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The American Elasmobranch Society


Abstracts of AES Scientific Papers
American Elasmobranch Society 1997 Annual Meeting
Seattle, Washington
ABSTRACTS - Part 5: Takada through Yano
Takada Koji, Hiruda Hisoka, Wakisaka Seiichiro, Kudo Satoki, Yano Kazunari

 A summary of the freezing, thawing, preservation, and display methodology on a large Megamouth shark, Megachasma petagios

Freezing, thawing, preservation, and display methodology of a large megamouth shark, Megachasma palagios, are summarized. The specimen was frozen (-30 C) from the evening of 29 November 1994 to 1 February 1995. Thawing required nine days, from 1 to 9 February 1995. Half-strength sea-water, with its temperature was held at 3 C by circulating water, was used during the thawing process. After dissection on 9 February 1995, the abdominal cavity was stuffed with blankets and stitched closed to restore the shark's original profile. The specimen was fixed for 45 days in a tank that contained formalin at a concentration of 20%. The size of the acrylic display tank is 500cm X 150 cm X 135 cm. The liquid preservative within the acrylic display tank darkened slightly after about three months.

Trant, John M.

 Molecular aspects of elasmobranch steroid synthesis.

Steroid hormones control a number of physiological processes including osmotic regulation, metabolism, growth, immunity and reproduction. The adrenal and gonadal steroids produced by elasmobranchs were identified many years ago. However, the processes that control steroidogenesis only recently have been examined at the molecular level. The cDNAs encoding steroidogenic enzymes (cytochrome P450 17-hydoxylase, cholesterol side chain cleavage, and 3 beta-hydroxysteroid dehydrogenase [HSD]) have been isolated from two sharks and a stingray Squalus acanthias, Carcharhinus libatus, and Dasyatis americanus). The 17-hydroxylase from the testis of the spiny dogfish shark has been functionally expressed yeast. The enzymology characteristics of cytochrome P450 21-hydroxylase and 3 beta-HSD have been described in the adrenal of the blacktip shark, C. limbatus. The hormonal control of tereoidogenesis in the adrenal of D. sabina has also been examined. Our studies have demonstrated that steroidogenic enzymes isolated from elasmobranch adrenal or gonadal tissue share a relatively high degree of sequence homology and functional characteristics with other vertebrates in spite of their evolutionary distance.

Trivett, Melanie K., Officer, R. A., Clement, J. G., Walker, T. I., Joss, J. M., Ingleton, P. M., Martin, T. J., Danks, J. A.

 Localization of parathyroid hormone-related protein (PTHrP) in bony and cartilaginous fish.

PTHrP is an onco-fetal hormone in mammals and acts on bone and kidney to elevate plasma calcium levels. Normal human kidney and skin contain PTHrP, indicating it probably has paracrine roles. Antibodies to human PTHrP were used to detect PTHrP in circulation and tissues in sea bream Sparrus aurata (Danks et al., 1993) and in dogfish Scyliorhinus canicula (Ingleton et al., 1995). These studies suggest that PTHrP might be a "classical" hormone in fish. In the present study tissues from a range of fish were examined for PTHrP distribution to elucidate possible roles in this group of animals. Samples from marine elasmobranchs through to freshwater bony fish were investigated using antibodies to human PTHrP in immunohistochemistry and a riboprobe to a conserved region of the mammalian gene for in situ hybridization. In all fish examined PTHrP protein and mRNA were found in skin and kidney, similar to higher vertebrates. In elasmobranchs, PTHrP was localized to rectal gland, gills, vertebrae and brain. A similar pattern was observed in rainbow trout. The results indicated that the PTHrP is widespread in lower vertebrates and that there is homology between the PTHrP molecules found in man and fish.

Van Dykhuizen, Gilbert, Light, Karen, Wrobel, David, Powell, David

 Ratfish romance at the Monterey Bay Aquarium

Mating observations of the Pacific ratfish, Hydrolagus collieri, were recorded on two separate occasions. The positioning of the male ratfish in relation to the female ratfish and the use of the cephalic and pelvic claspers were videotaped and photographed. Records indicate egg capsules are deposited throughout the year but viability of egg capsules appears to vary.

Villavicencio-Garayzar, C.J.

 Reproductive biology of the horn shark, Heterodontus francisci, in Mexican waters.

The horn shark, Heterodontus francisci is an abundant species in the Pacific coast of Baja California Peninsula, which have no commercial value. A study on its biology was carried out at the San Ignacio Lagoon between August 1992 and June 1994. The sharks were caught with gill nets. The months with the largest abundances were April to June, in this period males dominated the sex ratio near 2:1. From August to February, only immature organisms were caught, but in late spring and early summer, mature were more abundant. The maximum size found in both males and females were 78 cm TL. In males the maturiy began at 50 cm TL, and is reached at 55-60 cm; in April and May, all males carried semen. Based on oocyte diameter, nidamental gland and egg case in uterus, the maturity size for females is at 63 cm TL. The maximum number of oocytes seen in females were 10 to 12. In conclusion, tile horn shark is an oviparous species that enters San Ignacio Lagoon in April, for mating and egg case formation, and stays until June or July, when males and females migrate out. Details on its embryonic development remain still largely unknown.

Visconti, M.A., Castrucci, A.M.L.

 Regulation of elasmobranch color change.

An evaluation of the current state-of-the-art of pigment cell receptors and mechanisms of cell signaling in the elasmobranch fish will be presented. The studies regarding regulaton of pigment cell function in elasmobranchs are very scarce. So far, the following aspects have been investigated: 1) a variety of neural and hormonal agents (MCH, catecholamines and melatonin) failed to induce pigment granule translocations; 2) Both acetylated and desacetylated forms of alpha-MSH seem to be secreted by pars intermedia, but the former not only prevails, but is also more potent in in vitro and in vivo skin bioassays, suggesting that it is the physiological factor regulating elasmobranch color changes; 3) Immunoreactivity to MSH and MCH has been found in various hypothalmic regions and thalamic and mesencephalic fibers of 3 species, suggesting that they may also play a role as central neuromodulators or neurotransmitters; 4) the U light is an important mitogenic and melanogenic agent for mammalian melanocytes, and its physiological role has also been determined in the juveniles of the elasmobranch Sphyrna lewini, which shows an increase in the skin melanin content in response to increase in solar radiation.

Volkoff, H., Wourmes, J.P., Amesbury, E.L., Snelson, F.F.

 Thyroid function and reproductive cycle in the Atlantic stingray, Dasyatis sabina.

This study carried out to examine the role of the thyroid gland in the control of reproduction in the viviparous Atlantic stingray, Dasyatis sabina. Thyroid activity of individuals in different reproductive states was assessed both by histological and ultrastructural examination of the gland, and by analysis of circulating levels of thyroid hormones. Stingray follicular cells possess characteristic features such as a single apical cilium, and a well-developed endoplasmic reticulum. They vary in size and shape, according to the activity of the gland. The average levels of serum thyroid hormones are 1.6 µg/100ml for total thyroxine (T4), and 2 ng/ml for total triiodothyronine (T3). Immature individuals have resting glands and low levels of circulating thyroid hormones. Females undergoing oogenesis have low serum hormone levels and moderately active glands. High thyroid gland activity, and high levels of circulating thyroid hormones is seen in females, from ovulation until mid-gestation. Hormonal levels and gland activity decline during the second half of gestation and in post-partum females. The decline in activity of the maternal gland may correspond to the beginning of autonomous function of the fetal thyroid gland, i.e. the time at which the maternal supply of thyroid hormones is no longer needed by the embryo.

Walsh, Cathy J., Luer, Carl A.

 Preliminary investigation of cell proliferation and programmed cell death in elasmobranch thymus.

Elasmobranchs represent the earliest phylogenetic appearance of a clearly defined thymus. Cell proliferation and programmed cell death, or apoptosis, are critical steps in shaping the immune repertoire in higher vertebrate thymi. Using the DNA analog, bromodeoxyuridine, cells undergoing DNA synthesis were found throughout the thymus of two species of elasmobranch fish, the clearnose skate (Raja eglanteria ) and the nurse shark (Ginglymostoma cirratum). The majority of proliferative activity was found in thymic cortex, as it is in higher vertebrates. Similarly, using a method to detect DNA strand breaks, apoptosis was observed throughout the thymus, but appeared to be more prevalent in the thymic cortex. Additionally, both proliferating and apoptotic cells were found associated with cells which appear to be phylogenetic counterparts of specialized cells called thymic nurse cells (TNC) recently described in higher vertebrate thymi. TNC may be involved with removal of apoptotic cells from the thymus, as well as with proliferation and maturation of thymocytes. Understanding the function and significance of the thymus and TNC in a phylogenetically primitive vertebrate contributes to understanding the evolution of lymphocytes and lymphocyte maturation processes in higher vertebrate immune systems. Supported in part by a grant to CJW by the National Science Foundation (MCB95-09105).

Wetherbee, Bradley, M.

 Lipid Composition of deep-sea sharks from the Chatham Rise, New Zealand

Deep-sea sharks approach neutral buoyancy by means of a large, oily liver that contains large amounts of low-density lipids, primarily squalene and diacyl glycerol ether (DAGE). As an animal increases in size and matures sexually, many biochemical changes take place within that animal. It was hypothesized that maintenance of neutral buoyancy in deep-sea sharks involves fine-scale adjustments in the chemical composition of liver oil as individuals grow and develop. To test this hypothesis the lipid composition of liver oil of individuals of different sizes and sex for several species of deep-sea sharks collected from the Chatham Rise, New Zealand were compared. The composition of liver oil varied within, and among species. Several species contained large amounts of squalene and DAGE, whereas only traces of these lipids were present in other species. There was an inverse relationship between the amount of squalene and DAGE in liver oil, and squalene content tended to decrease as sharks increased in size. The species with liver lipid characteristics most desirable for commercial exploitation were not abundant on the Chatham Rise. Maintenance of neutral buoyancy in deep-sea sharks is a dynamic process that involves changes in the composition of low-delisity liver lipids as the sharks increase in size.

Wilga, Cheryl D.

 Feeding Mechanics in the Bonnethead Shark, Sphyrna tiburo.

This kinematics and motor activity during feeding in the bonnethead shark Sphyrna tiburo is quantified using anatomy, video and electromyography. Sphyrna tiburo exhibits tropotactic behavior while searching for potential prey. Prey capture is by ram feeding, supported by a ram-suction index of 0.38, in which the mouth is opened wide and the prey is grasped by the lower jaw. Hypotheses relating cranial movements to muscle activity are supported: the coracomandibuaris muscle is active concomitant with lower jaw depression; the epaxialis muscle is active concurrent with cranial elevation; the quadratomandibularis dorsal muscle is active concurrent with lower jaw elevation; the preorbitalis ventral and levator palatoquqadrati muscles are active concombitant with upper jaw protrusion; and the levantor hyomandibularis muscle is active concurrent with jaw retraction. The basic feeding mechanism in S. tiburo is conserved in diverse shark taxa. A relative slowing of movements with increasing body size occurred in some jaw movements, but the relative pattern remained the same. Molariform teeth in S. tiburo may be an adaptation for crushing hard shelled prey. Transport of the prey from the jaw to the esophagus is by suction. The basic feeding sequence in conserved in sharks, rays, bony fishes, aquatic salamanders, and aquatic turtles.

Wyffels, Jennifer T., Bodine, A. B., Luer, Carl A., Walsh, Cathy J.

 Development of the lymphomyeloid system in the Clearnose skate, Raja eglanteria.

Clearnose skate embryos were fixed in 10% formalin in elasmobranch-ringers at regular intervals during their 12 week developmental period. Preserved skates were processed by routine histological methods, embedded in either paraffin wax or methacrylate resin, sectioned at 2-6 microns, and stained with hematoxylin and eosin. Organogenesis was examined for the major components of the immune system, viz., spleen, thymus, leydig, and epigonal. The skate thymus is bilaterally paired, dorsomedial to the gills. Each lobe is comprised of 4 primordia formed from epithelia] evaginations from each of the bronchial pouches 2-5. The thymus is the first lymphoid organ to appear and is nearly contiguous at 4 weeks. Cortical and medullary zones as well as lobuies are pronounced after 6 weeks. The spleen is present as a swelling in the dorsal mesogastrium adjacent to the stomach by week 4. The spleen continues to enlarge with little or no distinction between red and white pulp until after hatching. The leydig is found in the dorsal and ventral submucosa of the esophagus by week 6. The epigonal is the last immune organ to develop. Granulocytes appear within the genital ridge by week 8.

Yano, Kazunari, Mori, Hideki, Minamikawa, Kiyoshi, Ueno, Shoogo, Toda, Minoru, Uchida, Senzo

 Behavioral response of sharks to electric stimulation

The behavioral responses of four species of sharks, Carcharhinus falcifortnis (60 cm TL), Triaenodon obesus (119 cm TL), Galeocerdo cuvier (218 cm TL), and Stegostoma fasciatum (220 cm TL), to electric stimulation were studied. The captive sharks swam in a tank (7 m in diameter). The source unit consisted of a signal generator and a power amplifier. The signal generator produced the wave form, frequency, and voltage. Electrodes were 5-cm x 10-cm copper plates, separated by a distance of 3.5 m. A 60-Hz sine wave and DC pulse electric fields were chosen. The 60-Hz sine wave was 10 V (r.m.s) and the DC pulse period was either 1 sec or 5 sec (duty ratio is 10%). All sharks swam close to the sides of the tank when the signal generator was off. When the 60-Hz sine wave and DC pulse electric fields were being produced, two species, C. falciformis and T. obesus, immediately turned round. Many turns of the sharks were associated with the DC pulse electric fields. Conversely, G. cuvier and S. fasciatum did not change thier swimming patterns when the signal generator was on. Hence, the behavioral response patterns were different among the species.