Episode 30: A research team developed an experiment to study emotions in a particular species of fish, the convict cichlids. The females are trained to receive two boxes in their aquarium, one with a white lid, the second with a black lid. Little by little, the fish understand that only the box with a white lid contains a reward. It is therefore opened systematically. Creating an ambivalent situation with a box with a grey lid makes it possible to measure the animal's degree of optimism based on its reactions. These small tropical fish are known to be monogamous. Therefore, a decrease in optimism is observed in the female when forced apart from its breeding male.