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The American Elasmobranch Society


Abstracts of AES Scientific Papers
American Elasmobranch Society 1990 Annual Meeting
Charleston, South Carolina
ABSTRACTS - Part 4: Oetinger through Zheng
(Presenting author's name in BOLDFACE
OETINGER, M.I. and T.B. Thorson LATER DEVELOPMENTAL STAGES OF THE SAWFISH, PRISTIS PEROTTETI.

Since to date only one developmental stage of a pristid has been described, the present study was undertaken to chronicle the developmental stages of a collection of 150 specimens from Lake Nicaragua. Thirty-one characters were measured and analyzed to describe growth relationships between structures. Major developmental events unique to pristids included the following: the rostrum, not formed in the smallest specimen, had elongated in a 33 mm fetus and could be distinguished as a developing saw; rostral teeth, the number of which is the main diagnostic character in separating the species of Pristis, were sufficiently developed to be counted in a 158 mm fetus, and pectorals were completely fused to the head by the time fetuses reached 92 mm in length.

PARSONS, G.R. GEOGRAPHIC VARIATION IN REPRODUCTION AMONG POPULATIONS OF THE BONNETHEAD SHARK, SPHYRNA TIBURO.

A study of two populations of the bonnethead shark, Sphyrna tiburo was conducted in the Florida Keys and in Tampa Bay, Florida from September, 1982 to December, 1986. The maintenance of sharks in captivity at the Marine Science and Conservation Center in the Florida Keys, and the collection of sharks from widely separated geographical areas allowed the examination of latitudinal variation in reproduction. Several parameters were found to differ: (1) size and age at maturation (2) mating season (3) rate of embryonic development (4) size at birth (5) the energetic investment in producing offspring (6) gestation period and (7) the incidence of infertility. Litter size was not statistically different between the two populations. It is noteworthy that the average size of adult sharks in Tampa Bay is significantly greater than that of Florida Keys sharks. This size difference may be important in explaining the observed differences in reproductive strategy.

PIERANTONI, R., M. D'Antonio, and S. Fasano MORPHO-FUNCTIONAL ASPECTS OF THE HYPOTHALAMUS-PITUITARY-GONADAL AXIS.

Among vertebrates, the general feature of the tetrapod hypothalamus-pars distalis axis is the presence of a portal system. oN the contrary, in Elasmobranch fishes there is general consensus indicating the absence of a vascular supply from the hypothalamus in the ventral lobe where gonadotropin activity is detectable. The hypothalamus contains GnRH immunoreactivity and GnRH acts increasing plasma gonadal steroids probably via a ventral lobe stimulation. Therefore a question arises: how GnRH reaches the pituitary. Since hydrophobic forms of GnRH have been shown to be present in the few species studies so far, we suggest that the plasma route might be practicable. This may allow the GnRH to reach the gonads and to act also by direct mechanisms. Intragonadal levels of steroids may have a paracrine and/or autocrine role in ovary and testis. Particularly, the morphology of the testis supports the concept of a diverse environment for different spermatogenic stages. Finally, gonadal steroids may feedback pituitary activity.

PIKE, C.S. and S.H. Gruber FLUCTUATIONS IN SERUM CALCIUM LEVELS OF CAPTIVE LEMON SHARKS NEGAPRION BREVIROSTRIS.

Age estimation in elasmobranchs is accomplished by counting calcified rings in vertebral centra without the knowledge and understanding of the importance of serum calcium. Blood from juvenile lemon sharks, Negaprion brevirostris, was collected, caudally via venipuncture, once weekly for a period of 19 weeks. Calcium levels ranged from 12.1 mg/dl to 22 mg/dl. Calcium levels in all sharks reached a peak during the ninth and tenth weeks of the study. This peak was immediately followed by a sudden decline in calcium levels. Autocorrelation showed no relationship of serum calcium to other blood parameters. Presently, deposition of vertebral rings is being correlated with fluctuations in serum calcium and environmental variables.

PRATT, H.L. Jr. STORAGE OF SPERMATOZOA BY LARGE ATLANTIC SHARKS.

Storage of spermatozoa in the oviducal gland is used advantageously by several species of large Atlantic sharks. Using light microscopy I have observed females of: Alopias vulpinus, Lamna nasus, Carcharhinus obscurus, Prionace glauca, Sphyrna lewini, and S. tiburo. Details of sperm retention remain unresolved. Gravid females of the two carcharhinid and two sphyrnid species examined often possess oviducal spermatozoa. This suggests that multiple litters may be fertilized by one insemination. Male sharks also store spermatozoa in the ampulla ducts epididymis as sperm packets; variously termed spermatophores and spermozeugma. These packets disintegrate before reaching the oviducal gland.

PRYOR, W.W. TOWARDS A NATIONAL ELASMOBRANCH INVENTORY.

Leo Demski suggested the development of a national inventory at the 1989 meeting of the American Elasmobranch Society in San Francisco. To that end, I have developed a semiannual regional inventory of live, captive sharks and rays for fourteen institutions (3 public aquariums, 10 zoos, and 1 university). The Great Lakes Region includes the states: MI, OH, KY, IN, IL, WI, MN, IA, and MO. The January 1990 edition of the Great Lakes Inventory showed 89 specimens of 16 shark species, and 62 specimens of 13 ray species. Coordinators are currently working on similar inventories for the West, Central, Southern, and Northeastern regions of the USA.

QIN, L. and L.S. Demski NEURAL SYSTEMS FOR CLASPER CONTROL IN STINGRAYS.

The innervation of the clasper has been studied in several batoids with emphasis on Urolophus halleri. Large myelinated nerves (ca. 10 at diameters of approx. .7mm; #56-65 counting from the vagus) innervate the clasper muscles and skin. Although the same nerves are present in females they are considerably smaller in cross sectional area. In males, low level electrical stimulation (20-150A) of the nerve evokes clasper movements including: rotation, elevation, medial and lateral extension and opening. Stimulation of the spinal cord in the area of the roots of the latter nerves also evoked the movements (<100A with best freq. 3-10 Hz). Filling of nerves 62 and 63 with retrograde tracers confirmed that motor neurons and sensory components of the nerves are at the levels indicated by stimulation. Axons immunoreactive for GnRH are present near the clasper motor neurons, suggesting a supraspinal peptidergic control of the system.

RASMUSSEN, L.E. and S.H. Gruber SERUM LEVELS OF REPRODUCTIVE-RELATED CIRCULATING STEROID HORMONES IN PLACENTAL SHARKS.

For several years we have been examining the levels of reproductively-related steroid hormones in carcharhinid sharks, unusual lower vertebrates possessing the unique attribute of placental viviparity. Our measurements of the serum levels of estradiol (E), testosterone (T), progesterone (P), dihydrotestosterone (D) and corticosterone (C) have established baseline data for these hormones including ranges and means. Our studies have encompassed both immature and adult males and females of 2 sphyrnid and 6 carcharhinid species, with the focal species being the lemon shark Negaprion brevirostris. We have focused on several aspects of reproduction including: 1. hormonal level changes during female and male maturation; 2. serum hormonal levels during the peak breeding season; and 3. hormonal levels during gestation, including levels in serial samples from several free-ranging pre- and post-partum lemon sharks. The data suggest that steroids are important in regulating reproduction in higher mammals are also essential in these cartilaginous fishes and may provide additional models for studying reproductive adaptations.

SAUNDERS, M.W. and G.A. McFarlane AGE-AT-MATURITY OF SPINY DOGFISH (SQUALUS ACANTHIAS) IN THE STRAIT OF GEORGIA, BRITISH COLUMBIA.

A total of 3,068 female dogfish were examined to determine maturity condition. The median age-at-maturity for females calculated using PROBIT analysis was 35.3 years with 95% confidence limits of 0.43 years. AS deterministic age-structures model incorporating information on fecundity, growth and reproduction was used to examine the reproductive strategy of the dogfish. The age-at-maturity reported corresponds to the level that theoretically maximizes lifetime reproductive output for a cohort of dogfish. The implications of these findings to the management of this species are examined.

SCHWABE, C. RELAXIN, SHARKS, AND GENEOLOGY.

During the past ten years we have isolated and sequenced relaxins from elasmobranch ovaries as well as from ovaries of other species including cetaceans. Structural and functional comparison of these relaxins revealed surprising differences and, very conspicuously, a lack of correlation with generally accepted phylogenetic branching patterns. Elasmobranch relaxins differ by the same number of residues from mammalian relaxins as the mammalian relaxins differ from each other. By comparison with the fossil record the evolutionary clock for relaxin therefore runs in error by 300 million years, more than 50% of the total time allotted to macroscopic evolution. Yet relaxins from Odontaspis taurus, Squalus acanthias, and Raja erinacea do effect the symphysis pubis of mice in a hormone-specific way. The structure of cetacean relaxins tops off an intriguing, non-Darwinian story of evolution that is at once telling us that protein structure-based geneology may be an illusion created by a paradigm.

SHERWOOD, N.M. and D.A. Lovejoy GnRH IN CARTILAGINOUS FISH: STRUCTURE, LOCATION, AND TRANSPORT.

The primary structure of gonadotropin-releasing hormone (GnRH) was determined for ratfish (Hydrolagus colliei). Amino acid composition and sequencing analysis in combination with mass spectrometry were used to show that this form of the peptide was identical to a form originally extracted from chicken brains. Both ratfish and dogfish ()Squalus acanthias) have a similar chromatographic and immunological profile suggesting that both species may possess the same form of GnRH. Using an antiserum (GF-4), which recognizes all known molecular species of GnRH, immunohistochemical analysis revealed that only a few positive fibers were found in the ratfish brain. In contrast, GnRH cell bodies occurred in the forebrain and hypothalamus in both dogfish and black skate (Bathyraja kincaidii). In the latter two species, an extensive GnRH fiber system radiated throughout the brain with the exception of the cerebellum. GnRH was detected in the blood of ratfish and big skate (Raja binoculate) suggesting that the transport of GnRH to the pituitary may be different from that of other vertebrates.

SILVA, T.C. and R.P. Lessa SEXUAL DEVELOPMENT OF SPHYRNA TIBURO (PISCES, SPHYRNIDAE) FROM NORTHERN BRAZIL.

A sexual development study was carried out on the basis of 191 specimens of Sphyrna tiburo caught on the north coast of Brazil between 1984 and 1986. Results reveal that taking into account seminal ampullae fullness and claspers condition, the length class of 80.0 cm TL was considered to correspond to the full maturity. Males lever growth showed a discontinuity at the moment where they achieve maturity, which indicates that this organ may play an important role during the reproductive process. Vitellogenic activity starts for females longer than 70.0 cm TL, thereafter individuals with both yellow and white eggs were found. Pregnancy appeared in 90.0 cm TL females, longer specimens were pregnant or not. Liver growth process showed two different phases. A discontinuity was observed at the moment where pregnancy started.

STRONG, W.R., F.F. Snelson, and S.H. Gruber HAMMERHEAD SHARK PREDATION ON STINGRAYS: AN OBSERVATION OF PREY HANDLING BY SPHYRNA MOKARRAN.

During a study of stingrays near Bimini, we observed and filmed the pursuit, attack, and consumption of a southern stingray (Dasyatis americana) by a great hammerhead shark (Sphyrna mokarran). The sharks (ca. 3 m TL) intercepted the fleeing ray (ca. 93 cm DW) and used the underside of its broad snout to batter the ray to the bottom. As the ray resumed flight, the sharks again used the expanded rostrum to pin the ray to the bottom. This time, however, the shark pivoted while the ray was restrained and took a crescent-shaped bite out of the anterior margin of the left pectoral fin. When the ray resumed feeble flight, the shark again pinned it with its head and pivoted, this time taking a symmetrical bite from the right pectoral fin. The shark subsequently circles the incapacitated ray for 24 min. before returning to pick up and finish consuming the prey. Although the function of the expanded cephalic lobes of sphyrnid sharks has been the subject of much conjecture, this is the first observation of the use of the head in prey handling. Many authors have pointed out that both S. mokarran and S. zygaena consume large numbers of batoids. The behaviors involved in this predatory act, especially the use of the expanded head and the placement of the initial incapacitating bites, suggest an adaptive strategy for maximizing predatory efficiency while minimizing the risk of injury when feeding on rays.

WALTON, P.J. and J.D. McEachran ONTOGENETIC DEVELOPMENT OF NARCINE BRASILIENSIS IN RELATION TO THE ELECTRIC ORGANS.

Among the various electric fishes are the Torpediformes (electric rays), whose phylogenetic relationship to the rest of the Order Batoidea is obscured by the large electric organs that dominate the pectoral region, and demand skeletal adaptations. As a representative of this group Narcine brasiliensis was examined in order to characterize the ontogenetic relationship between the electric organs and the developing embryo. Research focused on development of body shape (by Morphometric Analysis) and skeletal structures (by clearing and staining). In the range of specimens examined, there was no significant shape change, while skeletal structures forming in this range show great accommodation to the electric organs. Results indicate that the Torpediform "shape" emerges early in ontogeny, even before the electric organs have fully formed; therefore, future research should focus on ontogeny in early stages in order to observe a more generalized state of development in this group.

WOURMS, J.P. MAXIMIZATION OF EVOLUTIONARY TRENDS FOR SELACHIAN PLACENTAL VIVIPARITY IN THE SPADENOSE SHARK, SCOLODON LATICAUDUS.

Placental viviparity has evolved in S. laticaudus to a degree that rivals eutherian mammals. Its egg, the smallest of any sharks (1 mm, 0.065 mg), is nearly yolk free. Cleavage and gastrulation are modified. Implantation is early (at 3 mm) and gestation short (5-6 months). With a gestational weight increase of 10,000x, term embryos (130-150 mm, 600-900 g) are extreme matrotrophes. Hemotrophic placental nutrient transfer occurs across a unique uterine implantation site, termed the trophonematous cup, at which maternal blood bathes the embryonic yolk sac placenta. the latter is solid and filled with a stalk that contains the vitelline vessels but lacks a yolk duct. Its surface is amplified by many long villous appendiculae, each comprised of a vascular core that terminates in surface capillary beds invested by a simple squamous epithelium. Appendiculae are sites of metabolite transport and display design principles that are similar to those of the uterine trophonemata of matrotrophic rays, but are unlike the appendiculae of other placental sharks.

YANO, K. REPRODUCTIVE BIOLOGY OF SLENDER SMOOTH HOUND, GOLLUM ATTENUATUS COLLECTED FROM THE SEAMOUNT AROUND NEW ZEALAND WATERS.

This study presents the result of reproductive biology of slender smooth hound, Gollum attenuatus. This species belongs to the family Proscylliidae, and can be distinguished other relative genera by slender body and bell-shaped snout. 740 specimens were caught with bottom longline from the seamount around New Zealand waters. The sharks ovulated about 100 ova at a diameter of 5-8 mm. One egg capsule had 50-80 ova. However, development of embryo in each egg capsules was only one. On the other hand, many other ova are mixed in the capsules and are probably used to nutrients of development of the embryo. The embryos has external yolk sac. Size at maturity are also discussed.

ZHENG, W. REPRODUCTIVE BIOLOGY OF THE GUITARFISH, RHINOBARUS HYNNICEPHALUS RICHARDSON.

Reproductive biology of the guitarfish, Rhinobatos hynnicephalus from Xiamen coastal waters is described. Males have two functional testes. Spermatogenic cells in different seminiferous follicles are at different developmental stages while those in the same follicle are at the same stage. The development of claspers suggests that males mature at 380-400 mm TL. Females have two functional ovaries which attain maturity in May or June. Ovarian egg diameters show that females mature at 420-440 mm TL. Mature eggs of 22-24 mm in diameter are ovulated in July. Gestation takes 12 months and embryos are released at about 160 mm TL. Pregnancy takes place again soon after parturition. The number of embryos per uterus has a positive relation with the adult total length. The sex ratio of embryos is about 1:1.