted into these important early ecosystems. Here, we use three-dimensional (3D) methods to show that the musculoskeletal anatomy of the uniquely 3D-preserved iniopterygian Iniopera can be best interpreted as being similar to that of living holocephalans rather than elasmobranchs but that it was mechanically unsuited to durophagy. Rather, Iniopera had a small, anteriorly oriented mouth aperture, expandable pharynx, and strong muscular links among the pectoral girdle, neurocranium, and ventral pharynx consistent with high-performance suction feeding, something exhibited by no living holocephalan and never clearly characterized in any of the extinct members of the holocephalan stem-group. Remarkably, in adapting a distinctly holocephalan anatomy to suction feeding, Iniopera is more comparable to modern tetrapod suction feeders than to the more closely related high-performance suction-feeding elasmobranchs. This raises questions about the assumed role of durophagy in the evolution of holocephalans' distinctive anatomy and offers a rare glimpse into the breadth of ecological niches filled by holocephalans in a pre-neopterygian world.

The growth rate, reproductive aspects, and natural mortality of chimaeras and ratfish are poorly known. In this study, life-history parameters for cockfish Callorhinchus callorhynchus (Holocephali-Callorhinchidae) are estimated, which is an important fish resource exploited in Chile. Specimens were sampled from the artisanal fishery captures, from November 2006 to November 2007. The standard length (SL) of males fluctuated between 20 and 62 cm, and between 21 and 70 cm for females. Von Bertalanffy growth parameters were estimated through length-frequency data analysis using MULTIFAN. The length-weight relationship and von Bertalanffy growth parameters were significantly different for males and females, as well as the length at 50% maturity. For males a model with 5 age-classes was the best, with asymptotic length L = 52 cm SL, growth coefficient K = 0.473 yr, and age at length zero t = −0.690 yrs. For females the best model was represented by 10 age-classes ( L = 70.3 cm SL, K = 0.193 yr, t = −1.158 yrs) in the length-frequency data sets. Length at 50% maturity of males was estimated in 43.7 cm SL, and in 50.2 cm SL for females. The natural mortality rate fluctuated between 0.42 and 0.82 yr for males and between 0.12 and 0.37 yr for females, depending upon the method used. It is concluded that C. callorhynchus is a species with life-history parameters significantly different between males and females, and such differences should be taken into account in future population dynamics analysis. [ABSTRACT FROM AUTHOR]

Abstract: The renin–angiotensin system is an enzyme-linked hormonal cascade that plays an important role in body fluid and cardiovascular regulation. The system is initiated by the action of renin on the precursor protein, angiotensinogen (AGT), whose sequence information is scarce because of its high variability among species. In the present study, we cloned AGT in chondrichthyans (elasmobranchs: Triakis scyllium, Dasyatis akajei, Leucoraja erinacea and a holocephalan: Callorhinchus milii). Homology was low among AGTs thus far identified; 25–28% between elasmobranchs and tetrapods and 33–61% even within chondrichthyans. All chondrichthyan angiotensin (ANG) II’s have a unique Pro3 instead of Val3 as seen in all other species. In addition, holocephalan ANG II has an unusual His4 instead of Tyr4. In addition, and the N-terminal amino acid, which is usually Asp1 in tetrapods and Asn1 in fishes, was highly variable (Asp, Asn or Tyr) in chondrichthyans. Molecular phylogenetic analysis showed that chondrichthyan AGT precursors are clustered into a group separated from those of tetrapods and teleosts. The AGT gene was most abundantly expressed in the liver, followed by the kidney, interrenal tissue and rectal gland of Triakis where biological actions of ANG II have been demonstrated. Collectively, we identified diversified AGT genes for the first time in chondrichthyes and showed that their ANG II’s have unique amino acid residues at positions 1, 3 and 4. High variability of ANG II sequences in chondrichthyans is discussed in relation to their unique regulatory mechanisms such as urea-based osmoregulation. [Copyright &y& Elsevier]

This study investigated vasodilator mechanisms in the dorsal aorta of the elephant fish, Callorhinchus milii, using anatomical and physiological approaches. Nitric oxide synthase could only be located in the perivascular nerve fibres and not the endothelium of the dorsal aorta, using NADPH histochemistry and immunohistochemistry. In vitro organ bath experiments demonstrated that a NO/soluble guanylyl cyclase (GC) system appeared to be absent in the vascular smooth muscle, since the NO donors SNP (10−4 mol l−1) and SIN-1 (10−5 mol l−1) were without effect. Nicotine (3 × 10−4 mol l−1) mediated a vasodilation that was not affected by ODQ (10−5 mol l−1), l-NNA (10−4 mol l−1), indomethacin (10−5 mol l−1), or removal of the endothelium. In contrast, the voltage-gated sodium channel inhibitor, tetrodotoxin (10−5 mol l−1), significantly decreased the dilation induced by nicotine, suggesting that it contained a neural component. Pre-incubation of the dorsal aorta with the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP8–37 (10−6 mol l−1) also caused a significant decrease in the nicotine-induced dilation. We propose that nicotine is mediating a neurally-derived vasodilation in the dorsal aorta that is independent of NO, prostaglandins and the endothelium, and partly mediated by CGRP. [ABSTRACT FROM AUTHOR]

Gnathiid larvae (Crustacea; Isopoda; Gnathiidae) infesting elasmobranch and holocephalan fishes from mainly bathyal depths off Suruga Bay, off Kume-jima Island, and five sites from off Tokyo Bay to Shimoda City, Japan were examined. A total of 1460 gnathiid larvae were sampled from 87 host individuals belonging to seven families and 10 species. The morphology of these larvae was distinguishable from other gnathiid species by the head appendages. These larvae presented two pigmentation patterns, stripes or spots, on their dorsal thoraxes in live specimens. Furthermore, they were determined as the second and third stage praniza larvae on the basis of allometric variance of maximum head and abdomen widths. A third stage praniza with stripe pigmentation metamorphosed into an adult male and could be identified as a new species of the genus Thaumastognathia Monod, 1926. The duration between detachment from the host and metamorphosis into male adult required 204 days. This paper describes Thaumastognathia bicorniger sp. nov. on the basis of P3/stripe larvae and the male adult. This report is the first record of the larva and host information for a species of Thaumastognathia .

Abstract: Receptor neurons in the olfactory and vomeronasal epithelia of vertebrates have dendritic specialization that is correlated to the receptor gene family they express and the G protein coupled with that receptor (in particular the G protein alpha subunit). There are not very many data in the literature about the morphological and molecular features of the olfactory epithelium of Chondrichthyes. In this work, the presence and distribution of different types of G protein alpha subunits (Gαo, Gαq and Gαolf) were investigated in the olfactory epithelium of the holocephalan Chimaera monstrosa using immunohistochemistry. Only Gαo-like immunoreactivity was detected in the microvillous receptor neurons and in numerous axon bundles of the fila olfactoria. These preliminary data are in agreement with studies showing G protein alpha subunits in elasmobranchs and support the data present in the literature about putative odorant receptor families in the sequenced genome of the holocephalan Callorhinchus milii. [Copyright &y& Elsevier]

Elasmobranch diets consist of high quantities of protein and lipids, but very low levels of carbohydrates including glucose. Reflecting this diet, most tissues use lipids and ketone bodies as their main metabolic fuel. However, the rectal gland has been shown to be dependent on glucose as a fuel, so we hypothesized that glucose transporters (GLUTs) would be present and upregulated in the gland during times of activation (e.g. following a meal). In this study, we searched for and identified putative class I GLUTs in three elasmobranchs and a holocephalan using transcriptomes, and used these to reconstruct a Bayesian phylogeny. We determined that each of the four species possessed three of the four class I GLUT sequences, but the identities of the isoforms present in each species differed between the elasmobranchs (GLUT1, 3 and 4) and the holocephalan (GLUT1, 2 and 3). We then used qPCR to measure mRNA levels of these GLUTs in the rectal gland, liver, intestine, and muscle of fed and starved spiny dogfish (Squalus suckleyi). The rectal gland data showed higher mRNA levels of GLUT4 in the starved relative to the fed fish. In the muscle, both GLUT1 and 4 were significantly elevated at 24 h post-feeding, as was the case for GLUT4 in the liver. In the intestine on the other hand, GLUT4 was significantly elevated by 6 h post-feeding, remaining elevated through 48 h. We suggest that GLUT4 has taken on the role of GLUT2 in elasmobranchs as the expression patterns observed in the liver and intestine are representative of GLUT2 in other vertebrates., (© 2016. Published by The Company of Biologists Ltd.)