Five people have been arrested and four referred to prosecutors for their alleged involvement in the unauthorized cultivation of Japanese killifish genetically modified to glow in red, police said Wednesday, with the fish originating from eggs taken from a Tokyo Institute of Technology lab by a student.

The arrests are the first in Japan for an alleged violation of the Cartagena law, which came into force in 2004 to regulate the use of genetically modified living organisms, according to the Tokyo police. Dubbed "swimming jewels," Japanese killifish of different colors and shapes have become popular as aquarium fish.

The police have seized around 1,400 genetically modified Japanese killifish from related sites and confirmed that in one case, two fish had been sold for as much as 100,000 yen ($726). Although some had already been disposed of, police said there appeared to be no danger to biodiversity.

Photo taken in Tokyo on March 8, 2023, shows red-glowing Japanese killifish seized by the Tokyo Metropolitan Police Department. (Kyodo)

All nine suspects, including a 35-year-old former student at the university who was referred to prosecutors, have admitted to the charges, they said.

Among the five arrested Monday, Naoji Aoki, a 60-year-old company employee is suspected of transporting and breeding genetically modified Japanese killifish for sale between March and June 2022 without obtaining required authorization from the government.

Another suspect, Toshikazu Furukawa, 68, allegedly disposed of some of the fish in an irrigation channel in Chiba Prefecture between July and August 2022.

The police launched an investigation after receiving a tip in 2022 that genetically modified Japanese killifish had been put on sale at an exhibition in Tokyo.

The Cartagena law requires parties seeking to keep and sell modified living organisms to obtain government authorization after proving that the organisms will not negatively affect biodiversity. The law is based on the Cartagena Protocol on Biosafety to the Convention on Biological Diversity.

On Wednesday, the Ministry of Education, Culture, Sports, Science and Technology said the modified killifish were traced to eggs taken from the Tokyo Institute of Technology by a student more than 10 years ago.

The ministry said it reprimanded the university and urged it to take preventive steps in a letter, adding that it has also requested public and private universities and research entities to ensure they have implemented proper controls for modified living organisms.

Photo taken in Tokyo on March 8, 2023, shows red-glowing Japanese killifish seized by the Tokyo Metropolitan Police Department. (Kyodo)

The Tokyo Institute of Technology said in its investigative report that the former student belonged to a lab dealing with genetically modified freshwater fish between April 2009 and March 2012 and was involved in breeding and keeping the organisms.

He allegedly handed over some eggs to the mother of a fellow student at the university, which resulted in the dispersal of the genetically modified organisms.

Japanese killifish have increasingly attracted fans as they are easy to keep. They are the third most popular pets following dogs and cats, according to a 2022 survey conducted by the Japan Pet Food Association.