The present invention relates to a transgenic fish having at least one genomically integrated expression cassette containing a 5′-regulatory nucleotide sequence responsive to hormones, particularly estrogenic hormones, connected in a functional manner upstream of a nucleotide sequence encoding a reporter protein. The present invention further relates to methods of using the transgenic fish for various purposes, including, for example: (1) identifying estrogenic endocrine disruptors; (2) monitoring estrogen-like activity of test samples; (3) identifying anti-estrogenic endocrine disruptors; and (4) investigating the effects of endocrine disruptors on liver regeneration. Expression cassettes, host cells, and transgenic cells of aquatic animals are also disclosed.