The blue stingray, Dasyatis marmorata capensis is an important recreational shore angling species, especially amongst tournament anglers, in South Africa. The taxonomy and aspects of the biology of this species were investigated from specimens collected between March 1987 and May 1989, from various localities along the southern African coastline. Morphological comparisons were made between Dasyatis pastinaca, Dasyatis marmorata and the local variety. The results indicated that the local variety is different to D. pastinaca in colouration, disc length size, and vertebral and radial counts. The proposed new sub-species Dasyatis marmorata capensis is closest to Dasyatis marmorata of the north-eastern Atlantic coast, but differs in snout angle, disc length and snout to vent length. Analysis of catch per unit of effort data revealed that the blue stingray exhibits distinct seasonality. Adult and sub-adult fish undertake an annual onshore/offshore migration and invade the inshore region between spring and summer, while juveniles remain offshore and utilize this zone as a nursery area. Length-at-age and growth rates for both sexes were estimated from bands formed seasonally in the vertebral centra. The derived von Bertalanffy growth parameters indicated that females reach a greater asymptotic size (913.8 mm DW) and have a slower growth rate (K = -0.07) than males (531.8 mm DW, K = -0.17). Growth rates of juvenile captive specimens compared favourably with back calculated values, at approximately 65 mm/year, for the first year of growth. Dasyatis marmorata capensis is an aplacental viviparous elasmobranch with a well defined annual breeding cycle. Young are released , at a size of 170-200 mm DW, from October to December after a gestation period of approximately nine months. An average fecundity of 3.07 was calculated . Examination of gonadal development indicated that sexual maturity is first attained at a size of 408 and 500 mm DW in males and females, respectively, corresponding to ages 4.5 and 7 years. Size-related food habits were determined independently from three depth zones. The major prey items for each size class were directly related to the abundance of the infauna of the different depth zones. Polychaeta, amphipoda and stomatopoda were the major prey items in the offshore zone. In the nearshore zone, the dominant prey species were Balanoglossus capensis and Callianassa spp .. The high incidence of empty stomachs and the presence of prey items which occur in greatest abundance beyond the surf zone indicated that this zone is not utilized for the purposes of feeding.

A diagnostic characteristic of stingrays in the Family Dasyatidae is the presence of a defensive, partially-serrated spine located on the tail. The objective of this study is to assess the impacts of caudal spine morphology on puncture and withdrawal performance from two stingrays, Hypanus sabinus and Hypanus say. Spines have highly variable morphology. I used an Instron E1000 materials tester to quantify the puncture and withdraw forces from porcine skin, a model for human skin. I found no significant differences between puncture and withdraw or between the species. By incorporating micro-CT scanning to quantify mineralization density, I quantified more mineralization along the shaft of the spine. Equal puncture and withdraw forces and increased mineralization along the spine shaft may create a stiffer structure that can be a persistent predator deterrent. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

No description available.

Thesis (M.S.)--University of West Florida, 2009. / Submitted to the Dept. of Biology. Title from title page of source document. Document formatted into pages; contains 49 pages. Includes bibliographical references.

In mammals distinct steroid hormones termed mineralocorticoids (MCs) and glucocorticoids (GCs) regulate hydromineral balance and the stress response, respectively. In contrast, it is thought that a single corticosteroid, 1[alpha]-hydroxycorticosterone (1[alpha]-B) serves as both a GC and MC in elasmobranchs. I investigated the putative dual MC and GC roles of 1[alpha]-B by examining ex vivo regulation of interrenal 1[alpha]-B synthesis by osmoregulatory and stress hormones in the euryhaline stingray Dasyatis sabina. A commercial enzyme-linked immunoassay was adapted for the quantification of 1[alpha]-B. I also isolated cDNA sequences encoding two rate-limiting steroidogenic enzymes, the steroidogenic acute regulatory protein (StAR) and P450 cholesterol side-chain cleavage (P450scc), and characterized the steroidogenic activity of the encoded proteins using a heterologous expression system. Both the stress hormone adrenocorticotropic hormone (ACTH) and the antinatriuretic peptide angiotensin II (ANG II) were potently steroidogenic in ex vivo interrenal cultures, whereas C-type natriuretic peptide (CNP) inhibited 1[alpha]-B synthesis. StAR and P450scc mRNA levels were increased by 24 h incubation with ACTH and decreased by both ANG II and CNP. To examine changes in osmoregulatory hormone systems that impinge upon 1[alpha]-B synthesis, I also isolated the cDNA sequences of the ANG II and CNP receptors, AT and NPR-B. Both AT and NPR-B mRNA levels were significantly elevated in osmoregulatory tissues of freshwater (FW; Lake Monroe, FL) versus saltwater (SW; Corpus Christi Bay, TX) populations of D. sabina. Interrenal StAR and NPR-B mRNA levels were also significantly higher in FW individuals. The physiological roles of 1[alpha]-B were further investigated in vivo by examining the effects of stress and FW transfer on interrenal synthesis of 1[alpha]-B. Plasma 1[alpha]-B and glucose were significantly elevated by hook-and-line capture stress, indicating that 1[alpha]-B acts in classical GC fashion to facilitate the stress response. In contrast, 1[alpha]-B was significantly decreased 24 h after SW-FW transfer. In light of the osmotic strategy of euryhaline elasmobranchs, this result is consistent with a MC role for 1[alpha]-B. Taken together, the results of this research strongly support a dual role for 1[alpha]-B in facilitating both hydromineral balance and the stress response in elasmobranchs. / text

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

No description available.

Thesis (M.Tech.: Homoeopathy)-Dept. of Homoeopathy, Durban University of Technology, 2008. xiii, 159 leaves / The purpose of this study was to determine the effects of Gymnura natalensis in the thirtieth centesimal potency on healthy volunteers and to record the signs and symptoms produced by the volunteers during the study. These signs and symptoms determined the therapeutic indications of this remedy for its prescription according to the homoeopathic Law of Similars. A further aim of this study is a proposed group analysis of a natural family of biologically unrelated sea animal remedies (Mangialavori, 2002) with the aim of highlighting themes, similarities and differences within the group.

Mini-dissertation submitted in partial compliance with the requirements for the Master’s Degree in Technology: Homoeopathy in the Department of Homoeopathy at the Durban University of Technology, 2008. / The aim of this study was to determine the effect of Gymnura natalensis 30CH on healthy volunteers, and to record the signs and symptoms produced, so that it may be prescribed to those requiring it according to the Law of Similars. The other aims of this study were to compare the proving symptoms of Gymnura natalensis 30CH to the toxicology of stingray venom and to analyze the remedy picture in terms of the Doctrine of Signatures. It was hypothesised that the thirtieth centesimal potency of the remedy would produce clearly observable signs and symptoms in healthy volunteers (provers). It was further hypothesised that the above signs and symptoms would show a correlation to the toxicology of stingray venom and to the Doctrine of Signatures. The homoeopathic proving of Gymnura natalensis took the form a double-blind, randomised, placebo-controlled trial. The selected proving potency was the thirtieth centesimal potency. A total population of 30 suitable and consenting volunteers participated in this trial. Twenty percent of this population was randomly administered a placebo-control substance. The collection of data from the provers took the form of a journal which was kept by each prover in which their proving signs and symptoms were recorded over a period of five weeks after the administration of the remedy or placebo. On completion of the proving, each journal was assessed by the researcher to determine the suitability of the recorded symptoms for inclusion in the materia medica of Gymnura natalensis. These symptoms were then translated into the language of the materia medica and repertory and a remedy picture was then formulated. Data from case histories, physical examinations (Appendix D) and group discussions were also taken into account during the analysis of the proving the symptoms. A concurrent proving study of Gymnura natalensis, conducted by Naidoo (2008), focused on comparing the symptoms of this remedy to those of other existing remedies that were derived from the sea. A variety of mental, emotional and physical symptoms were extracted from the proving study of Gymnura natalensis. The main mental and emotional symptoms of the remedy included anxiety, irritability, depression, a feeling of disconnection, spaciness of the mind and dreams of events and incidents of the past. The characteristic physical symptoms obtained from the proving included headaches, a reduction of pre-menstrual symptoms, heart palpitations, skin eruptions on the back, low energy levels, tiredness and sleep abnormalities. Symptoms that showed a correlation to the toxicological symptoms of stingray envenomation included frequent urination, muscular cramps, heart palpitations, laboured breathing, fever and copious night sweats. The symptoms that characterised the remedy in terms of the Doctrine of Signatures included anxiety, instinctive behaviour, the desire to be alone, feelings of disconnection, detachment and isolation and skin eruptions on the back. The investigation confirmed the hypothesis that Gymnura natalensis would produce clearly observable sings and symptoms in healthy volunteers. The correlation of the proving symptoms to the toxicology of stingray venom and the Doctrine of Signatures provided a clarification of the remedy picture to assist in the understanding and prescription of this remedy. / M

Elasmobranch fishes use electroreception to detect electric fields in the environment, particularly minute bioelectric fields produced by potential prey. A single elasmobranch family (Potamotrygonidae) is composed of obligate freshwater stingrays endemic to the Amazon River. A freshwater existence has imposed morphological adaptions on their electrosensory system due to life in a high impedance medium. Because their electrosensory morphology differs from their marine relatives, freshwater stingrays may demonstrate corresponding differences in behavioral sensitivity. The objective of this study was to quantify behavioral sensitivity of the obligate freshwater stingray Potamotrygon motoro to prey-simulating voltage. The voltage produced by common teleost prey of P. motoro were measured and replicated for behavioral trials. The best response was 10.62 cm, and the smallest voltage gradient detected was 0.005 mVcm-1. This sensitivity is reduced compared to marine species. The conductivity of the medium, more so than ampullary morphology, may dictate sensitivity of the elasmobranch electrosensory system. / by Lindsay L. Harris. / Thesis (M.S.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.