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Due to their important phylogenetic position among extant vertebrates, sharks are an invaluable group in evolutionary developmental biology studies. A thorough understanding of shark anatomy is essential to facilitate these studies and documentation of this iconic taxon. With the increasing availability of cross-sectional imaging techniques, the complicated anatomy of both cartilaginous and soft tissues can be analyzed non-invasively, quickly, and accurately. The aim of this study is to provide a detailed anatomical description of the normal banded houndshark (Triakis scyllium) using computed tomography (CT) and magnetic resonance imaging (MRI) along with cryosection images. Three banded houndsharks were scanned using a 64-detector row spiral CT scanner and a 3 T MRI scanner. All images were digitally stored and assessed using open-source Digital Imaging and Communications in Medicine viewer software in the transverse, sagittal, and dorsal dimensions. The banded houndshark cadavers were then cryosectioned at approximately 1-cm intervals. Corresponding transverse cryosection images were chosen to identify the best anatomical correlations for transverse CT and MRI images. The resulting images provided excellent detail of the major anatomical structures of the banded houndshark. The illustrations in the present study could be considered as a useful reference for interpretation of normal and pathological imaging studies of sharks.

An endocrine glucocorticoid response following exposure to a stressor has been well described for many vertebrates. However, despite demonstration of secondary stress responses in a number of elasmobranchs, our understanding of the endocrine control of these responses is lacking. This is largely due to the unusual structure of the dominant corticosteroid in elasmobranch fish, 1α-hydroxycorticosterone (1α-OH-B). Here we describe plasma extraction and HPLC separation procedures that allowed for the measurement of 1α-OH-B and corticosterone from plasma samples in the cannulated, conscious free-swimming Japanese banded houndshark, Triakis scyllium. While patterns of concentration in the plasma for 1α-OH-B and corticosterone were found to be similar in all experiments conducted, circulating levels of 1α-OH-B were consistently 100-fold greater than circulating levels of corticosterone. Immediately following cannulation surgery, circulating levels of 1α-OH-B increased 7-fold compared to pre-surgery levels, while the levels were 11-fold higher than pre-stress levels 30 min post a repeated handling/air-exposure stress. A three week period of fasting resulted in a 22-fold increase in circulating levels of 1α-OH-B in the banded houndshark. This is the first report of direct measurement of changes in circulating levels of the primary corticosteroid in elasmobranch fish, 1α-OH-B, following exposure to a stressor such as handling/air-exposure. Data indicate the steroid may respond similarly to the classic glucocorticoid response, such as cortisol in teleosts.

Most of the cartilaginous fishes live principally in seawater (SW) environments, while a limited number of species including the bull shark, Carcharhinus leucas, inhabit both SW and freshwater (FW) environments during their life cycle. Euryhaline elasmobranchs maintain high internal urea and ion levels even in FW environments, but little is known about the osmoregulatory mechanisms that enable them to maintain internal homeostasis in hypoosmotic environments. In the present study, we focused on the kidney because this is the only organ that can excrete excess water from the body in a hypoosmotic environment. We conducted a transfer experiment of bull sharks from SW to FW and performed differential gene expression analysis between the two conditions using RNA-seq. A search for genes up-regulated in the FW-acclimated bull shark kidney indicated that the expression of the Na+-Cl− cotransporter (NCC; Slc12a3) was ten times higher in the FW-acclimated fish compared to that in SW fish. In the kidney, apically-located NCC was observed in the late distal tubule and in the anterior half of collecting tubule where basolateral Na+/K+-ATPase was also expressed, implying that these segments contribute to NaCl reabsorption from the filtrate for diluting the urine. This expression pattern was not observed in the houndshark, Triakis scyllium, that had been transferred to 30% SW; this species cannot survive in FW environment. The salinity transfer experiment combined with a comprehensive gene screening approach demonstrates that NCC is a key renal protein that contributes to the remarkable euryhaline ability of the bull shark.

Batoidea (rays and skates) is a monophyletic subgroup of elasmobranchs that diverged from the common ancestor with Selachii (sharks) about 270 Mya. A larger number of batoids can adapt to low-salinity environments, in contrast to sharks, which are mostly stenohaline marine species. Among osmoregulatory organs of elasmobranchs, the kidney is known to be dedicated to urea retention in ureosmotic cartilaginous fishes. However, we know little regarding urea reabsorbing mechanisms in the kidney of batoids. Here, we performed physiological and histological investigations on the nephrons in the red stingray (Hemitrygon akajei) and two shark species. We found that the urine/plasma ratios of salt and urea concentrations in the stingray are significantly lower than those in cloudy catshark (Scyliorhinus torazame) under natural seawater, indicating that the kidney of stingray more strongly reabsorbs these osmolytes. By comparing the three-dimensional images of nephrons between stingray and banded houndshark (Triakis scyllium), we showed that the tubular bundle of stingray has a more compact configuration. In the compact tubular bundle of stingray kidney, the distal diluting tubule was highly developed and frequently coiled around the proximal and collecting tubules. Furthermore, co-expression of NKAα1 (Na+/K +-ATPase) and NKCC2 (Na+- K+-2Cl– cotransporter 2) mRNAs was prominent in the coiled diluting segment. These findings imply that NaCl reabsorption is greatly facilitated in the stingray kidney, resulting in a higher reabsorption rate of urea. Lowering the loss of osmolytes in the glomerular filtrate is likely favorable to the adaptability of batoids to a wide range of environmental salinity.

Animal cells have been widely and continuously studied due to their usefulness in biological researches and production of pharmacological agents as well as food additives. Nevertheless, there are several problems such as the existence of viruses which introduce the possibility of mammalian-infection. In this reason, recently, animal cells derived from marine organisms have emerged to overcome these problems by many researches. However, marine animal-derived cells have not yet been well developed. The banded hound shark occupies an important position in an evolutionary perspective and currently a few biological substances have been used for medicines or food additives such as shark squalene and cartilage extract. In this study, primary cells were cultivated from a banded hound shark nose containing many extracellular matrix (ECM) materials. After successful isolation of one type of primary nasal cell, we optimized culture conditions including coating materials, media composition, serum concentrations and pH. Additionally, these cells demonstrated proliferation ability in vitro, generating secretions of collagen and sulfated polysaccharides. The cultivated primary cells are useful in the study of cellular biology and may be used to create a variety of ECM-originated bioactive substances.

In teleost fishes, it is well-established that the gill serves as an important ionoregulatory organ in addition to its primary function of respiratory gas exchange. In elasmobranchs, however, the ionoregulatory function of the gills is still incompletely understood. Although two types of ionocytes, Na(+)/K(+)-ATPase (NKA)-rich (type-A) cell and vacuolar-type H(+)-ATPase (V-ATPase)-rich (type-B) cell, have been found in elasmobranch fishes, these cells were considered to function primarily in acid-base regulation. In the present study, we examined ion-transporting proteins expressed in ionocytes of Japanese-banded houndshark, Triakis scyllium, reared in full-strength seawater (SW) and transferred to diluted (30%) SW. In addition to the upregulation of NKA and Na(+)/H(+) exchanger type 3 (NHE3) mRNAs in the type-A ionocytes, we found that Na(+), Cl(-) cotransporter (NCC, Slc12a3) is expressed in a subpopulation of the type-B ionocytes, and that the expression level of NCC mRNA was enhanced in houndsharks transferred to a low-salinity environment. These results suggest that elasmobranch gill ionocytes contribute to NaCl uptake in addition to the already described function of acid-base regulation, and that NCC is most probably one of the key molecules for hyper-osmoregulatory function of elasmobranch gills. The existence of two types of ionocytes (NHE3- and NCC-expressing cells) that are responsible for NaCl absorption seems to be a common feature in both teleosts and elasmobranchs for adaptation to a low salinity environment. A possible driving mechanism for NCC in type-B ionocytes is discussed.

In teleost fishes, it is well-established that the gill serves as an important ionoregulatory organ in addition to its primary function of respiratory gas exchange. In elasmobranch fish, however, the ionoregulatory function of the gills is still poorly understood. Although mitochondria-rich (MR) cells have also been found in elasmobranch fish, these cells are considered to function primarily in acid-base regulation. In this study, we found a novel aggregate structure made up of cells with basolaterally-expressed Na(+)/K(+)-ATPase (NKA), in addition to NKA-immunoreactive MR cells that have already been described in the gill filament and lamella. The cell aggregates, named follicularly-arranged NKA-rich cells (follicular NRCs), were found exclusively in the epithelial lining of the venous web in the cavernous region of the filament and the inter-filamental space of the gill septum. The follicular NRCs form a single-layered follicular structure with a large lumen leading to the external environment. The follicular NRCs were characterized by: (i) well-developed microvilli on the apical membrane, (ii) less prominent infoldings of the basolateral membrane and (iii) typical junction structures including deep tight junction between cells. In addition, large numbers of vesicles were observed in the cytoplasm and some of them were fused to the lateral membrane. The follicular NRCs expressed Na(+)/H(+) exchanger 3 and Ca(2+) transporter 1. The follicular NRCs thus have the characteristics of absorptive ionoregulatory cells and this suggests that the elasmobranch gill probably contributes more importantly to body fluid homeostasis than previously thought.

A new species of the genus Hemitriakis Herre, 1923 (Family Triakidae, Order Carcharhiniformes), is described from off the islands of Bali and Lombok in eastern Indonesia. Hemitriakis indroyonoi is separable from the other congeners, H. abdita, H. complicofasciata, H. falcata, H. japanica and H. leucoperiptera, by a combination of vertebral counts, morphometric characters, and juvenile coloration. H. indroyonoi is most similar to H. falcata from northwestern Australia but differs in juvenile coloration, some meristic and morphological characters, size and cranial morphology. The new species is allopatric to other members of this genus.

A new species of Coronocestus Caira, Marques, Jensen, Kuchta and Ivanov, 2013 is described from Iago omanensis (Norman) from the Gulf of Oman. Coronocestus ehsanentezarii sp. nov. differs from C. musteli (Pintner, 1889) Caira, Marques, Jensen, Kuchta and Ivanov, 2013 in that its ovary is H- rather than U-shape. The new species is easily distinguished from C. diamanti (Ivanov and Lipshitz, 2006) Caira, Marques, Jensen, Kuchta and Ivanov, 2013 by the number of spines per column on the cephalic peduncle (24-36 vs 95-118). It differs from C. hormozganiense (Haseli, Malek, Palm and Ivanov, 2012) Caira, Marques, Jensen, Kuchta and Ivanov, 2013 based on a greater number of spines per column on the cephalic peduncle (24-36 vs 18-21). The new species differs from C. notoguidoi (Ivanov 1997) Caira, Marques, Jensen, Kuchta and Ivanov, 2013 in that of its scolex is craspedote rather than acraspedote. Unlike C. coronatum (Robinson 1959) Caira, Marques, Jensen, Kuchta and Ivanov, 2013, C. ehsanentezarii sp. nov. possesses 29-35 rather than 20 apical hooks in each dorso-ventral group. The new species possesses lateral hooklets with two rows (a and b designations) in each cluster. This character had been presented earlier only for Andocadoncum Abbott and Caira, 2014. Furthermore, a new locality record is presented for C. diamanti from Iago omanensis in the Gulf of Oman. Thus, I. omanensis certainly hosts two diphyllidean species simultaneously in the Gulf of Oman. The generic diagnosis of Coronocestus is also revised to include new data.

Na+/H+exchanger 3 (NHE3) provides one of the major Na+absorptive pathways of the intestine and kidney in mammals, and recent studies of aquatic vertebrates (teleosts and elasmobranchs) have demonstrated that NHE3 is expressed in the gill and plays important roles in ion and acid-base regulation. To understand the role of NHE3 in elasmobranch osmoregulatory organs, we analyzed renal and intestinal expressions and localizations of NHE3 in a marine elasmobranch, Japanese banded houndshark ( Triakis scyllium). mRNA for Triakis NHE3 was most highly expressed in the gill, kidney, spiral intestine, and rectum. The kidney and intestine expressed a transcriptional isoform of NHE3 (NHE3k/i), which has a different amino terminus compared with that of NHE3 isolated from the gill (NHE3g), suggesting that NHE3k/i and NHE3g arise from a single gene by alternative promoter usage. Immunohistochemical analyses of the Triakis kidney demonstrated that NHE3k/i is expressed in the apical membrane of a part of the proximal and late distal tubules in the sinus zone. In the bundle zone of the kidney, NHE3k/i was expressed in the apical membrane of the early distal tubules known as the diluting segment. In the spiral intestine and rectum, NHE3k/i was localized toward the apical membrane of the epithelial cells. The transcriptional levels of NHE3k/i were increased in the kidney when Triakis was acclimated in 130% seawater, whereas those in the spiral intestine were increased in fish acclimated in diluted seawater. These results suggest that NHE3 is involved in renal Na+reabsorption, urine acidification, and intestinal Na+absorption in elasmobranchs.

Public perception has been that an apparent increase in the nearshore occurrence of white sharks Carcharodon carcharias in False Bay, on the south coast of South Africa, can at least be partly attributed to beach-seine (treknet) operations attracting sharks into this coastal area. To assess the merit of these concerns, all available beach-seine catch-and-effort data from the False Bay fishery over a 32-year period were analysed. A total of 27 cartilaginous species from 15 families was recorded in around 11 400 hauls from 1974 to 2006. Most (98%) of these comprised small benthic invertebrate feeders such as smooth houndshark Mustelus mustelus and lesser guitarfish Rhinobatos annulatus. Large sharks such as C. carcharias and ragged-tooth shark Carcharias taurus were rare, occurring in