Carotenoids in Youkihi-medaka, a mutant of Minami-medaka (Oryzias latipes)

The aquarium fish Youkihi-medaka is a mutant of Minami-medaka (Oryzias latipes) characterized by its scarlet body color. Comparative analysis between Youkihi-medaka and Hi-medaka was performed on the following: scale chromatophores, quantifying carotenoids within the body, and changes to the body color due to feed containing carotenoids. Chromatophores in the scales of both Youkihi-medaka and Hi-medaka were primarily yellow, and none was black. However, pigment granules within the yellow chromatophores of Youkihi-medaka appear reddish orange in contrast to the pale yellow of Hi-medaka. Analysis by HPLC revealed that the quantities of the carotenoids, astaxanthin, zeaxanthin, and lutein were found to be higher in Youkihi-medaka than in Hi-medaka. Astaxanthin, in particular, exhibited a concentration 10 times greater in Youkihi-medaka than in Hi-medaka. When astaxanthin was added to the feed, the hue value of the dorsum of the head in both Youkihi-medaka and Hi-medaka decreased significantly. These results show that the scarlet body color of Youkihi-medaka is related to abundant carotenoids and that the redness is further intensified by the intake of carotenoids.