Researchers in France have found a small tropical fish that has a big heart that suffers when separated from its lover.

Meet the tiny Central American convict cichlid known to be a loyal and monogamous partner. Experts believe that these fishes have developed being very loyal to their partners as a way to better protect their young, who are extremely vulnerable to predators.

Scientists observed that when paired with a male cichlid they do not prefer, female cichlids often exhibit “pessimistic” behavior.

The convict cichlid is known as a loyal lover (AFP/Sam Yeh)

In an experiment to measure the fish’s mental response to separation, researchers from the University of Burgundy in Dijon trained the female cichlids to use their mouths to open two small boxes placed on either side of their tanks.

The boxed were labeled the ‘positive’ and the ‘negative’ boxes, which had either black or white lids to help the fish distinguish them from each other. The ‘positive’ box had fish food inside, while the ‘negative’ box was empty.

Then, a grey ‘ambiguous’ box was placed in the center of the tank to take a look at how the female cichlids would react.

To effectively measure each fish’s mental response to separation, researchers from the University of Burgundy in Dijon trained females to use their mouths to open two small boxes, placed either side of their tanks. (AFP File Photo)

The scientists reasoned that the fishes who had an optimistic outlook would have opened the grey lid in the hope of having a treat, but pessimistic ones might have hesitated or left the box alone.

The study published in the journal Proceedings of Royal Society B, shows that the female cichlids spend more time trying to lift off the grey lids when their “favored males” were with them.

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