Spatially structured relationships between white banana prawn (Penaeus merguiensis) catch and riverine flow in the Northern Prawn Fishery, Australia

Water resource development can lead to the significant alteration of natural flow regimes, which can have impacts on the many aquatic species that rely on both freshwater and estuarine environments to successfully complete their lifecycles. In tropical northern Australia, annual catches of commercially harvested white banana prawns (WBP) are highly variable in response to environmental conditions, namely rainfall and subsequent riverine flow. However, little is known about the spatial extent to which flow from individual rivers influences offshore WBP catch. In this study, we quantify how the relationship between WBP catch in the Gulf of Carpentaria is influenced by flow from the Mitchell River, Queensland Australia. We used a Bayesian framework to model both prawn presence and catch per unit effort, and found evidence that multiple components of the flow regime contribute to fishery catch. We also found evidence to suggest that the relationships between prawn presence and flow were spatially structured across the fishing ground. Our results suggest that attributing fishery catch to a single river remains challenging, though highlights the importance of maintaining natural flow regimes to support a highly valuable commercial fishery species in the face of potential water resource development.

Assessing climate change impacts on wetlands in a flow regulated catchment: A case study in the Macquarie Marshes, Australia

Globally wetlands are increasingly under threat due to changes in water regimes as a result of river regulation and climate change. We developed the Exploring CLimAte Impacts on Management (EXCLAIM) decision support system (DSS), which simulates flow-driven habitat condition for 16 vegetation species, 13 waterbird species and 4 fish groups in the Macquarie catchment, Australia. The EXCLAIM DSS estimates impacts to habitat condition, considering scenarios of climate change and water management. The model framework underlying the DSS is a probabilistic Bayesian network, and this approach was chosen to explicitly represent uncertainties in climate change scenarios and predicted ecological outcomes. The results suggest that the scenario with no climate change and no water resource development (i.e. flow condition without dams, weirs or water license entitlements, often regarded as a surrogate for 'natural' flow) consistently has the most beneficial outcomes for vegetation, waterbird and native fish. The 2030 dry climate change scenario delivers the poorest ecological outcomes overall, whereas the 2030 wet climate change scenario has beneficial outcomes for waterbird breeding, but delivers poor outcomes for river red gum and black box woodlands, and fish that prefer river channels as habitats. A formal evaluation of the waterbird breeding model showed that higher numbers of observed nest counts are typically associated with higher modelled average breeding habitat conditions. The EXCLAIM DSS provides a generic framework to link hydrology and ecological habitats for a large number of species, based on best available knowledge of their flood requirements. It is a starting point towards developing an integrated tool for assessing climate change impacts on wetland ecosystems.

Bayesian Networks as a screening tool for exposure assessment

A tiered approach to contamination exposure assessment is currently adopted in many countries. Increasing the site-specific information in exposure assessments is generally recommended when guideline values for contaminants in soil are exceeded. This work details a Bayesian Network (BN) approach to developing a site-specific environmental exposure assessment that focuses on the simple mapping and assessment of assumptions and the effect of new data on assessment outcomes. The BN approach was applied to a floodplain system in New South Wales, Australia, where site-specific information about elevated antimony (Sb) concentrations and distribution in soils was available. Guidelines for exposure assessment in Australia are used as a template for this site, although the approach is generic. The BN-based assessment used an iterative approach starting with limited soil Sb data (41 samples ranging from 0 to 18 mg kg-(1) Sb) and extending the model with more detailed Sb data (145 samples ranging from 0 to 40 mg kg-(1) Sb). The analyses identified dominant exposure pathways and assessed the sensitivity of these pathways to changes in assumptions and the level of site-specific information available. In particular, there was a 10.8% probability of exceeding the tolerable daily intake of Sb in the case study when the limited soil Sb data was used, which increased to 26.2% with the more detailed sampling regime. There was also a 47% decrease in the probability of overexposure to Sb when the dermal bioavailability of arsenic (a similar metalloid) was used as a surrogate measure instead of a default bioavailability of 100%. We conclude that the BN approach to soil exposure assessment has merit both in the context of Australian and international soil exposure assessments.

Physiological changes in reproductively active rainbowfish (Melanotaenia fluviatilis) following exposure to naphthalene

Naphthalene makes up a substantial fraction of polycyclic aromatic hydrocarbons (PAHs) in crude oil and is an important by-product of industry; however, few studies have investigated the toxicity of naphthalene to aquatic organisms. We examined the toxicity of increasing concentrations (0, carrier control, 130, 200 and 400microg/l) of naphthalene to adult rainbowfish (Melanotaenia fluviatilis) for 3 and 14 days to determine its potential to act as an endocrine disruptor. After exposure for 3 days, no changes in sex steroids were measured. After 14 days, a decrease of serum estradiol in females and an increase in serum testosterone in males was observed. These results suggest that naphthalene has the potential to act as an endocrine disruptor, although since no changes in plasma vitellogenin concentrations were observed in either sex, it is unlikely that naphthalene is acting as a xenoestrogen. There was a positive correlation between the incidences of deformities in larval offspring with increasing naphthalene concentrations, suggesting parental transfer of the toxicant. Egg production, hatchability and larval lengths remained unaltered, whilst few changes were measured in gamma-glutamyltranspeptidase (GTP), an enzymatic indicator of spermatogenesis. Contrary to other PAHs, hepatic ethoxyresorufin-O-deethylase (EROD) activities declined with increasing exposure concentration, suggesting that naphthalene was either having a cytotoxic effect or disrupting enzyme synthesis.

Toxicity of water and sediment from stormwater retarding basins to Hydra hexactinella

Hydra hexactinella was used to assess the toxicity of stormwater and sediment samples from three retarding basins in Melbourne, Australia, using an acute test, a sublethal test, and a pulse test. Stormwater from the Avoca St retarding basins resulted in a LC50 of 613 ml/L, NOEC and LOEC values of 50 ml/L and 100 ml/L, while the 7h pulse exposure caused a significant increase in the mean population growth rate compared to the control. Water samples from the two other retarding basins were found non-toxic to H. hexactinella. This is the first study to employ sediment tests with Hydra spp. on stormwater sediments and a lower population growth rate was observed for organisms exposed to sediment from the Avoca St retarding basins. The behavioral study showed that H. hexactinella tended to avoid the sediment-water interface when exposed to sediment from all retarding basins, compared to the reference sediment. Further work is needed to determine the long-term effects of stormwater polluted sediments and acute effects due to organism exposure to short-term high concentrations during rain events.

Use of the Australian crimson-spotted rainbowfish (Melanotaenia fluviatilis) as a model test species for investigating the effects of endocrine disruptors

Few studies have investigated the potential reproductive effects of toxicants on Australian freshwater fish species. The present study uses the Australian rainbowfish (Melanotaenia fluviatilis) as a model for testing the potential effects of 17beta-estradiol. Groups of reproductively active rainbowfish were exposed to waterborne 17beta-estradiol (control, carrier control, and 30, 100, 300, and 1,000 ng/L) for 3- and 14-d periods. Biomarkers of both low ecological relevance (plasma estradiol and testosterone, phosphoprotein, gamma-glutamyltranspeptidase [GTP]) and high ecological relevance (egg counts, hatchability, larval lengths, histopathology) were measured and the relationships between these examined. Relative to the controls, exposed female rainbowfish had a decline in plasma estradiol. An increase in phosphoprotein (vitellogenin) also was observed after exposure to 1,000 ng/L after 3 d, and histological examination of the gonads showed an increase in oocyte atresia at 1,000 ng/L on days 3 and 14. Changes in egg production were observed at 300 and 1,000 ng/L. No changes were detected to egg hatchability and larval lengths of offspring. Although there were no changes in male rainbowfish plasma testosterone or the histological organization of testes, levels of phosphoprotein increased and GTP activities were increased after 3 d of exposure at all test concentrations, but these declined at day 14. The present study demonstrated that, though measurements at the biochemical level were responsive to 17beta-estradiol exposure, fewer changes were observed in markers of higher ecological relevance at the exposures concentrations and durations tested.

Cytological changes in association with ethoxyresorufin o-deethylase induction in fish upon dietary exposure to benzo[a]pyrene

Juvenile areolated grouper (Epinephelus areolatus) were exposed to two levels of dietary benzo[a]pyrene (BaP; 0.25-12.5 microg/g body wt/d) for four weeks, followed by four weeks of depuration. Significant increase in hepatic ethoxyresorufin O-deethylase (EROD) activities was found after one week, preceding an increase in lipopigments (as measured by quantitative transmission electron microscopy) in week 2 of exposure. The EROD activities in the BaP-treated fish subsided at week 4 of exposure and throughout the depuration period. Lipopigments in the high-dose group appeared to be more persistent than that of the EROD activity during the exposure period and remained significantly higher than that of the controls at week 4. Levels of lipopigments, however, rapidly subsided on withdrawal of BaP exposure. These results appear to suggest that changes in EROD activities would precede cytological changes and that both the observed cytological and biochemical changes are reversible. Results of the present study also lend further support to our earlier findings on Solea ovata, that a significant relationship exists between EROD activity and lipopigment accumulation (as measured by volume density, absolute volume, numerical density, and absolute density; r = 0.483-0.358, p < 0.05), regardless of fish species (S. ovata and aerolated grouper) as well as the routes of exposure to BaP (intraperitoneal injection or dietary exposure). This provides strong supporting evidence that elevated EROD activities in fish liver do not merely indicate exposure to polyaromatic hydrocarbons (PAHs) but are also associated with significant biological effects. Our results showed that hepatic EROD activity and lipopigments could be used to indicate recent exposure of the fish to BaP/PAHs.

Evaluation of biomarkers of exposure and effect in juvenile areolated grouper (Epinephelus areolatus) on foodborne exposure to benzo[a]pyrene

Food-borne benzo[a]pyrene (B[a]P) was administered daily to juvenile grouper (Epinephelus areolatus) at two environmentally realistic concentrations (a low dose of 0.25 microg B[a]P/g body wt/d and a high dose of 12.5 microg B[a]P/g body wt/d) to investigate and relate temporal changes in body burden of B[a]P, hepatic ethoxyresorufin-O-deethylase (EROD) activities, growth, RNA:DNA ratio, estradiol, testosterone, and triiodothyronine (T3). After feeding with B[a]P diets for four weeks, fish were fed with normal diet for another four weeks to study recovery of the various biomarkers during the depuration period. After one week of exposure, both body muscle B[a]P burdens and hepatic EROD activities significantly increased. Body burdens were stable in tissues until the fourth week of exposure, when concentrations in the high-dose group increased markedly, at which time a concomitant decrease in EROD was found. During the depuration period, body burdens decreased in the second week, and EROD declined in the first week. Growth and RNA:DNA ratio were unaltered. Despite large variations found in sex steroid levels, elevation of testosterone was clearly evident in the fourth week, showing that B[a]P may disrupt the balance of sex steroids in fish. Significantly, increases in plasma-free T3 concentrations were found in the fourth week of exposure and the first week of depuration, suggesting that development and reproduction may potentially be at risk during chronic exposures. Our data also suggest that these hormonal disturbances are not persistent and that normal hormonal levels can be restored soon after contamination is abated.

Hydrocarbon-induced changes to metabolic and detoxification enzymes of the Australian crimson-spotted rainbowfish (Melanotaenia fluviatilis)

The toxicity of petroleum hydrocarbons to marine aquatic organisms has been widely investigated; however, the effects on freshwater environments have largely been ignored. Selected biomarkers were measured in a freshwater species, the crimson-spotted rainbowfish (Melanotaenia fluviatilis). Fish were exposed to either a water-accommodated fraction (WAF) of crude oil or a dispersed crude oil water-accommodated fraction (DCWAF) for 3 days and were depurated for 14 days. Generally, biomarkers were altered following the short-term exposures but recovered after 14 days of depuration. Metabolic enzymes measured in gill tissue were citrate synthase and lactate dehydrogenase (LDH). As a result of WAF and DCWAF exposures, citrate synthase and LDH activities increased. Enzyme activities returned to control levels following depuration. Subsequent to the WAF exposure, hepatic ethoxyresorufin-O-deethylase (EROD) activity levels were higher than controls and they returned to control levels during depuration. For the DCWAF exposure, EROD was induced by a TPH (total petroleum hydrocarbons) concentration of 14.5 mg/L; however, after depuration the 14.5 mg/L TPH group had lower EROD activity than did controls. There were no changes in liver- to body-weight ratios or the histopathological organization of gill or liver tissues. As the majority of biomarkers returned to control levels after 14 days of depuration, rainbowfish were able to recover from short-term exposures to crude oil and dispersed crude oil.

Toxicity testing of crude oil and related compounds using early life stages of the crimson-spotted rainbowfish (Melanotaenia fluviatilis)

The toxicity of petroleum hydrocarbons to marine aquatic organisms has been widely investigated; however, the effects on freshwater environments have largely been ignored. In the Australian freshwater environment, the potential impacts of petroleum hydrocarbons are virtually unknown. The toxicity of crude oil and related compounds were measured in the sensitive early life stages of the crimson-spotted rainbowfish (Melanotaenia fluviatilis). Waterborne petroleum hydrocarbons crossed the chorion of embryonic rainbowfish, reducing survival and hatchability. Acute exposures resulted in developmental abnormalities at and above 0.5 mg/L total petroleum hydrocarbons (TPH). Deformities included pericardial edema, disturbed axis formation, and abnormal jaw development. When assessing the acute toxicities of the water-accommodated fraction (WAF) of crude oil, dispersants, dispersant-oil mixtures, and naphthalene to larval rainbowfish, the lowest to highest 96-h median lethal concentrations for day of hatch larvae were naphthalene (0.51 mg/L), dispersed crude oil WAF (DCWAF)-9527 (0.74 mg/L TPH), WAF (1.28 mg/L TPH), DCWAF-9500 (1.37 mg/L TPH), Corexit 9500 (14.5 mg/L TPH), and Corexit 9527 (20.1 mg/L). Using naphthalene as a reference toxicant, no differences were found between the sensitivities of larval rainbowfish collected from adults exposed to petroleum hydrocarbons during embryonic development and those collected from unexposed adults.

Reproductive potential of crimson-spotted rainbowfish (Melanotaenia fluviatilis) following short-term exposure to bass strait crude oil and dispersed crude oil

An examination of the potential of crude oil and mixtures of dispersants and crude oil to act as reproductive toxicants is reported in this article. The short-term effects of a water-accommodated fraction of crude oil (WAF) and a dispersed crude oil water-accommodated fraction (DCWAF) on selected reproductive end points were measured by conducting 3-day exposures to the crimson-spotted rainbowfish (Melanotaenia fluviatilis). Exposures were followed by 14-day depuration periods to determine the ability of fish to recover from the exposure. There were no changes to egg production, hatchability, or larval lengths for the WAF and DCWAF test periods. There were no changes to plasma estradiol or testosterone concentrations, gonadosomatic indices, or histopathological organization of gonad tissues after the exposure and depuration periods for both WAF and DCWAF. As reproductive parameters were not altered after 3 days of exposure and 14 days of depuration, crimson-spotted rainbowfish were able to endure short-term exposures to crude oil and dispersed crude oil.

Potential of two hydra species as standard toxicity test animals

The potential for using pink hydra (Hydra vulgaris) and green hydra (Hydra viridissima) as a model invertebrate for the toxicity testing of xenobiotics was investigated. Test compounds were 4-chlorophenol, endosulfan, and copper. The reference toxicant 4-chlorophenol was used as a standard during toxicity testing to ensure the sensitivity of hydra did not change over time. Hydra had a low sensitivity to 4-chlorophenol and endosulfan compared to other freshwater species. The 96-h LC50 (SE) values for 4-chlorophenol and endosulfan were 32 mg/L (1.3) and 0.81 mg/L (0.1), respectively, for pink hydra, and 45 mg/L (6.1) and 0.67 mg/L (0.02), respectively, for green hydra. Based on population growth rates, the 6-day NOEC and LOEC results for pink hydra exposed to 4-chlorophenol and endosulfan were <1.1 and 1.1 mg/L, and 0.044 microg/L and 0.080 mg/L, respectively; results for green hydra were 10.3 and 22.3 mg/L, and 0.060 and 0.080 mg/L, respectively. Following exposure to copper, the 96-h LC50 (SE) values were 26 microg/L (3.4) for pink hydra and 8.5 microg/L (0.3) for green hydra, respectively. Based on population growth rates, the 7-day population growth NOEC and LOEC values for both pink and green hydra exposed to copper were 4 and 8 microg/L, respectively. Results indicate that hydra have the potential for use in acute and subchronic toxicity testing of inorganic toxicants, but have a low sensitivity to organic toxicants.

Evaluation of low cost in-line milk samplers for estimating individual cow somatic cell counts

The Dairy Herd Improvement Fund of Victoria recently identified a requirement for a simple and inexpensive in-line sampler to enable dairy farmers to collect representative milk samples for counting somatic cells. We found that the currently available simple in-line milk samplers, when connected to standard 35 ml collection vessels, terminate sampling early in a milking, and thus provide samples that are unrepresentative of the whole milking. We showed that cell count during a milking varies greatly, tending to be high for the first 1-21. Analyses of resulting samples will thus tend to overestimate cell counts if samplers are used in their traditional way. We found greater sampling rates in high-line compared with low-line milking systems, and consequently developed modified samplers suitable for both situations. Our samplers utilize low sampling rates (approximately 1-3%) and large collection vessels (450 ml). Compared with currently available simple in-line samplers, our type of sampler provided milk samples considerably more representative of the entire milking for the majority of cows. In conjunction with subsampling, they provided samples of appropriate size (12.5 ml minimum to 25 ml maximum) for testing fat, protein, lactose and cell count. Cell count results indicated that errors associated with the use of currently available simple in-line samplers could frequently be > 200%. In contrast, we found that use of our samplers gave an estimate for cell count that was only slightly higher (mean 20%) than that from samples collected by an approved Tru-Test sampler.