The structure of the testis of the mullet, Liza dumerili (Teleostei; Mugilidae) with special reference to spermatogenesis

The macro-morphology and the histology of the testis of Liza dumerili are described with special reference to the various types of spermatogenic cells. L, dumerili possesses typical teleost testes. The only peculiarity is the conspicuous main sperm duct, which runs on the surface (medio-ventral) along the entire length of each testis. Testicular lobules contain cysts in which highly synchronized spermatogenesis takes place. Three generations of spermatogonia are evident, although further subdivisions are possible. Four types of primary spermatocytes are recognized. Typical interlobular Leydig cells appear in close association with small blood vessels. “Lobule-boundary cells” seem to be present but were only evident in I µm Epon sections

The breeding cycle of male Liza dumerili (Teleostei: Mugilidae) in the mouth of the Swartkops wstuary

The breeding cycle of male Liza dumerili was studied in the Swartkops Estuary using a visual index, a gonosomatic index and a histological index. Histological studies were superior to any other means of establishing the breeding cycle in detail. Male fish were in the inactive or non-breeding state during the winter months. During early spring the gonads started to mature and full ripeness was attained during December and January. January and February were the main spawning months, and in addition a short spawning peak might be present during October. The seasonal appearance of spermatogonia in the testes is discussed

Exploring the temporally resolved electron density evolution in EUV induced plasmas

We measured for the first time the electron density in an Extreme Ultra-Violet induced plasma. This is achieved in a low-pressure argon plasma by using a method called microwave cavity resonance spectroscopy. The measured electron density just after the EUV pulse is $2.6\cdot10^{16}$ m$^{-3}$. This is in good agreement with a theoretical prediction from photo ionization, which yields a density of $4.5\cdot10^{16}$ m$^{-3}$. After the EUV pulse the density slightly increase due to electron impact ionization. The plasma (i.e. electron density) decays in tens of microseconds.Comment: 3 pages, 4 figure

Growth and production of Bullia rhodostoma on an open sandy beach in Algoa Bay

The plough shell, Bullia rhodostoma (Mollusca: Gastropoda), has been studied on an open sandy beach where it is a common scavenger. Samples taken over a year indicate hatching of young individuals from December to February. They reach a length of about 10 mm after 1 year and 40 mm after 10 years. The von Bertalanffy growth equation is Lt = 47 (1 - e-0,19(t+0,23)) and the annual mortality rate is 0,79. Mean decalcified dry biomass is 209 mg m-2 and production by growth 189 mg m-2 y-1 giving a P/B of 0,9. Most production by adults (>15 mm shell length) goes into reproduction, particularly In the females which grow larger than the males. Production by reproduction is estimated to be about 135 mg m-2 y-1. Average calorific values are 19,04 kJ g-1 dry tissueDie ploegskulp, Bullia rhodostoma (Mollusca: Gastropoda), is op 'n oop sandstrand bestudeer waar dit 'n algemeen teenwoordige aasvreter is. Monsters wat oor 'n jaar geneem is, dui aan dat die jong individue tussen Desember en Februarie uitbroei. Hulle bereik 'n lengte van ongeveer 10 mm na 1 jaar en 40 mm na 10 jaar. Die Von Bertalanffy groeivergelyking is Lt = 47 (1 - e-0,19(t+0,23))) en die jaarlikse mortaliteitstempo is 0,79. Gemiddelde kalklose drofi biomassa is 209 mg m-2 y-1 wat 'n P/B van 0,9 gee. Die meeste volwasse (>15 mm skulplengte) produksie is in die vorm van voortplanting, veral in die wyfies wat groter as die mannetjies word. Produksie deur voortplanting is omtrent 135 mg m-2 y-1 Gemiddelde kaloriewaardes is 19,04 kJ g-1 droe weefsel

Studies on the motility and cryopreservation of rainbow trout (Salmo gairdneri) spermatozoa

The very short duration of vigorous movement (1½ to 7 min) in fresh water and physiological solutions make trout spermatozoa difficult subjects for cryopreservation studies. Solutions consisting of 250 to 280 mmol sucrose and 5 to 12% dimethyl sulphoxide (DMSO) (4 parts) did not activate trout spermatozoa (1 part), but after dilution with fresh water vigorous motility could be fully restored. These sucrose·DMSO solutions were employed in cryopreservation studies. Using straws and a fast freezing - fast thawing procedure, post· thaw dilution with fresh water resulted in 25% - 60% of spero matozoa becoming motile, all with vigorous forward progression. Some existing methods for the cryopreservation of other freshwater fish spermatozoa were repeated on trout without success

Broadband modelling of short gamma-ray bursts with energy injection from magnetar spin-down and its implications for radio detectability

The magnetar model has been proposed to explain the apparent energy injection in the X-ray light curves of short gamma-ray bursts (SGRBs), but its implications across the full broadband spectrum are not well explored. We investigate the broadband modelling of four SGRBs with evidence for energy injection in their X-ray light curves, applying a physically motivated model in which a newly formed magnetar injects energy into a forward shock as it loses angular momentum along open field lines. By performing an order of magnitude search for the underlying physical parameters in the blast wave, we constrain the characteristic break frequencies of the synchrotron spectrum against their manifestations in the available multi-wavelength observations for each burst. The application of the magnetar energy injection profile restricts the successful matches to a limited family of models that are self-consistent within the magnetic dipole spin-down framework.We produce synthetic light curves that describe how the radio signatures of these SGRBs ought to have looked given the restrictions imposed by the available data, and discuss the detectability of these signatures with present-day and near-future radio telescopes. Our results show that both the Atacama Large Millimetre Array and the upgraded Very Large Array are now sensitive enough to detect the radio signature within two weeks of trigger in most SGRBs, assuming our sample is representative of the population as a whole. We also find that the upcoming Square Kilometre Array will be sensitive to depths greater than those of our lower limit predictions.Comment: 15 pages, 4 figures, 6 tables, accepted for publication in MNRA

Objective and perceived availability of physical activity opportunities: differences in associations with physical activity behavior among urban adolescents

ABSTRACT: BACKGROUND: This study examined the associations of the perceived and objective environment with adolescent engagement in sports activities and walking and cycling in leisure time. It also explored the degree of agreement between objective and perceived availability of physical activity (PA) facilities in neighborhoods. METHODS: Cross-sectional data on physical activity, the perceived availability of physical activity opportunities (perceived physical environment) was assessed through a questionnaire and the objective availability of PA opportunities (objective physical environment) was obtained through GIS data. The final sample included 654 adolescents with a mean age of 14.1 (SD = 1.2) years. RESULTS: Perceived availability of sports facilities and parks was significantly associated with engaging in sports (OR: 1.73; 95% CI: 1.16-2.56) and with walking and cycling in leisure time (OR: 1.66; 95% CI: 1.07-2.57) respectively. Agreement between objective and perceived environment was low to moderate with Kappa values ranging from -0.005 to 0.053. CONCLUSION: The perceived environment was the stronger correlate of PA behavior among adolescents. There were substantial differences between assessments of objective and perceived physical environmen