Figure 3 - available via license: Creative Commons Attribution 4.0 International
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Length (±standard deviation) of the external gill filaments on the first gill slit for 35 embryos. The above figures represent the ventral view of the head and pharyngeal region. 1st eg = external gill filaments on the first gill slit.
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Respiration in fishes involves buccal pumping, which is characterized by the generation of nearly continuous water flow over the gills because of the rhythmic expansion/compression of the pharyngeal cavity. This mechanism is achieved by the functions of the vascular, skeletal, and muscular systems. However, the process by which the embryo establish...
Citations
... In catshark, the external gills appear at stage 27 and reach a maximum length at stage 32 (Takagi et al. 2017). Thereafter, the external gills regressed and disappeared by stage 34, whereas the gill lamellae developed and remained inside the gill slit (Takagi et al. 2017;Tomita et al. 2014). ...
... In catshark embryos, the external gills reached the maximum length at stage 32, while pre-hatching occurs during stage 31 (Takagi et al. 2017). After pre-hatching, the embryo starts buccal pumping for respiration to pass water over the developed internal gills (Tomita et al. 2014). These findings indicate that the primary site of respiration in catshark embryo shifted from the external gills to the internal gills located inside the gill slit after pre-hatching. ...
... These findings indicate that the primary site of respiration in catshark embryo shifted from the external gills to the internal gills located inside the gill slit after pre-hatching. The respiratory function of external and internal gills has been mentioned in some studies (Hamlett et al. 1985;Pelster and Bemis 1992;Leonard et al. 1999;Tomita et al. 2014); however, to our knowledge, the The gill filaments inside the gill slits were already recognizable at stage 30, but ionocyte was not yet detected. At stage 31, by means of immunohistochemistry with the antisera specific for NKA and V-ATPase, both type-A and type-B ionocytes appeared on the gill filaments (Fig. 2a). ...
In teleost fish, branchial ionocytes are important sites for osmoregulation and acid-base regulation by maintaining ionic balance in the body fluid. During the early developmental stages before the formation of the gills, teleost ionocytes are localized in the yolk-sac membrane and body skin. By comparing with teleost fish, much less is known about ionocytes in developing embryos of elasmobranch fish. The present study investigated the development of ionocytes in the embryo and larva of cloudy catshark, Scyliorhinus torazame. We first observed ionocyte distribution by immunohistochemical staining with anti-Na⁺/K⁺-ATPase (NKA) and anti-vacuolar-type H⁺-ATPase (V-ATPase) antibodies. The NKA- and V-ATPase-rich ionocytes appeared as single cells in the gill filaments from stage 31, the stage of pre-hatching, while the ionocytes on the body skin and yolk-sac membrane were also observed. From stage 32, in addition to single ionocytes on the gill filaments, some outstanding follicular structures of NKA-immunoreactive cells were developed to fill the inter-filament region of the gill septa. The follicular ionocytes possess NKA in the basolateral membrane and Na⁺/H⁺ exchanger 3 in the apical membrane, indicating that they are involved in acid-base regulation like single NKA-rich ionocytes. Three-dimensional analysis and whole-mount immunohistochemistry revealed that the distribution of follicular ionocytes was limited to the rostral side of gill septum. The rostral sides of gill septum might be exposed to faster water flow than caudal side because the gills of sharks gently curved backward. This dissymmetric distribution of follicular ionocytes is considered to facilitate efficient body-fluid homeostasis of catshark embryo.
... The immune system is considered to be functional before the pre-hatching event, as immunoglobulin-positive cells are detected in most of the lymphomyeloid system (liver, interrenal, thymus, spleen and Leydig organ) in the lesser spotted dogfish embryo (Lloyd-Evans, 1993). In relation to respiratory function, the cloudy catshark and port Jackson shark (Heterodontus portusjacksoni) embryos begin buccal pumping, just after the prehatching event (Rodda and Seymour, 2008;Tomita et al., 2014). ...
Cartilaginous fish have a comparatively short intestine known as the spiral intestine that is comprised of a helical spiral of intestinal mucosa. However, morphological and functional development of the spiral intestine is not well described. Unlike teleosts, cartilaginous fish are characterized by an extremely long developmental period in ovo or in utero for example; in the oviparous cloudy catshark (Schyliorhinus torazame), the developing fish remains inside the egg capsule for up to six months, suggesting that the embryonic intestine may become functional prior to hatch. In the present study, we describe the morphological and functional development of the spiral intestine in the developing catshark embryo. Spiral formation of embryonic intestine was completed at the middle of stage 31, prior to "pre-hatching", which is a developmental event characterized by the opening of egg case occurring at the end of the first third of development. Within 48 hours after pre-hatching event, egg yolk began to flow from the external yolk sac into the embryonic intestine via the yolk stalk. At the same time, there was a rapid increase in mRNA expression of the peptide transporter pept1 and neutral amino acid transporter slc6a19 Secondary folds in the intestinal mucosa and microvilli on the apical membrane appeared after pre-hatching, further supporting the onset of nutrient absorption in the developing intestine at this time. We demonstrate the acquisition of intestinal nutrient absorption at the pre-hatching stage of an oviparous elasmobranch.
... The results of this study reveal that buccal pumping is a good indicator for distinguishing between the early and middle developmental stages of the reef manta ray. This observation is similar to the observations of the oviparous catshark species, the small-spotted catshark (Scyliorhinus canicula), and the cloudy catshark (Scyliorhinus torazame), in which embryos first exhibited buccal pumping during the middle gestation period, after the jaw and hyoid structure are fully developed (Diez and Davenport, 1987;Thomason et al., 1996;Tomita et al., 2014). Interestingly, in this study, we failed to observe any evidence of tail-waving movement, which is typically observed in oviparous batoids (Diez and Davenport, 1987;Thomason et al., 1996). ...
... Documentation of buccal pumping in the manta ray embryo may also have evolutionary implications in the transition from oviparous (egg laying) to viviparous reproductive modes. Buccal pumping has also been reported in late-stage embryos of several oviparous elasmobranchs, such as Chiloscyllium plagiosum, Heterodontus portusjacksoni, Scyliorhinus canicula, and Scyliorhinus torazame (Diez and Davenport, 1987;Tullis and Peterson, 2000;Rodda and Seymour, 2008;Tomita et al., 2014). This implies that viviparous and oviparous elasmobranchs develop embryonic respiratory mechanisms through similar processes. ...
... Most viviparous elasmobranch species lack an embryo-maternal connection, thus the embryo must acquire oxygen from the surrounding uterine fluid (Tomita et al., 2012). Oxygen uptake during early gestation of catshark and bullhead shark embryos is carried out via passive diffusion into external gill filaments, later shifting to buccal pumping to facilitate ventilation of the branchial arches, at which point the external gill filaments are resorbed (Rodda and Seymour, 2008;Tomita et al., 2014). Dogfishes (Squalus spp.) likely follow a similar pattern as external gill filaments have been observed in early to mid-gestation for S. acanthias (Scammon, 1911) and in all three species of the present study (Cotton and Tomita, unpublished data). ...
... In summary, we hypothesize that respiration in late-stage dogfish embryos relies primarily on gill ventilation using periodically replenished uterine seawater, similar to the oviparous reproductive mode. Embryos of oviparous elasmobranchs obtain oxygen from seawater introduced from the external environment through respiratory slits in the egg capsule (Diez and Davenport, 1987;Tullis and Peterson, 2000;Rodda and Seymour, 2008;Tomita et al., 2014). The oxygen demand of a developing embryo increases exponentially with body size (Diez and Davenport, 1987;Tullis and Peterson, 2000), hence, dissolved oxygen supplied from the uterine wall may suffice during early and mid-stage embryonic respiration but our results show that it is likely insufficient to support late-stage embryos. ...
Cartilaginous fishes have various unique physiological features such as cartilaginous skeletons and a urea‐based osmoregulation strategy for adaptation to their marine environment. Also, because they are a sister group of bony vertebrates, understanding their unique features is important from an evolutionary perspective. However, genetic engineering, which can analyze gene functions as well as cellular behavior, has not been effectively utilized in cartilaginous fishes. This is partly because their reproductive strategy involves internal fertilization, which results in difficulty in microinjection into fertilized eggs at the early developmental stage. Here, to identify efficient gene transfer methods in cartilaginous fishes, we examined the effects of various methods both in vitro and in vivo using the cloudy catshark, a candidate model cartilaginous fish species. In all methods, green fluorescent protein (GFP) expression was used to evaluate exogenous gene transfer. First, we examined gene transfer to primary cultured cells from cloudy catshark embryos by lipofection, polyethylenimine (PEI), adenovirus, baculovirus and electroporation. Among the methods tested, lipofection, electroporation and baculovirus infection enabled the successful transfer of exogenous genes into primary cultured cells. We then attempted in vivo transfection into cloudy catshark embryos by electroporation and baculovirus infection. Although baculovirus‐injected groups did not show GFP fluorescence, electroporation successfully introduced GFP into muscle cells. Furthermore, we succeeded in GFP transfer into adult tissues by electroporation. The in vitro and in vivo gene transfer methods that worked in this study may identify paths for future genetic manipulation including knockout experiments and cellular linage analysis in cartilaginous fishes.
Significance
We sequenced and analyzed the genome of the endangered whale shark, the largest fish on Earth, and compared it to the genomes of 84 other species ranging from yeast to humans. We found strong scaling relationships between genomic and physiological features. We posit that these scaling relationships, some of which were remarkably general, mold the genome to integrate metabolic constraints pertaining to body size and ecological variables such as temperature and depth. Unexpectedly, we also found that the size of neural genes is strongly correlated with lifespan in most animals. In the whale shark, large gene size and large neural gene size strongly correlate with lifespan and body mass, suggesting longer gene lengths are linked to longer lifespans.
