The multigenerational impacts of estrogenic EDCs on reproductive success and survival fitness of medaka offspring

Endocrine disrupting chemicals (EDCs) occur ubiquitously in aquatic environments, many of which can impair fish reproduction by mimicking the normal functions of hormones and potentially affect the sustainability of fish populations. Increasing evidence has also shown that many estrogenic EDCs can disturb the fish immune system. An impaired immune system could render individuals more vulnerable to pathogens, leading to increased death and reduced population size. Therefore, both immune and reproductive impairments of fish are an important consideration when assessing the risk of exogenous estrogen on fish populations. It is also essential to assess the long-term impact of exogenous estrogens on fish populations, by uncovering the persistence and reversibility of adverse biological effects on a transgenerational scale.Using the marine medaka (Oryzias melastigma) as a model organism, this study aims to provide a holistic assessment on the impacts of 17α-Ethinylestradiol (EE2), a synthetic estrogen that can be found in surface waters worldwide, on reproduction and immune function of the progeny of exposed adults. Adult medaka were exposed to a range of EE2 concentrations for different lengths of time (both short term and long term). Through monitoring fertility, fecundity, hatching success and hatching time, the reproductive success of parental exposed fish (F0 generation) was evaluated. Embryos sampled from parental EE2 exposed fish were allowed to develop continuously in EE2 or in the absence of EE2. At 7 and 14 days post hatching, a host-resistance assay to pathogenic bacteria was performed to determine the survival fitness and immune competence of the F1 larvae. Our results indicate that parental exposure of EE2 is sufficient to reduce survival fitness of progeny at an early larval stage, which occurred at concentrations lower than those required to delay hatching. The ability of developing F1 larvae to resist pathogenic bacteria was impacted by exposure to EE2 in a concentration dependent manner. To assess potential transgenerational impacts of EE2, the F1 generation was raised to adulthood, and their reproductive success was monitored, the F2 eggs were collected and raised and survival fitness and immune competence was assessed through a host-resistance assay as with the F1 generation. Our results indicate that the impact of EE2 exposure on immune function continues into the F2 generation. Subsequently, the F3 generation is being raised to adulthood, and preliminary results will be presented. These results (i) ascertain the importance of the combined observation of reproductive and immune impacts and (ii) highlight the significance of taking a multigenerational approach in understanding the impacts of exogenous estrogens on survival fitness of parents, their offspring and population sustainability.