Female cichlids, a small fish from South America, become pessimistic when they can’t be with their first-choice mate

We are not the only species whose mood sinks when a romance goes awry. Fish, it emerges, also pine for lost sweethearts.

Female cichlids, a small fish from South America, become pessimistic when they are not allowed to be with their first-choice mate and must instead endure a kind of forced marriage to a lesser male, research has shown.

The study is thought to be the first to show that the outlook of a fish can depend on their sexual partner.

Centuries of poetry will attest to how star-crossed humans suffer when denied their true love. Proving a similar effect in the animal kingdom required a clever experiment, capable of divining a fish’s state of mind.

Judging which male a female cichlid preferred was straightforward.