Dry season habitat use of fishes in an Australian tropical river.

The modification of river flow regimes poses a significant threat to the world's freshwater ecosystems. Northern Australia's freshwater resources, particularly dry season river flows, are being increasingly modified to support human development, potentially threatening aquatic ecosystems and biodiversity, including fish. More information is urgently needed on the ecology of fishes in this region, including their habitat requirements, to support water policy and management to ensure future sustainable development. This study used electrofishing and habitat survey methods to quantify the dry season habitat use of 20 common freshwater fish taxa in the Daly River in Australia's wet-dry tropics. Of twenty measured habitat variables, water depth and velocity were the two most important factors discriminating fish habitat use for the majority of taxa. Four distinct fish habitat guilds were identified, largely classified according to depth, velocity and structural complexity. Ontogenetic shifts in habitat use were also observed in three species. This study highlights the need to maintain dry season river flows that support a diversity of riverine mesohabitats for freshwater fishes. In particular, shallow fast-flowing areas provided critical nursery and refuge habitats for some species, but are vulnerable to water level reductions due to water extraction. By highlighting the importance of a diversity of habitats for fishes, this study assists water managers in future decision making on the ecological risks of water extractions from tropical rivers, and especially the need to maintain dry season low flows to protect the habitats of native fish.

A semi-automated vascular access system for preclinical models.

Murine models are used extensively in biological and translational research. For many of these studies it is necessary to access the vasculature for the injection of biologically active agents. Among the possible methods for accessing the mouse vasculature, tail vein injections are a routine but critical step for many experimental protocols. To perform successful tail vein injections, a high skill set and experience is required, leaving most scientists ill-suited to perform this task. This can lead to a high variability between injections, which can impact experimental results. To allow more scientists to perform tail vein injections and to decrease the variability between injections, a vascular access system (VAS) that semi-automatically inserts a needle into the tail vein of a mouse was developed. The VAS uses near infrared light, image processing techniques, computer controlled motors, and a pressure feedback system to insert the needle and to validate its proper placement within the vein. The VAS was tested by injecting a commonly used radiolabeled probe (FDG) into the tail veins of five mice. These mice were then imaged using micro-positron emission tomography to measure the percentage of the injected probe remaining in the tail. These studies showed that, on average, the VAS leaves 3.4% of the injected probe in the tail. With these preliminary results, the VAS system demonstrates the potential for improving the accuracy of tail vein injections in mice.

Marine-freshwater transitions are associated with the evolution of dietary diversification in terapontid grunters (Teleostei: Terapontidae).

The ecological opportunities associated with transitions across the marine-freshwater interface are regarded as an important catalyst of diversification in a range of aquatic taxa. Here, we examined the role of these major habitat transitions and trophic diversification in a radiation of Australasian fishes using a new molecular phylogeny incorporating 37 Terapontidae species. A combined mitochondrial and nuclear gene analysis yielded a well-supported tree with most nodes resolved. Ancestral terapontids appear to have been euryhaline in habitat affiliation, with a single transition to freshwater environments producing all Australasian freshwater species. Mapping of terapontid feeding modes onto the molecular phylogeny-predicted carnivorous dietary habits was displayed by ancestral terapontids, which subsequently diversified into a range of additional carnivorous, omnivorous, herbivorous and detritivorous dietary modes upon transition to freshwater habitats. Comparative analyses suggested that following the freshwater invasion, the single freshwater clade has exhibited an increased rate of diversification at almost three times the background rate evident across the rest of the family. The marine-freshwater transition within Terapontidae appears to have resulted in substantial dietary radiation in freshwater environments, as well as increased lineage diversification rates relative to euryhaline-marine habitats.

Fish response to the temporal hierarchy of the natural flow regime in the Daly River, northern Australia.

In this study, relationships between flow variation across multiple temporal scales and the distribution and abundance of three fish species, western rainbowfish Melanotaenia australis, sooty grunter Hephaestus fuliginosus and barramundi Lates calcarifer were examined at eight sampling reaches in the Daly River, Northern Territory, Australia. Discharge was highly seasonal during the study period of 2006-2010 with a distinct wet-dry discharge pattern. Significant catchment-wide correlations were identified between species abundance and hydrologic variables across several scales describing the magnitude and variability of flow. A Bayesian hierarchical model which accounted for >80% of variation in abundances for all species and age classes (i.e. juvenile and adult), identified the extent to which the influence of short-term flow variation was dependent upon the historical flow regime. There were distinct ontogenetic differences in these relationships for H. fuliginosus, with variability of recent flows having a negative effect on juveniles which was stronger at locations with higher historical mean daily flow. Lates calcarifer also displayed ontogenetic differences in relationships to flow variation with adults showing a positive association with increase in recent flows and juveniles showing a negative one. The effect of increased magnitude of wet-season flows on M. australis was negative in locations with lower historical mean daily flow but positive in locations with higher historical mean daily flow. The results highlighted how interactions between multiple scales of flow variability influence the abundance of fish species according to their life-history requirements.

Is the elusive Gymnothorax polyuranodon really a freshwater moray?

Analysis of 36 records of the rarely encountered moray Gymnothorax polyuranodon indicate that juveniles and adults inhabit fresh and mildly brackish habitats (salinity < 5) in streams of the Australian Wet Tropics Eighty-one per cent of these records were from freshwater streams and collectively demonstrate that this species inhabits fresh water throughout all seasons. A survey of fish researchers, each with at least 100 h of field experience in Australia's Wet Tropics, revealed that 33% of researchers working in fresh waters (nine of 27 researchers) had encountered the species and 15% of researchers with substantial experience working in estuaries (two of 13 researchers) had encountered the species. The species was not sampled or observed in the nearshore marine environment. The only record of an elver of this species was, however, found in an estuary at a salinity of 33·4. This preliminary evidence suggests adult G. polyuranodon occupy freshwater habitats, but further research is required to understand the complete life cycle, including movements, habitat use and reproductive ecology of the species.

Trophic ecology of northern Australia's terapontids: ontogenetic dietary shifts and feeding classification.

The diets of 21 terapontid species from freshwater environments in northern Australia were investigated to determine the similarity and dissimilarity among species and the extent of any ontogenetic shifts. Distinct ontogenetic dietary shifts occurred in all species for which sufficient data were available, with many species passing through several discrete trophic categories during their life histories. Diets of all juvenile terapontids were similar, mainly comprising aquatic insects and zooplankton. Larger size classes of terapontids diverged into a broad spectrum of feeding groups comprising carnivorous dietary modes (including piscivory and lepidophagy), omnivory (including frugivory and consumption of allochthonous prey), herbivory and detritivory. The results indicate that the terapontids represent Australia's most trophically diverse freshwater fish family.

Performance Characteristics of BGO Detectors for a Low Cost Preclinical PET Scanner.

PETbox is a low-cost benchtop PET scanner dedicated to high throughput preclinical imaging that is currently under development at our institute. This paper presents the design and characterization of the detectors that are used in the PETbox system. In this work, bismuth germanate scintillator was used for the detector, taking advantage of its high stopping power, high photoelectric event fraction, lack of intrinsic background radiation and low cost. The detector block was segmented into a pixelated array consisting of 20 × 44 elements, with a crystal pitch of 2.2 mm and a crystal cross section of 2 mm × 2 mm. The effective area of the array was 44 mm × 96.8 mm. The array was coupled to two Hamamatsu H8500 position sensitive photomultiplier tubes, forming a flat-panel type detector head with a sensitive area large enough to cover the whole body of a typical laboratory mouse. Two such detector heads were constructed and their performance was characterized. For one detector head, the energy resolution ranged from 16.1% to 38.5% full width at half maximum (FWHM), with a mean of 20.1%; for the other detector head, the energy resolution ranged from 15.5% to 42.7% FWHM, with a mean of 19.6%. The intrinsic spatial resolution was measured to range from 1.55 mm to 2.39 mm FWHM along the detector short axis and from 1.48 mm to 2.33 mm FWHM along the detector long axis, with an average of 1.78 mm. Coincidence timing resolution for the detector pair was measured to be 4.1 ns FWHM. These measurement results show that the detectors are suitable for our specific application.

Widespread omnivory and low temporal and spatial variation in the diet of fishes in a hydrologically variable northern Australian river.

This article examines the trophic ecology of freshwater fishes (22 species in 15 families) in a wet and dry tropical Australian river of high intra-annual and interannual hydrological variability. Seven major trophic groups were identified by cluster analysis; however, four food items (filamentous algae, chironomid larvae, Trichoptera larvae and Ephemeroptera nymphs) comprised almost half of the average diet of all species. The influence of species, fish size, spatial effects and temporal effects on food use was investigated using redundancy analysis. Size, time and space accounted for little of the perceived variation. Ontogenetic changes in diet were minor and limited to a few large species. Spatial variation in trophic composition of the fish assemblages reflected the effects of the Burdekin Falls and dam, a major geographic barrier, on species distributions. Little spatial variation in diet was detected after accounting for this biogeographical effect. Temporal variations in flow, although marked, had little effect on variations in fish diet composition due to the low temporal diversity of food resources in physically monotonous sand and gravel channels. Species identity accounted for<50% of the observed variation in food choice; omnivory and generalism were pronounced. The aquatic food web of the Burdekin River appears simple, supported largely by autochthonous production (filamentous and benthic microalgae, and to some extent, aquatic macrophytes). Allochthonous food resources appear to be unimportant. The generalist feeding strategies, widespread omnivory and absence of pronounced trophic segregation reported here for Burdekin River fishes may be common to variable and intermittent rivers of subtropical and tropical northern Australia with similar fish communities and may be a general feature of rivers of low habitat diversity and characterized by flow regimes that vary greatly both within and between years.

The effects of a chronic application of chlorpyrifos on the macroinvertebrate fauna in an outdoor artificial stream system: species responses.

An outdoor artificial stream system was used to examine the effects of a chronic application of the organophosphate pesticide chlorpyrifos on the invertebrate fauna of the system. Two replicate streams received chlorpyrifos for 21 days at the high dose (5 micrograms.liter-1) or low dose (0.1 microgram.liter-1) or only the carrier solution with which chlorpyrifos is mixed for commercial sale (1,1,1-trichloroethane and xylene). Streams behaved as replicates with respect to five water quality parameters. Seventy-four nonchironomid and 24 chironomid taxa were recorded during the study. The number of taxa and total invertebrate abundance were significantly reduced by both high and low doses of the pesticide. Shannon-Weaver diversity was also reduced by both high and low doses of the pesticide whereas evenness increased in high dose streams. The individual abundances of 9/36 nonchironomid and 13/19 chironomid taxa were significantly reduced by pesticide application; the abundance of one taxon, the gastropod Physastra, increased. The biomass of periphyton in the streams was affected by changes in the abundance of chironomid grazers and Physastra, and the slow recovery of grazers from mortality due to chlorpyrifos appeared to result in a higher biomass of periphyton in the high dose streams than in controls and low dose streams 21 days after dosing ceased. Inverse relationships between the amounts of fine particulate organic matter (FPOM) and the sum of the numbers of all taxa of collector-gatherers (as well as numbers of four individual taxa) were interpreted as disruption of the processing of FPOM by members of this trophic group following toxic effects of chlorpyrifos. The implications of the study for biological monitoring of the direct and indirect effects of chronic doses of chlorpyrifos on streams are discussed, and the use of chironomid larvae and periphyton in biomonitoring to detect pesticide impacts is particularly recommended.

The effects of a pulsed application of chlorpyrifos on macroinvertebrate communities in an outdoor artificial stream system.

The results of an experiment examining the effects of pulsed application of a pesticide, chlorpyrifos, in an outdoor replicated artificial stream system are described. Two levels of chlorpyrifos were used, 0.1 microgram.liter-1 (low dose) and 5.0 micrograms.liter-1 (high dose), and applied for 6 hr. Low-dose streams showed little impact from the treatment and were indistinguishable from control streams. Significant reductions in invertebrate density occurred in the high-dose streams and were mainly due to reductions in density of chironomid larvae. There were no significant reductions in taxon richness associated with the treatments indicating no localized extinctions of species. Diversity measures were insensitive to the changes observed in the streams. Ordination and classification procedures were more illuminating and indicated that the major effect of pesticide application was to interfere with the normal pattern of community change occurring within the system. Recovery following treatment was rapid. The results are discussed with reference to the use of indicator species and biological monitoring strategies intended to identify human-mediated disturbance.

An outdoor replicated artificial stream system: design, operating conditions, and initial invertebrate colonization.

The design and operating conditions of an outdoor replicated stream system are described. The facility is composed of a long inlet stream, a header weir which diverts inflowing water to six artificial stream channels (each 45 m long and 40 cm wide), a settlement pond at the end of the channels, and an outlet stream which diverts the water back to an irrigation channel. Flow regulation is achieved by "V-notched" gates at the head of each stream and depth by a second set of gates at the end of each stream. Physicochemical conditions were monitored over a 260-day period and even though significant temporal variation was detected, little between-stream variation was observed for most parameters. Small, but significant, between-stream differences in dissolved oxygen and pH were detected but were attributed to sampling procedure rather than real between-stream differences. A relatively rich invertebrate fauna colonized the streams. Invertebrate densities increased rapidly after initiation of flow and stabilized after 38 days. Chironomoid midge larvae were numerically the most important taxa, although the proportion of total density contributed by this group changed significantly with time. Taxon richness, chironomid taxon richness, diversity, and eveness also increased with time until a stable point was reached after 90 days of flow. No significant between-stream difference in any of these parameters was detected suggesting that colonization dynamics were similar in each stream.