Effects of acute environmental and handling exposure on physiology and fillet quality of market‐sized Channel Catfish

Catfish Ictalurus spp. are subjected to stressful conditions during harvest, which may be linked to fillet coloration and quality. Poor water quality in ponds, socks or hauling tanks, as well as handling stress, have been suggested to cause red fillets in catfish; however, chronic exposure has not resulted in red fillets. Short‐term occurrences of extreme poor water quality, particularly low dissolved oxygen, high carbon dioxide and high temperature, may occur in ponds or during harvest. Therefore, market‐sized Channel Catfish Ictalurus punctatus were acutely exposed (12 hr) to one of the three water quality treatments while confined during a simulated socking procedure and evaluated for stress responses by means of change in blood parameters and fillet quality. In fish subjected to the extreme treatment, hematocrit, plasma cortisol, glucose and lactate levels increased, with 22% mortality, indicating highly stressful conditions. In fish subjected to moderate and typical (control) treatments, cortisol increased but a lack of change or decrease in glucose and lactate indicated minimal anaerobic metabolism. Only one red fillet was produced by the extreme treatment and two by the typical treatment; therefore, the results suggest red fillets are not a product of poor water quality compounded by handling during harvest.     

Synthesis and Characterization of 2-Decenoic Acid Modified Chitosan for Infection Prevention and Tissue Engineering

Chitosan nanofiber membranes are recognized as functional antimicrobial materials, as they can effectively provide a barrier that guides tissue growth and supports healing. Methods to stabilize nanofibers in aqueous solutions include acylation with fatty acids. Modification with fatty acids that also have antimicrobial and biofilm-resistant properties may be particularly beneficial in tissue regeneration applications. This study investigated the ability to customize the fatty acid attachment by acyl chlorides to include antimicrobial 2-decenoic acid. Synthesis of 2-decenoyl chloride was followed by acylation of electrospun chitosan membranes in pyridine. Physicochemical properties were characterized through scanning electron microscopy, FTIR, contact angle, and thermogravimetric analysis. The ability of membranes to resist biofilm formation by S. aureus and P. aeruginosa was evaluated by direct inoculation. Cytocompatibility was evaluated by adding membranes to cultures of NIH3T3 fibroblast cells. Acylation with chlorides stabilized nanofibers in aqueous media without significant swelling of fibers and increased hydrophobicity of the membranes. Acyl-modified membranes reduced both S. aureus and P. aeruginosa bacterial biofilm formation on membrane while also supporting fibroblast growth. Acylated chitosan membranes may be useful as wound dressings, guided regeneration scaffolds, local drug delivery, or filtration.     

Size dependent early salinity tolerance in two sizes of juvenile white sturgeon,Acipenser transmontanus

The objective of this study was to investigate the influence of size on salinity tolerance in 1 year old juvenile white sturgeon. Two sizes of sturgeon (10 and 30 g) from the same spawning event (thus reducing confounding effects of genetic make-up and size) and reared in the same environment were exposed to a salinity of 0, 8, 16, 24, or 32 ppt for up to 120 h. Both 10 and 30 g fish exhibited > 93% mortality within 24 h after transfer to 24 or 32 ppt, regardless of whether they were transferred directly from freshwater (FW) or following a 48 h pre-treatment period at 16 ppt. Direct transfer from FW to 16 ppt was associated with 25 to 30% mortality, indicating that these fish have some ability to tolerate large changes in salinity for up to 5 days at this stage. Following exposure to 8 and 16 ppt, an elevation in plasma osmolarity, [Na⁺], and [Cl^?] was observed between 24 and 72 h in both 10 and 30 g sturgeon, but plasma ions and osmolarity in surviving fish at 120 h were not significantly different between groups held at 0, 8, and 16 ppt. Despite being unprepared for either direct or stepwise transfer to salinities of 24 ppt or greater, size confers some ionoregulatory advantage, as mortality occurred more slowly and the degree of ionoregulatory perturbation was less in 30 g than 10 g fish over the course of the exposures. It is not known whether the apparent advantage of size is related to a size-dependent development of ionoregulatory capacity or due to social status which can also influence ionoregulatory capacity, but age and genetic differences did not likely contribute to this size effect.     

Isotope-edited nuclear magnetic resonance: novel methodologies for investigating metabolism

While the use of NMR and stable isotopes in metabolism studies is hardly new, it is only recently that isotope-edited NMR spectroscopy has been applied in kinetic studies of glyphosate metabolism of soil microbes. NMR can detect multiple species simultaneously and non-destructively, yielding valuable information on structural identification of metabolites. T riple R esonance I sotope ED ited spectroscopy (TRIED), [²H]NMR, and [²H–¹³C] INEPT (I nsensitive N ucleus E nhancement through P olarization T ransfer) are three isotope-edited techniques which have been used in combination to examine the microbial degradation of glyphosate (N-phosphonomethylglycine). Using ¹³C- and ¹⁵N-labeled glyphosate, TRIED can detect multiple metabolites in crude matrices at submicrogram levels, an improvement over earlier techniques where milligrams were needed. It can detect 500 nanograms of ¹³C–¹⁵N-labeled compound in a crude sample (1 : 1400 mass ratio), only a few hours work being required. [²H]NMR and [²H–¹³C]INEPT were also used as complementary techniques to further examine metabolites whose ¹³C–¹⁵N bond has been cleaved. The three-isotope-edited methods produced results consistent with both radioactivity and HPLC analyses. Accordingly, we are able to detect minute levels of metabolites in the presence of complex mixtures, minimizing the costs and time of sample purification. ©1999 Society of Chemical Industry     

Streamflow environment predicts divergent life history phenotypes among populations of the Blacktail Shiner Cyprinella venusta: Temporal stability of a large‐scale pattern

Egg size variation among 16 Gulf Coast populations of Cyprinella venusta, the Blacktail Shiner, previously was shown to be significantly correlated with annual stream runoff. In this study, we examined egg size across multiple years and seasons in a subset of the original populations, focusing on three streams that differed widely in annual stream runoff. These populations appear to have been derived independently, possibly nearly synchronously in geological time, from an ancestral form. Thus, they can be considered statistically independent. Most of the variation in egg size was attributable to differences across the three populations. Although annual and seasonal variation was present, the three populations shifted similarly on both of these time scales. The results support an earlier hypothesis that streamflow, quantified using mean annual runoff, is a strong selective influence on egg size, hence offspring size, favouring larger egg size in populations inhabiting streams with greater levels of runoff.     

A quantitative interpretation of the entry section of the EPPO decision‐support scheme for pest risk analysis

The development of methods to combine components of risk and their associated uncertainty in Pest Risk Analysis (PRA) has received attention in a number of recent European projects. Many of the risk components distinguished in the EPPO Decision‐support scheme (DSS) for PRA are usually difficult to quantify, but when there is detailed knowledge of the pest and pathway, quantification may be possible to a limited extent for the pest entry section of the scheme. The European Food Safety Authority has recently commissioned a project to investigate approaches to quantitative pathway analysis for pests of commodities entering and moving within the EU (QPA‐Food); a sister project concerns non‐food commodities. This paper illustrates the potential for a quantitative pathway model based closely on the Entry Section of the EPPO DSS for PRA, where existing quantitative definitions of rating categories have been used as a basis to estimate the proportion and number of infested lots on a pathway. Such quantification may provide additional insights without requiring substantial changes to the information elicited via the DSS.     

Distribution of herbicide‐resistant acetyl‐coenzyme A carboxylase alleles in Lolium rigidum across grain cropping areas of South Australia

Resistance to the acetyl‐coenzyme A carboxylase (ACCase)‐inhibiting herbicides in Lolium rigidum is widespread in grain cropping areas of South Australia. To better understand the occurrence and spread of resistance to these herbicides and how it has changed with time, the carboxyl transferase (CT) domain of the ACCase gene from resistant L. rigidum plants, collected from both random surveys of the mid‐north of Southern Australia over 10 years as well as stratified surveys in individual fields, was sequenced and target site mutations characterised. Amino acid substitutions occurring as a consequence of these target site mutations, at seven positions in the ACCase gene previously correlated with herbicide resistance, were identified in c. 80% of resistant individuals, indicating target site mutation is a common mechanism of resistance in L. rigidum to this herbicide mode of action. Individuals containing multiple amino acid substitutions (two, and in two cases, three substitutions) were also found. Substitutions at position 2041 occurred at the highest frequency in all years of the large area survey, while substitutions at position 2078 were most common in the single farm analysis. This study has shown that target site mutations leading to amino acid substitutions in ACCase of L. rigidum are widespread across South Australia and that these mutations have likely evolved independently in different locations. The results indicate that seed movement, both within and between fields, may contribute to the spread of resistance in a single field. However, over a large area, the independent appearance and selection of target site mutations conferring resistance through herbicide use is the most important factor.     

Environmental and spatial characterisation of bacterial community composition in soil to inform sampling strategies

Soil physicochemical properties and microbial communities are highly heterogeneous and vary widely over spatial scales, necessitating careful consideration of sampling strategies to provide representative and reproducible soil samples across field sites. To achieve this, the study aimed to establish appropriate sampling methodology and to determine links between the variability of parameters, utilising two sampling strategies. The first (design 1) involved extracting 25 cores from random locations throughout the field and pooling them into five sets of five cores. The second (design 2) involved a further 25 cores within five 1 m² sub-plots. Sub-samples from each sub-plot were pooled in order to determine between and within sub-plot variability. All samples were analysed independently and as pooled sub-samples. Results indicate that pooling spatially separated samples significantly reduced the variability in pH, compared to individual samples. Pooling samples from a small area resulted in lower within sub-plot variability than between sub-plots for pH and bacterial community composition assessed by terminal-restriction fragment length polymorphism analysis. Following multivariate statistical analysis, a large amount of variation in community composition was explained by soil pH, which is remarkable given the relatively small size of the sampling area and minor differences in pH. Moisture content was also important in determining bacterial communities in the random design (design 1). In the 1 m² sub-plot design (design 2), the spatial location of the plots explained a large degree of the variation in bacterial community composition between plots, which was due to spatial autocorrelation of pH and possible additional environmental parameters. This study emphasises the importance of sampling design for obtaining representative samples from soil.     

Scrub-itch mite infestation in the endangered bridled nailtail wallaby

Skin lesions on the ears and inguinal and axillary regions of a number of adult animals within a captive population of the endangered bridled nailtail wallaby ( Onychogalea fraenata ) were associated with the trombiculid mite, Eutrombicula hirsti . The local inflammatory response of these Australian marsupials is described.     

Short-term responses of ground-active beetles to alternative silvicultural systems in the Warra Silvicultural Systems Trial,Tasmania, Australia

The Warra Silvicultural Systems Trial (SST) in Tasmania, Australia provides a framework for investigating the responses of beetles (Order: Coleoptera) to three alternative systems in lowland wet eucalypt forest: aggregated retention; dispersed retention; and understorey islands retained in clearfelled areas. Beetles from three families known to be sensitive to forest management, the families Carabidae (ground-beetles), Curculionidae (weevils) and Leiodidae (fungus-beetles), were collected with pitfall traps prior to harvest, and in the first and third years post-harvest. The retained aggregates in the aggregated retention system maintained beetle assemblages reasonably typical of mature forests, at least in these early years following harvesting. These aggregates appear to provide a stable habitat, with similar species composition in the first and third years post-harvest. In contrast, the harvested areas of the aggregated retention system contained low numbers of beetle species affiliated with mature forest, as did the understorey islands and the dispersed retention system. Relative to clearfelling, all alternative silvicultural systems appeared to be of some benefit to beetles affiliated with mature forest, but aggregated retention retained far greater numbers of these beetles compared to the other systems in Tasmanian wet eucalypt forest.