An international collaborative research team consisting of 13 domestic research institutes such as Ryukyu University, Tohoku University, and Kyoto University and 6 research institutes from 7 overseas countries such as India and Vietnam collected medaka fish from all over the world, and the whole mitochondrial genome and nuclear gene bases. A closer look at the roots of the ricefish family from sequence analysis revealed that the origin of the ricefish was in the subcontinent of India and then spread throughout the continent of Eurasia.
According to the University of Ryukyus, the oldest divergent ricefish species found in the research of the international collaborative research team was Setonai medaka in the western garts region of western India, and all medaka fish living in Southeast Asia and East Asia were named Setonai medaka. It became clear that they had a sister relationship.
Based on fossil information, we searched for a branch between Setonai medaka and other common ancestors of medaka, and found that it was 7,400 million years ago in the late Mesozoic era when dinosaurs dominated the earth.During this period, the Indian subcontinent separated from Gondwana and moved northward in the Indian Ocean.Later, after the Indian subcontinent collided with the Eurasian continent and merged, it is believed that the ricefish family spread throughout Asia.
Ricefish belongs to the order Beloniformes, which contains halfbeaks and flying fish.Most of the fish other than medaka are saltwater fish, but it is estimated that this branch also occurred in the Indian subcontinent.The elucidation of the history of lineage evolution of medaka fish is likely to be a step toward elucidating why medaka came to live in freshwater areas in Beloniformes.
Paper information:[Biology Letters] Mesozoic origin and'out-of-India' radiation of ricefishes (Adrianichthyidae)
