A species comparison of 17-α-ethynylestradiol uptake and tissue-specific distribution in six teleost fish

Differences exist among fish species in their sensitivity to endocrine disruptors such as 17-α-ethynylestradiol (EE2). We examined whether there were corresponding differences in EE2 uptake rates and short-term internal distribution patterns. Six freshwater species: Japanese ricefish (medaka, Oryzias latipes), goldfish (Carassius auratus), zebrafish (Danio rerio), fathead minnow (Pimephales promelas), Atlantic killifish (Fundulus heteroclitus) and rainbow trout (Oncorhynchus mykiss) were exposed to waterborne radiolabelled EE2 (100 ng/L) for 2-h measurements of uptake, tissue accumulation and oxygen consumption rates (MO₂). EE2 uptake rate and MO₂ were relatively consistent among species (2.5-3.0 fold variation), with the only significant differences being a lower EE2 uptake rate in medaka, and lower MO₂ in medaka, goldfish, and zebrafish relative to the other species. EE2 accumulation, however, exhibited two distinct patterns, suggesting differences in metabolic processing. In killifish and medaka, the highest accumulation (~ 50%) occurred in the liver and gallbladder, whereas in minnow, goldfish, zebrafish and trout, > 50% accumulated in the carcass. No significant sex differences were found in killifish or minnow, apart from lower gill tissue EE2 accumulation in minnow females. This study demonstrated that metabolic processing of EE2 may be species-specific and tissue specific EE2 distribution profiles vary. These could be indicative of differences in overall EE2 sensitivity among species.