Growth of pen reared pink salmon fry,Oncorhynchus gorbuscha,feeding on available marine zooplankton

Pink salmon fry, Oncorhynchus gorbuscha, were held in a small floating net pen for nearly 7 weeks. The pen was moored in a narrow channel where tidal current velocities reach values near 0.4 m/s. The fry were maintained solely by marine zooplankton carried into the enclosure by surface currents.Samples of approximately 100 fry were removed weekly from the pen to monitor growth and diet. For the 1049 fry which began the experiment, fork length ($\text{FL}$) averaged 32.7 mm and wet weight ($\text{W}$) 0.23 g. Forty-eight days later 330 fry remained in the pen; $\text{FL}$ had increased to 44.1 mm and $\text{W}$ to 0.76 g. Natural mortality in the pen was less than 2% during this period.     

Bacteriological findings regarding the hygienic safety of poultry litter intended as an ingredient of feeds for ruminants

An investigation of poultry litter intended for use in farm feeds showed that 0,37%, 0,49%, 0,25% and 12,3% of the 813 samples tested were contaminated with Clostridium spp., haemolytic Escherichia coli, Staphylococcus aureus and 21 different species of Salmonella. The findings clearly underline the hygienically dangerous nature of crude poultry litter. The practical implications of the results are briefly discussed, particularly in view of current regulations.     

Attenuation of turkey meningo-encephalitis virus in BHK21 cells

Turkey meningo-encephalitis virus was adapted to BHK21 cell culture. Cytopathic effects were characterized by rounding and detachment of cells within 48 hours. Attenuation was achieved by 41 successive passages in BHK21 cell cultures. Turkeys and Japanese quail (Coturnix coturnix japonica), kept under laboratory conditions and inoculated with the attenuated virus, did not develop symptoms of turkey meningo-encephalitis but reacted by the production of haemagglutination inhibition antibody. They resisted intracerebral challenge with pathogenic strains of turkey meningo-encephalitis virus.     

Flaviviruses in South Africa: diagnostic procedures

Employing rabbit immune serum, 10 flaviviruses known to be present in South Africa could be divided into 5 serological subgroups. The subgroups conform to the general pattern described for the group. Sera from experimentally infected calves and lambs were monospecific in neutralization tests, but cross-reacted in haemagglutination inhibition tests. These results suggest that sheep and cattle sera from the field can best be tested by microneutralization tests. The greater sensitivity of embryonated hen's eggs for some viruses and of one-day-old mice for other viruses necessitates the employment of both systems for the isolation of flaviviruses from field specimens.     

Patterns of exotic plant invasions in fragmented urban and rural grasslands across continents

Linear native grassland remnants in fragmented landscapes are usually at a great risk of exotic species invasion from their edges. Changes in species distribution near habitat edges are extensively studied in ecology as knowledge about edge responses is important to understand the development of patterns and processes in landscapes. However, elucidating robust general principles for edge effects has been difficult as species responses to habitat edges are highly variable and dependent on a large number of attributes which affect the function and structure of edges and therefore the distance that edge effects penetrate into fragmented natural vegetation. The objective of this study was to investigate the generality of exotic species invasion patterns from edges in native grassland patches surrounded by urban and rural landscapes. This was done by comparing the results of research from Victoria, Australia with a similar study from North-West Province, South Africa. Despite their occurrence on different continents, the grasslands are floristically and structurally similar and are dominated by the same grass species. Invasion patterns were quantified using two spatial statistics methods; block kriging and spatially constrained clustering. Two distinct patterns of exotic species invasion were identified in native grassland remnants in South Africa and Australia, namely exotic species invasion from the edge where the cover of exotic species increased with increasing proximity to the edge and a pattern that suggests that gap phase vegetation dynamics may also drive exotic species invasion at urban grasslands. Although urbanization and weed invasions are complex processes similar patterns of exotic species invasion in urban grasslands were found in two different continents suggesting that general patterns may occur. Implications of this for the conservation of native grasslands in contrasting landscapes are discussed.