Australian Fish Research Articles

Barriers to hybridisation and their conservation implications for a highly threatened Australian fish species

AbstractHybridisation and introgression are natural phenomena that may lead to the transfer of adaptive alleles from one species to another and increased species diversity. At the same time, hybridisation and subsequent introgression threaten many species world‐wide through the loss of genetic and species diversity. In Australia, introgressive hybridisation between native and alien species has not typically been considered a significant threat to native biodiversity because of the taxonomic distance between native and alien biota. However, many native fish have been introduced outside their natural range. Recently, four taxa in the genus Melanotaenia have been nationally listed as threatened due to introgressive hybridisation with introduced Melanotaenia splendida. We examined pre‐ and post‐zygotic barriers to hybridisation between M. splendida and one of these threatened taxa—Running River rainbowfish (RRR)—to assess the potential for hybridisation to occur. We used dichotomous mate choice experiments to examine pre‐zygotic barriers and mating experiments to examine post‐zygotic barriers. Size was not a significant predictor of the proportion of time subjects spent with a potential mate, nor was there any significant difference in the amount of time subjects spent with potential mates of their own or the opposite species. Eggs from hybrid pairings with female RRR had a slightly higher hatching rate than those from hybrid pairings with female M. splendida, but neither were significantly different from intraspecies crosses. We could not identify any definite barriers to hybridisation, demonstrating that the introduction of “native” fish species outside their natural range poses a higher risk of hybridisation than previously thought. We call for better education around the consequences of moving “native” fish and the development of rapid response plans to deal with recently established alien populations of Australian fish species in order to prevent future extinctions due to introgressive hybridisation.

The South American and Australian percichthyids and perciliids. What is new about them?

ABSTRACT A study including morphological characters and mitogenomics of South American and Australian fishes previously assigned to Percichthyidae was conducted. Results generated from these different data sets reveal major disagreements concerning the content and interpretation of the so-called percichthyids. A phylogenetic analysis based on 54 morphological characters suggests the existence of two major clades: (1) Percichthyidae, including the South American Percichthys and the Australian taxa Macquaria australasica, Macquaria (= Plectroplites), and Maccullochella; (2) Perciliidae with the South American genus Percilia at the base plus more advanced Australian genera Nannoperca, Nannatherina, Bostockia, and Gadopsis. In contrast, molecular and mitogenomic evidence suggests only one clade (Percichthyidae), with the exclusion of species of Macquaria (= Percalates). Additionally, the results reveal the existence of various taxonomic problems, such as the current interpretation of only one species of Percichthys in Argentina, an interpretation that is not supported by the present study; the existence of cryptic species of Percilia as well as of Gadopsis, Nannoperca, and Macquaria that will increase the diversity of the genera; and the need for an extensive revision of species previously assigned to Percalates versus Macquaria. Disagreements point to the need to develop further research on the so-called percichthyids and perciliids.

Assessment of genetic structure among Australian east coast populations of snapper Chrysophrys auratus (Sparidae)

Snapper Chrysophrys auratus is a high-value food fish in Australia targeted by both commercial and recreational fisheries. Along the east coast of Australia, fisheries are managed under four state jurisdictions (Queensland, Qld; New South Wales, NSW; Victoria, Vic.; and Tasmania, Tas.), each applying different regulations, although it is thought that the fisheries target the same biological stock. An allozyme-based study in the mid-1990s identified a weak genetic disjunction north of Sydney (NSW) questioning the single-stock hypothesis. This study, focused on east-coast C. auratus, used nine microsatellite markers to assess the validity of the allozyme break and investigated whether genetic structure exists further south. Nine locations were sampled spanning four states and over 2000km, including sites north and south of the proposed allozyme disjunction. Analyses confirmed the presence of two distinct biological stocks along the east coast, with a region of genetic overlap around Eden in southern NSW, ~400km south of the allozyme disjunction. The findings indicate that C. auratus off Vic. and Tas. are distinct from those in Qld and NSW. For the purpose of stock assessment and management, the results indicate that Qld and NSW fisheries are targeting a single biological stock.A

Control of Globally Invasive Common Carp: An 11‐Year Commercial Trial of the Williams’ Cage

AbstractThe Common Carp Cyprinus carpio is a major pest fish in Australia, North America, New Zealand, and parts of Europe. The Williams’ carp separation cage was developed to separate Common Carp from native fish as they pass through fishways by exploiting their strong migratory and unique jumping behaviors. We report on an 11‐year commercial application of the Williams’ cage at Lock 1 on the lower Murray River (southeast Australia), where a high biomass of Common Carp resides. Between November 2007 and January 2018, the cage was operated by a collaborative team of river managers, weir keepers, commercial fishers, and researchers. To date, approximately 723 metric tons of adult Common Carp (~289,431 fish) have been captured at a maximum rate of 5 metric tons/d. These fish were marketed for a total return of over AU$0.90 million, far exceeding setup costs. Catches and separation efficiencies were highest in austral spring, when fish were migrating to spawn, and bycatch of nontarget native fish was practically zero (0.03%). Population modeling indicated that a combination of commercial carp fishing, low inflows, and the Williams’ cage has caused a significant reduction in Common Carp numbers in the lower Murray River. The Williams’ cage has now successfully moved from an experimental idea to full commercial viability, and at Lock 1 it is playing a valuable role in controlling the dispersal and abundance of globally invasive Common Carp.

Fresh eyes on an old issue: Demand-side barriers to a discard problem

Discarding is a worldwide problem in small-scale and industrial fisheries alike. A significant proportion of discarded fish are edible, and if high post-release mortality occurs, the practice may seem wasteful in the context of food security. There are different reasons for discarding which can be related to demand-side issues (e.g. market preferences), supply-side issues (e.g. on-board storage capacity), and management regulations (e.g. size limits). We carried out analyses to determine why discarding was occurring in a trawl fishery operating in southern Australia’s Great Australian Bight. Currently up to 56% of the fishery catch may be discarded – of which a considerable portion are edible species. The economic viability of the fishery was also considered by revenue from both target species and bycatch species based on a typical vessel. Our research found there are no supply-side barriers and that discarding in this fishery is driven by demand-side barriers. Without addressing demand-side issues for discards, our economic analysis shows that this fishery may be economically challenged and in the broader context, this issue may compromise the long-term supply of fresh Australian fish. Much of the focus to deal with fisheries discards has been directed at the catch sector through development of technical modifications of the fishing gear. However, to help address the discard issue it is important that all supply chain participants, including consumers, understand and contribute to solutions. Our results suggest that if more emphasis was placed on the market and consumer end of the seafood supply chain, the discard problem could be better addressed. We suggest a range of initiatives from government, industry, NGOs and seafood consumers. Technical and industry-led approaches such as sustainability through programs and certification requiring fisheries to meet standards is only part of the story. Consumer awareness regarding their role in creating sustainable fisheries and sustaining locally important fisheries can be enhanced by selecting a wider choice of seafood for consumption.

Utilising the boundary layer to help restore the connectivity of fish habitats and populations

Culverts are a major cause of habitat fragmentation in freshwater ecosystems, are a barrier to fish movement, and can be regarded as a significant contributor in the decline of freshwater fish populations globally. To try to address this, various culvert remediation designs have been implemented, including the installation of vertical baffles and the provision of naturalistic (rock) substrates. While remediation strategies generally aim to reduce the velocity of water flowing through the structure, there is often resistance to their use because the resultant reduction in culvert discharge can negatively impact upstream flooding while also resulting in debris clogging and increased culvert maintenance costs. In addition, baffles markedly increase water turbulence that may be detrimental to passage by some fish species or size classes. Here we present some novel remediation designs that exploit the reduced water velocity in boundary layers along the culvert wall to enhance fish passage without significantly compromising discharge capacity. These longitudinal designs produce an expanded reduced velocity zone along the culvert margins that generate minimal turbulence. We show that these novel designs are significantly advantageous to the swimming endurance and traversability for six small-bodied Australian fish species. We also provide data on how and why some culvert baffle designs may impede small-bodied fish passage. This data scales with increasing water velocity, encompassing inter-specific differences in swimming capacity. These results have broad implications for the movement of small-bodied fish species, and the successful recruitment of large-bodied commercially important species, where baffles have been implemented.

Utilizing individual fish biomass and relative abundance models to map environmental niche associations of adult and juvenile targeted fishes

Many fishes undergo ontogenetic habitat shifts to meet their energy and resource needs as they grow. Habitat resource partitioning and patterns of habitat connectivity between conspecific fishes at different life-history stages is a significant knowledge gap. Species distribution models were used to examine patterns in the relative abundance, individual biomass estimates and environmental niche associations of different life stages of three iconic West Australian fishes. Continuous predictive maps describing the spatial distribution of abundance and individual biomass of the study species were created as well predictive hotspot maps that identify possible areas for aggregation of individuals of similar life stages of multiple species (i.e. spawning grounds, fisheries refugia or nursery areas). The models and maps indicate that processes driving the abundance patterns could be different from the body size associated demographic processes throughout an individual’s life cycle. Incorporating life-history in the spatially explicit management plans can ensure that critical habitat of the vulnerable stages (e.g. juvenile fish, spawning stock) is included within proposed protected areas and can enhance connectivity between various functional areas (e.g. nursery areas and adult populations) which, in turn, can improve the abundance of targeted species as well as other fish species relying on healthy ecosystem functioning.

Transport pathways shape the biogeography of alien freshwater fishes in Australia

AbstractAimChanging preferences regarding which species humans have transported to new regions can have major consequences for the potential distribution of alien taxa, but the mechanisms shaping these patterns are poorly understood. We assessed the extent to which changes in human preferences for transporting and introducing alien freshwater fishes have altered their biogeography.LocationAustralia.MethodsWe compiled an up‐to‐date database of alien freshwater fishes established in drainages in Australia before and after the number of established alien fish species doubled (pre‐1970 and post‐1970, respectively). Using metacommunity models, we analysed the influence of species traits and drainage features on the distribution of alien fishes that established pre‐ and post‐1970.ResultsAlien fishes in Australia were introduced via four main transport pathways: acclimatization, aquaculture, biocontrol and ornamental trade. The relative importance of each pathway changed substantially between the two periods, accompanied by changes in the distribution of alien fishes and the variables predicting their distribution. Pre‐1970, most species (64%) were introduced by acclimatization societies for purposes such as angling and biocontrol, and these fish have established in inland drainages more heavily impacted by human activities. In contrast, most of the post‐1970 introductions (69%) were ornamental fishes, with most species established in small, north‐eastern, tropical and subtropical coastal drainages.Main conclusionsSubstantial changes in introduction preferences and transport pathways over time have altered both the patterns and underlying processes shaping the biogeography of alien fishes in Australia. Our findings highlight the need for caution when using historical data to infer potential future distributions of alien species. The continuing spread of alien species means traditional biogeographical units may no longer be identifiable in the foreseeable future.

Three new species of Prosorhynchoides (Digenea: Bucephalidae) from Tylosurus gavialoides (Belonidae) in Moreton Bay, Queensland, Australia

We surveyed 30 individuals of Tylosurus gavialoides (Castelnau) (Belonidae) collected from Moreton Bay, Queensland, Australia, and describe three new species of Prosorhynchoides Dollfus, 1929 from them. The new species are morphologically distinct from existing Prosorhynchoides spp. and 28S and ITS-2 ribosomal DNA data further supports our morphological findings. We also conduct the first mitochondrial DNA analysis of species of Prosorhynchoides. The new species from T. gavialoides form a strongly supported clade on the basis of the two ribosomal markers, further supporting the emerging hypothesis that bucephaline clades are strongly associated with host groups. We have not observed any of the new species reported here in over 3500 surveyed individuals of other piscivorous fish in Australia, suggesting that these species are host-specific at least to belonids, if not to only T. gavialoides. Our findings support previous reports that suggest that belonids are exceptional hosts for bucephalids. We predict that further sampling of the numerous other belonid species present in Australian waters, for which nothing is known of the bucephalid fauna, will uncover further bucephalid richness.

Photo-induced toxicity following exposure to crude oil and ultraviolet radiation in 2 Australian fishes.

Some polycyclic aromatic hydrocarbons (PAHs), components of crude oil, are known to cause increased toxicity when organisms are co-exposed with ultraviolet radiation, resulting in photo-induced toxicity. The photodynamic characteristics of some PAHs are of particular concern to places like Australia with high ultraviolet radiation levels. The objective of the present study was to characterize the photo-induced toxicity of an Australian North West Shelf oil to early life stage yellowtail kingfish (Seriola lalandi) and black bream (Acanthopagrus butcheri). The fish were exposed to high-energy water accommodated fractions for 24 to 36 h. During the exposure, the fish were either co-exposed to full-intensity or filtered natural sunlight and then transferred to clean water. At 48 h, survival, cardiac effects, and spinal deformities were assessed. Yellowtail kingfish embryos co-exposed to oil and full-spectrum sunlight exhibited decreased hatching success and a higher incidence of cardiac arrhythmias, compared with filtered sunlight. A significant increase in the incidence of pericardial edema occurred in black bream embryos co-exposed to full-spectrum sunlight. These results highlight the need for more studies investigating the effects of PAHs and photo-induced toxicity under environmental conditions relevant to Australia. Environ Toxicol Chem 2018;37:1359-1366. © 2018 SETAC.

Making culverts great again. Efficacy of a common culvert remediation strategy across sympatric fish species

Culverts are instream structures that act as hydrological barriers to fish movement by altering water turbulence, increasing water velocities and disrupting connectivity. Hydrological barriers like culverts have led to the fragmentation and decline of freshwater fish populations worldwide. Culvert remediation strategies such as bed roughening have proved effective at increasing the likelihood of fish passage in a variety of fish species. However, little is known about whether culvert roughening is efficacious for Australian small bodied fishes and if so, whether bed roughening is comparably beneficial to all species that may utilise remediated culverts. This study assessed the effect of roughened bed substrates on the swimming performance and behaviour of four small bodied or juvenile Australian fishes (Hypseleotris compressa and Melanotaenia duboulayi, and juvenile Tandanus tandanus and Maccullochella peelii) that exist in sympatry over parts of their distribution. Results showed that bed roughening increased water turbulence and the size of low velocity regions within fluid flow and that all fish species displayed the same positive behavioural preferences for these zones. However, the effect of bed roughening on swimming endurance and traversability was found to only benefit Mel. duboulayi and Mac. peelii. Roughening decreased endurance and traversability in T. tandanus, and had no effect on performance in H. compressa. These data indicate that sympatric species may respond differently to culvert remediation actions, highlighting the need for a holistic approach to culvert remediation and a comprehensive understanding of all species’ requirements within the affected environment.

Predicting hydraulic structure-induced barotrauma in Australian fish species

When fish pass downstream through river infrastructure, such as dams and weirs, barotrauma may occur as a result of rapid decompression. In severe cases, barotrauma may lead to mortality. Different species are likely to respond differently to these decompressions. Therefore, to predict barotrauma for a specific species, surrogate species may not be a valid approach, and it may be necessary to examine each species individually. For the present study, Australian bass and carp gudgeon were exposed to a range of rapid decompressions using hyper- and hypobaric hydro-chambers and examined for injuries and mortality. Rapid decompression data from these two fish species, in addition to previously examined Murray cod and silver perch, were evaluated to determine which injuries were highly associated with and likely to predict mortality. Dose–response logistic regression models were developed for each species to predict injury and mortality over a range of rapid decompressions. These models are valuable for estimating injury and mortality rates for fish passing though river infrastructure and can be applied to specific sites where pressure profiles have been developed. Applying these models to current and future infrastructure can provide important insight into what measures or design alterations may be necessary to reduce negative effects of infrastructure on fish populations.

Deficiencies in our understanding of the hydro-ecology of several native Australian fish: a rapid evidence synthesis

Environmental flows aim to mitigate the impacts of modification of riverine flow regimes by restoring components of the natural flow regime. Explicit evidence-based cause–effect relationships between flow regimes and fish responses are required for defensible flow recommendations. However, flow recommendations are typically based on expert opinion rather than a rigorous test of the available evidence. We used rapid evidence synthesis to systematically review the literature on responses of several native Australian fish to flow-related and other important environmental variables, and tested 13 explicit hypotheses. The hypotheses were related to the condition, reproduction and survival of pygmy perches, carp gudgeons, blackfish and flat-headed gudgeons. The evidence was insufficient to reach strong conclusions for all but three of our hypotheses. Late-spring high flows are associated with increased survival of pygmy perches and carp gudgeons, and exotic fish are associated with decreased survival of these fishes. The evidence that warmer spring water temperatures enhance their reproduction was inconsistent. The dearth of evidence to support or refute most hypotheses points to substantial gaps in our understanding of hydro-ecology of these native Australian fish, highlighting the need for targeted monitoring and research to further understand key flow relationships for these fish species.

Linking the recruitment and survivorship of a freshwater stream-specialist fish species to flow metrics in Mediterranean climate temporary streams

ABSTRACTNovel modelling was utilised in the present study to reveal significant relationships between the abundance of the Australian freshwater stream-specialist fish Galaxias olidus and metrics defining flow regimes across a region dominated by temporary streams. It was revealed that increases in total abundance were linked to metrics (both 1- and 3-year periods) that indicate greater water availability and the persistence of water in pools across the year, namely the average duration of zero-flow days over the low-flow season (negatively) and total duration of bankfull flows across the year (positively). The analysis identified 3-year metrics as being more important to the abundance of 0+ fish rather than annual ones. Taken together, these findings describing the flow requirements of a stream specialist will help to guide implementation of environmental flows, but will also highlight the need for continued exploration of flow–ecology relationships.

A review of the Acanthocephala parasitising freshwater fishes in Australia.

The acanthocephalan fauna of Australian freshwater fishes was documented from field surveys, a literature survey and examination of specimens registered in Australian museums. From the 4030 fishes, representing 78 of the 354 Australian freshwater fish species (22%), examined for infection seven species of acanthocephalan were recovered. These species comprised five endemic species, three in endemic genera, two species in cosmopolitan genera, one species not fully identified and 1 putative exotic species recovered from eight species of fish. Of these Edmonsacanthus blairi from Melanotaenia splendida, was the only acanthocephalan found at a relatively high prevalence of 38·6%. These findings are indicative of a highly endemic and possibly depauperate acanthocephalan fauna. Species richness was higher in the tropical regions than the temperate regions of the country. Exotic acanthocephalan species have either not been introduced with their exotic hosts or have been unable to establish their life cycles in Australian conditions. Consequently, acanthocephalans have not yet invaded endemic Australian fish hosts.

First detection of Edwardsiella ictaluri (Proteobacteria: Enterobacteriaceae) in wild Australian catfish.

The bacterium Edwardsiella ictaluri is considered to be one of the most significant pathogens of farmed catfish in the United States of America and has also caused mortalities in farmed and wild fishes in many other parts of the world. E.ictaluri is not believed to be present in wild fish populations in Australia, although it has previously been detected in imported ornamental fishes held in quarantine facilities. In an attempt to confirm freedom from the bacterium in Australian native fishes, we undertook a risk-based survey of wild catfishes from 15 sites across northern Australia. E.ictaluri was detected by selective culturing, followed by DNA testing, in Wet Tropics tandan (Tandanus tropicanus) from the Tully River, at a prevalence of 0.40 (95% CI 0.21-0.61). The bacterium was not found in fishes sampled from any of the other 14 sites. This is the first report of E.ictaluri in wild fishes in Australia.

De novo genome assembly and annotation of Australia's largest freshwater fish, the Murray cod (Maccullochella peelii), from Illumina and Nanopore sequencing read.

One of the most iconic Australian fish is the Murray cod, Maccullochella peelii (Mitchell 1838), a freshwater species that can grow to ∼1.8 metres in length and live to age ≥48 years. The Murray cod is of a conservation concern as a result of strong population contractions, but it is also popular for recreational fishing and is of growing aquaculture interest. In this study, we report the whole genome sequence of the Murray cod to support ongoing population genetics, conservation, and management research, as well as to better understand the evolutionary ecology and history of the species. A draft Murray cod genome of 633 Mbp (N50 = 109 974bp; BUSCO and CEGMA completeness of 94.2% and 91.9%, respectively) with an estimated 148 Mbp of putative repetitive sequences was assembled from the combined sequencing data of 2 fish individuals with an identical maternal lineage; 47.2 Gb of Illumina HiSeq data and 804 Mb of Nanopore data were generated from the first individual while 23.2 Gb of Illumina MiSeq data were generated from the second individual. The inclusion of Nanopore reads for scaffolding followed by subsequent gap-closing using Illumina data led to a 29% reduction in the number of scaffolds and a 55% and 54% increase in the scaffold and contig N50, respectively. We also report the first transcriptome of Murray cod that was subsequently used to annotate the Murray cod genome, leading to the identification of 26 539 protein-coding genes. We present the whole genome of the Murray cod and anticipate this will be a catalyst for a range of genetic, genomic, and phylogenetic studies of the Murray cod and more generally other fish species of the Percichthydae family.

Genome-wide data delimits multiple climate-determined species ranges in a widespread Australian fish, the golden perch (Macquaria ambigua)

Species range limits often fluctuate in space and time in response to variation in environmental factors and to gradual niche evolution due to changes in adaptive traits. We used genome-wide data to investigate evolutionary divergence and species range limits in a generalist and highly dispersive fish species that shows an unusually wide distribution across arid and semi-arid regions of Australia. We generated ddRAD data (18,979 filtered SNPs and 1.725million bp of sequences) for samples from 27 localities spanning the native range of golden perch, Macquaria ambigua (Teleostei; Percichthyidae). Our analytical framework uses population genomics to assess connectivity and population structure using model-based and model-free approaches, phylogenetics to clarify evolutionary relationships, and a coalescent-based Bayesian species delimitation method to assess statistical support of inferred species boundaries. Addressing uncertainties regarding range limits and taxonomy is particularly relevant for this iconic Australian species because of the intensive stocking activities undertaken to support its recreational fishery and its predicted range shifts associated with ongoing climate change. Strong population genomic, phylogenetic, and coalescent species delimitation support was obtained for three separately evolving metapopulation lineages, each lineage should be considered a distinct cryptic species of golden perch. Their range limits match the climate-determined boundaries of main river basins, despite the ability of golden perch to cross drainage divides. We also identified cases suggestive of anthropogenic hybridization between lineages due to stocking of this recreationally important fish, as well as a potential hybrid zone with a temporally stable pattern of admixture. Our work informs on the consequences of aridification in the evolution of aquatic organisms, a topic poorly represented in the literature. It also shows that genome-scale data can substantially improve and rectify inferences about taxonomy, hybridization and conservation management previously proposed by detailed genetic studies.

Indirect Consequences of Recreational Fishing in Freshwater Ecosystems: An Exploration from an Australian Perspective

Recreational fishing in freshwater ecosystems is a popular pastime in Australia. Although most native fish are endemic, the fauna is depauperate compared to any landmass of similar size. With commercial fishing no longer a major industry in the country’s freshwaters, the future sustainability of these ecosystems will depend heavily on the actions of recreational fishers. However, there has been limited focus on the consequences of recreational fishing in freshwaters. There is particularly a dearth of information on the indirect consequences of fishers on the waterbodies they depend on for their sport. After outlining the respective trends in commercial and recreational fishing in Australia as a basis for placing the sport in context, the indirect impacts of fishers on water quality, movement (walking, off-road vehicles), the introduction/translocation of fauna (particularly fish), the dispersal of flora and the transmission of fish disease and pathogens are reviewed. It is concluded that with the decline of commercial fishing, the competition between commercial fin-fishing and recreational fishing is negligible, at least throughout most of the country. It is also concluded that each of the issues addressed has the potential to be detrimental to the long-term sustainability of the freshwater ecosystems that the fishers depend on for their recreation. However, information on these issues is scant. This is despite the current and predicted popularity of freshwater recreational fishing continuing to increase in Australia. Indeed, there has been insufficient quantitative assessment of the impacts to even determine what is required to ensure a comprehensive, adequate and representative protection of these freshwater ecosystems. To underpin the sustainability of inland recreational fishing in the country, it was concluded that research is required to underpin the development and implementation of appropriate policies. The alternative is that the integrity and biodiversity loss of these ecosystems will ultimately result in their collapse before the indirect consequences of recreational fishing have been directly assessed and appropriately protected. However, the lack of protection of wetlands is not restricted to Australia; there is a deficit of freshwater protected areas worldwide.

Assessing the potential for trace organic contaminants commonly found in Australian rivers to induce vitellogenin in the native rainbowfish (Melanotaenia fluviatilis) and the introduced mosquitofish (Gambusia holbrooki)

In Australia, trace organic contaminants (TrOCs) and endocrine active compounds (EACs) have been detected in rivers impacted by sewage effluent, urban stormwater, agricultural and industrial inputs. It is unclear whether these chemicals are at concentrations that can elicit endocrine disruption in Australian fish species. In this study, native rainbowfish (Melanotaenia fluviatilis) and introduced invasive (but prevalent) mosquitofish (Gambusia holbrooki) were exposed to the individual compounds atrazine, estrone, bisphenol A, propylparaben and pyrimethanil, and mixtures of compounds including hormones and personal care products, industrial compounds, and pesticides at environmentally relevant concentrations. Vitellogenin (Vtg) protein and liver Vtg mRNA induction were used to assess the estrogenic potential of these compounds. Vtg expression was significantly affected in both species exposed to estrone at concentrations that leave little margin for safety (p<0.001). Propylparaben caused a small but statistically significant 3× increase in Vtg protein levels (p=0.035) in rainbowfish but at a concentration 40× higher than that measured in the environment, therefore propylparaben poses a low risk of inducing endocrine disruption in fish. Mixtures of pesticides and a mixture of hormones, pharmaceuticals, industrial compounds and pesticides induced a small but statistically significant increase in plasma Vtg in rainbowfish, but did not affect mosquitofish Vtg protein or mRNA expression. These results suggest that estrogenic activity represents a low risk to fish in most Australian rivers monitored to-date except for some species of fish at the most polluted sites.