Dominant males in Indonesian fish species can turn black when agitated. The ricefish, Oryzias celebensis, wants to assert its dominance with this move, he wrote Live Science.
The researchers created three tanks to test the conditions in which males remained dark. There were two tanks covered in algae – one with two males and one female and one with three males. The third had no algae, only two males and one female.
The fish in the algae tank constantly attacked each other, but not the other, suggesting that the animals may need some sort of cover to feel safe when attacked. Experts also noted that the fish that left a black mark attacked everyone, while only the male that did not turn black attacked his companions without a mark and the females.
This is not the first species of fish in which a similar phenomenon was observed during the interaction of cells containing pigment granules with neurotransmitters.
For example, in rainbow guppies, the eyes of the dominant fish turn black when it prepares to attack its rival. Robert HeathcoteAccording to a biologist from the University of Oxford, however, in many cases it is the change in color that indicates dependence: the appearance of black bands in the marbled chick is more indicative of victims.