PROBLEM TO BE SOLVED: To provide genetically modified killifish reacting to a very low concentration of estrogen, a method for creating killifish that forms thrombus using the killifish, killifish that forms thrombus created by the method, and a method for testing a substance having an estrogen-like effect using the above killifish.
SOLUTION: The killifish is (1) genetically modified killifish into which a polynucleotide having a specific base sequence derived from killifish is transduced. The method is (2) a method for creating killifish that forms thrombus comprises making genetically modified killifish (1) grow in the presence of estrogen. The killifish forming thrombus is killifish which is created according to method (2) and forms thrombus. The testing method is (4) a method comprising the steps of making genetically modified killifish (1) grow in test water, and observing if thrombus is formed in the killifish or not in a method for testing a substance having of estrogen-life effect.