Gambusia holbrooki: pest or potential bioindicator for endocrine disruption in Victorian freshwaters, Australia?

摘要

Freshwater aquatic systems are often challenged by harmful anthropogenic contaminants such as sewage effluents, agricultural pesticides, and industrial and urban run-off. Water quality monitoring is necessary to understand effects on aquatic organisms. Biological monitoring tools such as biomarkers are useful to detect effects in fish and aquatic organisms through cellular, molecular, biochemical, physiological or/and behavioural biomarkers. However, the identification of a suitable fish bioindicator is a challenge because most fish species do not have a wide distribution to enable comparisons between sites or may require a big effort to capture. Gambusia holbrooki (mosquitofish) are wide-spread around Australia and are easy to capture with dip nets. G.holbrooki responses to endocrine active compounds (EACs) have been studied in the laboratory, providing data for comparisons. In this study, the focus is on the evaluation of data gathered from the suite of biomarkers (EROD, Vitellogenin protein induction and gonopodial measurements) together with chemical analyses of the water (estrogenic and AhR activity) to understand the condition of peri-urban creeks and rivers in Victoria. The suitability of using G.holbrooki as a sentinel species for the monitoring of EACs in Australian creeks and rivers based on the biomarkers chosen for this study is also discussed. Adult male G.holbrooki were collected from February to May between 2007 to 2009 from various land use types such as urban, rural, wastewater treatment plant impacted (WWTP) and reference sites (Ref) around Victoria, using a dip net. Gonopodial indices assessed were fish body length, gonopodial length:body length ratio, R4: 6 ratio, fish body mass and absence of hooks and serrae. Vitellogenin protein induction and hepatic EROD activity were analysed in fish. Fish from a number of sites showed various effects in the gonopodial indices suggesting endocrine disruption. However, G.holbrooki are also highly plastic and adaptable to a variety of water conditions making interpretations of morphological characteristics complicated. Confounding factors such as temperature, individual site history, predator absence/presence, extreme weather conditions and other factors may have influenced fish gonopodial indices. Significant effects in vitellogenin protein and hepatic EROD activity induction were observed in fish from some of the sites. Estrogenic and AhR activity was detected at all sites including the reference sites. There was no consistent pattern observed in the water activity measurements and biomarker results. Despite the number of challenges that were encountered with the use of G.holbrooki for the biomarkers chosen for this study, results obtained were useful for G.holbrooki from the wild. Therefore it is concluded that G.holbrooki is a suitable bioindicator for estrogenic EACs for Victorian and Australian creeks and rivers. Although environmental factors may confound the results of some of the biomarkers that were chosen for this study, it should not deter the future use of G.holbrooki as a bioindicator. Instead, fish populations from affected study sites should be monitored over time with more frequent sampling to better understand natural variation. Results of this study will contribute to a long-term risk assessment study of the release and potency of estrogenic contaminants entering Victorian creeks and rivers.