Fish eye guppies blacken with anger
Biologists have found that the color of the irises of the eyes of popular aquarium fishes guppy (Poecilia reticulata) can vary from silver to black depending on mood. Scientists believe that this allows the animal to transmit a signal of threat in that case, if they are aggressive. The paper was published in the journal Current Biology.
Freshwater guppies in the natural environment they live in South America and on some nearby Islands. They are at the bottom of the food pyramid, they are hunted by many predators, and between fish often fight for resources. In previous studies it was shown that fish with dark eyes behave more aggressively and dominate. However, it remained unclear whether they deliberately change the color.
“To investigate experimentally the colors of the eyes of animals can be very difficult, so we have produced a realistic-looking robolab with eyes of different colors in order to study the reactions of these fish,” explains lead author Robert Heathcote from Exeter University in the UK. It turned out that a large rabaraba with black eyes frightened guppies from food. At the same time, rabaraba with black eyes, but smaller than the real size of guppies were attacked themselves.
The authors believe that this is because black eyes — a signal of “fair” aggression. In this case, the animal indicates not only that they are ready to engage in confrontation with other individuals, but about owning something valuable. That is why the group attacked a small rabaraba — they had little doubt in his victory and wanted what she was hiding. In nature, guppies do not show black eyes large of individuals, but only those over which it can dominate.