One species of medaka fish (also known as rice fish) is small in size and white in color and is found in southwest Sulawesi in Indonesia. They have a high level of sexual dimorphism, meaning that males are very different from females. The research team found that males exhibit distinctive black markings on their fins and flanks, and the brightness of these markings can change within seconds.
To further investigate the cause of the color change, the scientists conducted three experiments. The first was set up in an algae-covered aquarium with one female and two males. The second had only three males, and the third had two males and one female, but no vegetation.
It appeared that the males attacked each other equally regardless of whether females were present in the tanks. In a transparent aquarium without algae, neither attacks nor color changes were observed.
The number of attacks of males with black markings was higher than that of either unmarked males or females. This suggests that males with black markings are more aggressive than their uncolored counterparts.
