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Previous studies exposing fish to xenoestrogens have demonstrated vitellogenin (VTG) induction, delayed gametogenesis, altered sex distribution, and decreased reproductive performance, with a majority of those studies focusing on exposure to single chemicals. The objective of this study was to determine the effects of binary mixtures of a weak estrogen receptor agonist, nonylphenol (NP) and a potent estrogen receptor agonist, 17α-ethinylestradiol (EE) on sex distribution, gametogenesis, VTG induction, heat shock protein 70 (HSP70) expression and reproductive capacity in zebrafish (Danio rerio). Fish were exposed from 2 to 60 days post-hatch (dph) to nominal concentrations of 10 or 100 µg/l NP (NP10 or NP100, respectively), 1 or 10 ng/l EE (EE1 or EE10, respectively), 1 ng/l EE + 10 or 100 µg/l NP (EE1+NP10 or EE1+NP100, respectively), 10 ng/l EE + 10 or 100 µg/l NP (EE10+NP10 or EE10+NP100, respectively) or solvent control (0.01% acetone v/v) in a static-renewal system with replacement every 48h. At 60 dph, fish from each treatment were euthanized for histological examination of gonads, and whole body VTG and HSP70 levels. Remaining fish were reared in clean water until adulthood (240 dph) for breeding studies. In all EE10 exposure groups (EE10, EE10+NP10 and EE10+NP100), increasing NP concentration acted less than additively to the action of EE in terms of VTG induction at 60 dph. Similarly, a less than additivity of effect was observed with egg production, where EE1+NP100 exposure resulted in significantly more eggs produced per breeding trial than EE1 alone. Histological staging of oogenesis revealed suppressed gametogenesis in females at 60 dph. There were no differences among treatment groups in whole body HSP70 expression in 60 dph fish or in gonadal HSP70 expression in adult fish. Although there was no statistical evidence of non-additivity, breeding trials in adults revealed significant reductions in egg viability, egg hatchability and/or F1 swim-up success, suggesting that developmental exposures to xenoestrogens may cause irreversible effects on egg quality and progeny even after depuration. In conclusion, these results suggest that environmentally relevant mixtures of NP and EE can produce additive or non-additive effects depending on the particular response being determined and the respective exposure concentrations of each chemical. Thus, it is recommended that caution be exercised in ecological risk assessments when assuming additivity in piscine responses to xenoestrogen mixtures.

Previous studies exposing fish to xenoestrogens have demonstrated vitellogenin (VTG) induction, delayed gametogenesis, altered sex distribution, and decreased reproductive performance, with a majority of those studies focusing on exposure to single chemicals. The objective of this study was to determine the effects of binary mixtures of a weak estrogen receptor agonist, nonylphenol (NP) and a potent estrogen receptor agonist, 17α-ethinylestradiol (EE) on sex distribution, gametogenesis, VTG induction, heat shock protein 70 (HSP70) expression and reproductive capacity in zebrafish (Danio rerio). Fish were exposed from 2 to 60 days post-hatch (dph) to nominal concentrations of 10 or 100 µg/l NP (NP10 or NP100, respectively), 1 or 10 ng/l EE (EE1 or EE10, respectively), 1 ng/l EE + 10 or 100 µg/l NP (EE1+NP10 or EE1+NP100, respectively), 10 ng/l EE + 10 or 100 µg/l NP (EE10+NP10 or EE10+NP100, respectively) or solvent control (0.01% acetone v/v) in a static-renewal system with replacement every 48h. At 60 dph, fish from each treatment were euthanized for histological examination of gonads, and whole body VTG and HSP70 levels. Remaining fish were reared in clean water until adulthood (240 dph) for breeding studies. In all EE10 exposure groups (EE10, EE10+NP10 and EE10+NP100), increasing NP concentration acted less than additively to the action of EE in terms of VTG induction at 60 dph. Similarly, a less than additivity of effect was observed with egg production, where EE1+NP100 exposure resulted in significantly more eggs produced per breeding trial than EE1 alone. Histological staging of oogenesis revealed suppressed gametogenesis in females at 60 dph. There were no differences among treatment groups in whole body HSP70 expression in 60 dph fish or in gonadal HSP70 expression in adult fish. Although there was no statistical evidence of non-additivity, breeding trials in adults revealed significant reductions in egg viability, egg hatchability and/or F1 swim-up success, suggesting that developmental exposures to xenoestrogens may cause irreversible effects on egg quality and progeny even after depuration. In conclusion, these results suggest that environmentally relevant mixtures of NP and EE can produce additive or non-additive effects depending on the particular response being determined and the respective exposure concentrations of each chemical. Thus, it is recommended that caution be exercised in ecological risk assessments when assuming additivity in piscine responses to xenoestrogen mixtures.

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The specificity of a medaka vitellogenin (Vtg) enzyme-linked immunosorbent assay (ELISA) kit was tested on adult hybrid tilapia to determine if vitellogenin could be successfully measured in tilapia using this method. Adult hybrid (Orechromis niloticus x Oreochromis mossambicus x Oreochromis aureus) tilapia were injected with 17â-estradiol (E2) at 5 ìg/g body weight (b.w.) in two separate experiments and exposed to 2.5 ìg/g b.w. E2 through aquaria water in a third experiment. All fish were exposed to solvent controls (50/50 PBS/ethanol, or 59/41 PBS/ ethanol) proportional to the volume of estradiol solvent used. Experiment 1 was terminated due to a decrease in fish health and unexpected mortalities. Experiment 2 was continued though there was again a decrease in fish health and mortalities before experiment was completed. According to one-way ANOVA, Experiment 2 treatment groups were significantly different (P<0.05); however, Tukey's pairwise comparisons showed no differences between treatment groups. Experiment 3 results showed statistical differences between some treatment groups (P<0.001). However, maximum vitellogenin levels reached 1250 ng/mL Vtg, which were much lower than induced vitellogenin levels from literature (0.002 mg/mL to 6 mg/mL). Typical induction trends should be as follows: male control<female control< induced male<induced female; however, these trends were not observed in this study. For these reasons, the medaka vitellogenin ELISA kit was determined not specific to tilapia vitellogenin. This research was performed due to the fact that tilapia are farmed worldwide, and to increase research with these fish, in order to better understand their response to xenobiotic chemicals, easier methods are desired for measuring their vitellogenin. Vitellogenin induction from exposure to the chemotherapeutics: oxytetracycline, Romet-30®, and copper sulfate was evaluate using Japanese medaka (Oryzias latipes). Medaka were exposed to E2 (0.0552 ìg/L) in aquaria water as a positive control. Medaka were fed oxytetracycline medicated feed at 0.0174 g, 0.0348 g, and 0.087 g, and Romet-30® medicated feed at 0.0261 g, 0.0522 g, and 0.1305 g daily for 11 days and 5 days as recommended. Medaka were exposed to copper sulfate at 1.85 mg/L for one hour (for 1 day, 7 consecutive days, and every three to five days for a total of 7 doses). Vitellogenin levels were measured using a sandwich ELISA. As expected, Vtg levels were induced from exposure to E2 (P<0.01); however, exposure to the chemotherapeutic compounds did not induce elevated Vtg levels. Alternately, copper sulfate exposure for one hour for 1 day did show a significant decrease in vitellogenin (P<0.01). Biological variation accounted for large portions of the variation within treatment groups in medaka vitellogenin in fish exposed to chemotherapeutics (as high as 41.01%). From this research we suggest that these chemicals do not have estrogenic properties capable of inducing vitellogenin in medaka. / Master of Science