The effects of Endocrine Disrupting Chemicals (EDCs) on the native Australian fish Murray River rainbow fish (Melanotaenia fluviatilis)
Creators: name: Pereira Miranda, Ana Filipa
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 310909
subject: Animal physiology - cell
classificationCode: 310914
subject: Vertebrate biology
classificationCode: 410402
subject: Environmental assessment and monitoring

description: Chemicals that have the ability to interfere with the endocrine system of organisms are termed endocrine disrupting chemicals (EDCs). The endocrine system requires a fine and orchestrated control of hormones to further control vital processes such as metabolism, growth or reproduction. This research evaluated the effects of several endocrine disrupting chemicals in the aquatic environment, such as 17α trenbolone, atrazine, propylparaben, pyrimethanil, estrone and 17α estradiol on the reproductive health of the native Australian fish Murray River rainbowfish (Melanotaenia fluviatilis); in response to the severe lack of research on native species. Diverse mixtures of endocrine disruptors were also assessed in order to attain a more realistic case scenario. In breeding groups of fish exposed to 4, 40 and 400 ng/L of the feedlot contaminant 17α trenbolone for 10 and 21 days, vitellogenin concentrations were significantly reduced at 40 ng/L at day 10; and 400 ng/L at the end of the exposure (21 days), highlighting the non-dose response effects of 17α trenbolone. Fecundity was significantly reduced and after 17 days of exposure eye and spinal deformations occurred on and were observed from day 2 after hatching in about 20% of larvae. By the end of the exposure period, gonads of female fish exposed to 400 ng/L of 17α trenbolone showed an increased number of atretic follicles when compared to the control. A further exposure of both male and female M. fluviatilis to 40 and 400 ng/L of 17α trenbolone for 14 days showed a significant decrease in plasma vitellogenin in females. In another experiment, vitellogenin mRNA was induced with exposure to 40 ng/L in male fish and the expression of brain aromatase (cyp19a1b) was significantly induced at both 40 and 400 ng/L of 17α trenbolone. In females, at 40 ng/L a decrease in brain aromatase expression cyp19a1b was observed. In the ovary, the expression of the ovarian aromatase (cyp19a1a) was significantly downregulated at both 40 and 400 ng/L of 17α trenbolone. The exposure of M. fluviatilis eggs to different concentrations of 17α trenbolone (until hatching) resulted in several abnormalities in hatched larvae though there was no dose-response in the percentage of abnormalities observed. Undeveloped eyes, as well as spinal deformations, were observed at exposure concentrations of 31.2, 125 and 500 ng/L. The results indicate that 17α trenbolone may have effects beyond its androgenic action and act also as a genotoxic compound at concentrations commonly found in effluents from feedlots. The effects of 17α trenbolone on both egg and larvae can additionally impair population fitness at relatively low concentrations. When the androgenic chemical 17α trenbolone was mixed with an estrogen, 17β estradiol, for 7 days it was demonstrated that 17α trenbolone was unable to activate the estrogen receptors. When circulatory levels of vitellogenin were investigated, it was clear that 500 ng/L of 17α trenbolone was partially able to counteract the effects of 50 ng/L of the estrogen 17β estradiol at measured protein levels although no interaction was observed at the molecular level. When exposed to atrazine, the gonadal development and maturation of rainbowfish were disrupted. Since these effects are also under hormonal control it is possible that pathways other than the estrogen receptor binding are also susceptible to disruption. This was clear of at ecologically relevant concentrations atrazine exposure with effects on gonadal maturation in females, and a significant increase of spermatogonia in the male gonads of fish exposed to 13 and 130 µg/L of atrazine for 14 days; whereas there were no effects on vitellogenin levels. Similarly, when fish were exposed to mixtures of chemicals, in 21-day exposures, a multiparameter approach was essential to understand the effects of chemical mixtures on the fish, with alterations in gonads and liver being observed in fish exposed to pyrimethanil and mixtures of chemicals while vitellogenin levels remained unaltered. Only estrone and EE2 induced increased levels of vitellogenin in the plasma of M. fluviatilis while deleterious effects on the gonads were evident from tissue histopathology in exposures to pyrimethanil and atrazine. This is conclusive evidence that these chemicals have the ability to disrupt other pathways not simply the classically “expected” binding to an estrogen receptor Further evidence that some chemicals are able to disrupt multiple pathways was also demonstrated after exposure of M. fluviatilis to 0.01-10 mg/L of perfluorooctanoic acid (PFOA). Although PFOA was slightly estrogenic leading to the induction of circulatory levels of vitellogenin in male fish after 14 days of exposure, this chemical was also able to interfere with the thyroid pathway and lead to changes in antioxidant processes. This study highlights that investigations into possible effects of EDCs on physiological targets other than reproduction in fish are essential. There are even fewer studies of their effects on other aquatic species. To date, in research even on teleosts, there is still some uncertainty as to the structure and function of some of the naturally occurring hormones and the endocrine glands themselves, making the assessment of the impact of EDCs, in aquatic ecosystems, even more difficult.