The bluegill bream given to Japan's emperor in a US visit are threatening the country's native fish species, it has been revealed.
Emperor Akihito has admitted that he is "deeply troubled" that the fish had escaped Japanese research centers, where the emperor had hoped they could be bred for food.
The emperor brought the notoriously aggressive fish back to Japan as a gift in the 1960s.
"In those days, we had high expectations of raising them for food, and I'm deeply troubled by how it turned out," he told journalists at a Speech in Otsu, Japan on Sunday.
Supplies of local delicacies in Japan's Lake Biwa, such as the crucian carp, have suffered following the fish invasion, local fisheries official Koichi Fujiwara told the International Herald Tribune.
The aggressive Bluegill bream are distinguished by their blue or black "ear" markings, with males reportedly changing their color to imitate females in mating season to prevent attack from other males' guarding nests.
The disguised fish then sneakily spawn with the nests' eggs.
