Transcriptional responses in newly-hatched Oryzias latipes associated with developmental malformations following diluted bitumen exposure

Japanese medaka (Oryzias latipes) embryos were exposed to two concentrations of the water accommodated fractions and chemically-enhanced water accommodated fractions of two types of diluted bitumen (dilbit). Chemical-dispersion did not significantly alter transcriptional responses to dilbit toxicity but may have acted through alternative mechanisms to give similar phenotypic responses, such as normal swim bladder development. This study identified novel biomarkers in fish with or without visual malformations exposed to dilbit that can be used to assess aquatic ecosystem health. Microarray analyses identified novel biomarkers and gene networks in dilbit-exposed malformed embryos that were not evident in unaffected dilbit-exposed fish or in controls. Newly-hatched medaka from both dilbit types (AWB, CLB) and treatments (WAF, CEWAF) were pooled for further transcriptomic analysis following the chronic exposure. This included Lo fish (n = 12; 4 pools of 3 fish each) that showed no visible signs of BSD (e.g., normal fish, or norm) and Hi treatment fish (n = 12) that all showed signs of BSD (i.e., malformed fish, or malf) with 40% no SB. For fish grouped for additional analyses, no malformations (i.e., normal, or norm) were reported for water control fish (normal control, or NC, n = 6 pools), and all dispersant control fish (DC, n = 3 pools) had BSD and no SB (6 to 9 pools of three fish each per treatment, Table SB1).