Ecotoxicological effects data are lacking for hundreds of active pharmaceutical ingredients (APIs), used globally and released continually into aquatic environments following manufacture and patient use, potentially impacting wildlife, including fish, in which human drug targets are highly conserved. In the work presented in this report, a series of different transgenic (Tg) zebrafish models (embryo-larvae, 4 days post fertilisation – dpf) were applied for investigating mechanism- or MoA- directed environmental effects assessment, following exposure to selected APIs from the afore-mentioned API classes of potential concern for fish.