Experimental pathogenicity of reovirus 13p2 for juvenile American oysters Crassostrea virginica (Gmelin) and bluegill fingerlings Lepomis macrochirus (Rafinesque)

Abstract. A viral agent (13p₂), isolated from clinically normal juvenile American oysters ( Crassostrea virginica ) and characterized as a new serotype of reovirus, was tested to determine if it could replicate and produce disease in experimental juvenile oysters. Because the virus replicated well in the bluegill fry (BF-2) fish cell line, fingerling bluegills Lepomis macrochirus were included in the pathogenicity experiments. Exposure of oysters to the 13p₂ virus in ambient seawater resulted in no significant mortality and no increased virus titres or histological lesions. Virus particles were not observed in tissues of exposed oysters when examined with transmission electron microscopy (TEM). Intraperitoneal inoculation of the 13p₂ virus into bluegills resulted in 44% mortality associated with a focal necrotic hepatitis. Evidence of virus replication, when evaluated histological or by virus titration, was observed in 94% of 32 inoculated fish. Samples of infected livers examined with TEM revealed typical cytoplasmic arrays of 13p₂ virus particles in affected hepatocytes. Rising virus titres and hepatic lesions also occurred in bluegills exposed to water containing the 13p₂ virus. These results indicated the natural host of the 13p₂ virus was not the American oyster, but that it was a significant pathogen for at least one fish species.     

Colorimetric determination of poly(N-vinyl-2-pyrrolidone) in contact lens solutions.

A rapid colorimetric method is presented for the quantitative determination of poly(N-vinyl-2-pyrrolidone) in contact lens solutions. The method is simple, requires no sample pretreatment, and uses only a small volume of sample. The procedure is based on the measurement of the net absorbance of a poly(N-vinyl-2-pyrrolidone)- Congo red complex at 545 nm. An accuracy of greater than +/- 4% was obtained for the concetnration ranges usually found in contact lens solutions with a minimum detection level of 10 ppm. The method is useful as a screening procedure for solutions of unknown composition and as a quality assurance procedure for routine determinations.     

Nitrous oxide emission from soils at low moisture contents

The production of nitrous oxide by soils was studied over short periods at a range of moisture contents up to field capacity with a highly-sensitive gas Chromatographic method.Nitrous oxide (N₂O) was emitted from all soils studied at all soil moisture contents, which ranged from air dry to field capacity. The rate of emission increased with increasing moisture content and with increasing temperature up to 37°C.The evolution of N₂O was not due to displacement of soil air during wetting. It was inhibited by HgCl₂ and toluene, and was prevented by formaldehyde and autoclaving. Thus it appeared to be due to microbiological processes.The results of experiments with nitrification and denitrification inhibitors suggest that a considerable part of the N₂O was produced by the oxidation of ammonia. Production by denitrification of nitrate cannot be ruled out. The relative importance of these two mechanisms probably depends on the moisture and oxygen content of the soil.It is concluded that the microbial production of N₂O is continuous in soil at all moisture contents. The process at low moisture contents constitutes an important component in the cycle which maintains the N₂O concentration in the atmosphere.     

Hepatomas in Atlantic tomcod Microgadus tomcod (Walbaum) collected in the Hudson River estuary in New York

Abstract. Incidental observations of Atlantic tomcod during routine laboratory processing revealed that a portion of the adult population collected during the 1977–78 spawning season had enlarged livers containing dark coloured tumours and other abnormalities. Of the total of 264 livers collected between 16 January and 27 February 1978 and grossly examined for prevalence of abnormalities, 25% appeared to contain neoplastic nodules and hepatocellular carcinoma. One liver contained a massive tumour (7 × 12 mm) that involved approximately 60% of the liver. The exact causes of the high prevalence of hepatocellular carcinoma are unknown but poly-chlorinated biphenyls (PCBs) are suspected of having a possible role. The Hudson River is known to contain elevated concentrations of PCBs. Twelve tomcod livers from the 1977–78 spawning population representing both normal and hepatoma conditions contained concentrations of PCBs ranging from 10–9 to 98–2 ppm (mean of 37–5 ppm).     

Regrowth of ryegrass swards subject to different cutting regimes and stocking densities

A cutting experiment was carried out on a sward of S23 perennial ryegrass to study the effect of different defoliation regimes on regrowth and the factors affecting regrowth. The defoliation frequencies and intensities encompassed the range commonly found on continuously stocked pastures. The defoliation regimes produced swards of contrasting growth form with regrowth characteristics which differed in respect of senescence loss, fall in water-soluble carbohydrate concentration, residual leaf area index, photosynthesis per unit leaf area index and photosynthesis per unit area of land. Regrowth was most closely related to the latter. These results were used to interpret data for net canopy photosynthesis of continuously grazed pastures.