Under Cartagena Protocol domestic law, genetically modifi ed (GM) fi sh have not yet received permission to be imported
or sold in Japan. However, it is anticipated that ornamental, fl uorescent GM fi sh will be imported and sold prior to any
offi cial process for evaluating their eff ects on biological diversity as GM organisms (GMO). Therefore, we have devised a
method for detecting GM fi sh that utilizes PCR for the detection of replication origins of plasmids that generally exist as
transgenes integrated in the GMOs’ chromosomes. Using red fl uorescent zebrafi sh (rfZF), sold in Japan, and rpsL GM ZF
established by us, we demonstrated the feasibility of this method for detecting GMO. Next, we examined the biological
characteristics of the GM rfZF. They were able to cross with non-GM ZF; the red fl uorescence was inherited by their progeny
according to expected outcomes, based on Mendelian genetics. Examination of the low temperature tolerance of rfZF and
non-GM fi sh indicated that the lethal, minimum temperature was the same for both fi sh (5°C). These fi ndings suggest that
the transgene of the rfZF could spread among wild-type ZF, and that these ZF could overwinter in the southernmost part of
Japan. We conclude that a continuous monitoring is required