usually, Poecilia reticulata's eyes are beautiful silver (iris part), but sometimes their eyes suddenly turn black.

(photo source: EDGAR SU /REUTERS)

it is said that the color of the eyes changes so rapidly that the fish's eyes may suddenly change color in the blink of an eye. The exact mechanism behind this eye discoloration is unclear, and perhaps peacock fish control the size of pigment cells through nerves.

in the past, scientists have observed that blackened eyes seem to be a sign of "anger" in peacock fish-individuals with blackened eyes are always more aggressive. A recent study validates this.

what kind of message does the blackening of the eyes convey between these little fish? In order to verify this, the researchers specially made a robotic fake fish that can adjust the color and size of the eyes (their original idea was to directly make a "cosmetic contact lenses" for live fish, but the plan ended in failure. ).

(it's still too difficult to stick contact lenses. Photo Source: Robert Heathcote)

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Experimental results show that blackening does deter other fish, but there is a price to pay if you use it rashly. When the experimental robot fish is larger than other fish, blackening eyes can reduce the situation in which other fish compete for food from it. But if the black-eyed fish has a smaller head than the fish around them and seems ineffective, then other fish will come forward more often and try to rob it of its food. Blackened eyes may be more like a "fight if you can" challenge than "angry".

this is a cold knowledge I read recently. unfortunately, the original paper does not provide a video of the discoloration process of peacock fish eyes, and I would like to see how fast it is.

confirm that it is a fish that wants to fight.

original study: https://www.cell.com/current-biology/fulltext/S0960-9822(18)30550-5

related report: https://www.theatlantic.com/science/archive/2018/06/guppy-eyes-they-feel-the-anger-between-you-and-i/561899/