Detection of Aphanomyces invadans and epizootic ulcerative syndrome in the Murray‐Darling drainage

Epizootic ulcerative syndrome was diagnosed, and the presence of Aphanomyces invadans confirmed, from an outbreak of clinical disease in wild‐caught bony bream (Nematalosa erebi) from the Darling River near Bourke, in New South Wales, Australia, during 2008. This confirms a significant extension of the agent beyond its historical range.     

Ovarian contractility in reared gilthead seabream (Sparus aurata L.) in different phases of the reproductive cycle

Spontaneous ovarian tunica albuginea contractility was evaluated in gilthead seabream (Sparus aurata L.) at different phases of the reproductive cycle. Fourteen adult females were sampled from February to November 2012 in a commercial fish farm, and ovaries were removed and processed for histological and contractility analyses. Fish reproductive stages were evaluated on haematoxylin–eosin-stained ovary sections or by simple macroscopic observation of hydrated oocytes in spawning individuals. Tunica albuginea spontaneous contractility was recorded by using ovary wall strips mounted in an organ bath containing modified Ringer’s solution. Ovary macro- and microscopic analyses allowed the identification of three different reproductive conditions: vitellogenesis, spawning and regressing. The gilthead seabream tunica albuginea was capable to contract spontaneously, and significant differences were found in mean contraction amplitude among the three reproductive states, with the highest value recorded in individuals in regressing condition and the lowest in individuals at spawning stage. No differences in mean contractility frequency among the three different groups were found. Possible involvement of spontaneous contractility in facilitating developing follicle advancement towards the ovarian lumen within the ovary and in supporting recovery of regressing ovaries may be hypothesized. The low contractility observed during the final oocyte maturation and spawning phases does not seem to support a role of tunica albuginea during ovulation, which could conversely involve theca cell contraction. Alternatively, possible single instantaneous contractions of tunica albuginea muscle fibres, not detected in the present study, could occur during ovulation in response to neuro-hormonal stimulations; a role of abdominal wall musculature in ovary “squeezing” and consequent release of ovulated eggs cannot be excluded.     

Hydrogen radicals, nitrogen radicals, and the production of O3 in the upper troposphere

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.     

Simulation modelling as a tool for evaluating surveillance programmes for detection of the Asian honeybee mite (Varroa destructor) in the South Island of New Zealand

AIM: To use a simulation model of the spread of the Asian honeybee mite (Varroa destructor) amongst apiaries, to evaluate a series of detection surveillance programmes for the South Island of New Zealand.

METHODS: Five potential incursion sites into the South Island were selected. A stochastic spatial simulation model, Varroa_sim, was adapted to simulate spread of the mite from these sites as a series of silent-phase propagating epidemics. The study population comprised all apiaries in the South Island registered in the Ministry of Agriculture and Forestry's (MAF's) apiary database in 2003. Six different surveillance programmes were simulated to try and detect the mite. Three of these were the actual multi-stage sampling plans conducted during the autumn (March–May) of 2001, 2002 and 2003, and the other three involved simple random sampling with sampling fractions equivalent to the actual numbers of apiaries tested in each of those years. The relative performances of the different surveillance plans were evaluated in terms of their ability to detect the mite early before it had spread too far and whilst there might still be a chance of eradication.

RESULTS: There were 13,798 registered apiaries in the South Island with valid map coordinates in the apiary database at the time of the study. The model generated 50 epidemics against which the various surveillance programmes were evaluated. The actual surveillance programmes conducted during the autumn of 2001 and 2002 generally performed fairly well in detecting the mite. The programme conducted in autumn 2003 detected the mite reasonably well in high-risk areas, but was very poor in low-risk areas. The simple random sampling strategies performed surprisingly well, and their relative rankings were proportional to the sampling fractions employed.

CONCLUSIONS: This study showed the value in using a spatial simulation model to generate plausible silent-phase epidemics, against which detection surveillance programmes could be evaluated, in ways that would otherwise not be possible.