Japanese rice fish or medaka Oryzias species (Actinopterygii: Beloniformes: Adrianichthyidae), probably originating from breed-improved aquarium individuals, collected from a paddy field in Ehime prefecture, Japan

Abstract

Fish individuals with a small body showing various coloration such as yellow or orange, white or cream, and bluish, were observed in a paddy field in Matsuyama-shi, Ehime prefecture, Shikoku district, Japan in July, 2023. Ten of them were collected and were regarded, based on their morphology, as breed-improved aquarium individuals of the Japanese rice fish or the medaka Oryzias species (Actinopterygii; Beloniformes; Adrianichthyidae). The medaka fish of the present case were thought to have been abandoned by breeders or related person(s). Abandonment of breed-improved medaka fish might lead to genetic contamination as alien species to individuals native to that area.