Fish separated from their mate pine for each other and become pessimistic, scientists have found for the first time, challenging the belief that sexual emotional attachment is unique to humans.
Researchers at the University of Burgundy in France allowed 33 convict cichlids to spend two days choosing a mate, then monitored their behaviour for three weeks when they were paired with a fish that they had not picked.
The experiments showed that when females were kept away from their preferred mate they spawned later, spent less time looking after their eggs and had fewer fry.
In a second test, the fish were taught to open a black box containing food, and leave a white box which was empty.
But when presented with an ambiguous grey box, the fish that had been separated from their partner took nearly twice as long to look in the box, proving that they were feeling more pessimistic about life, the scientists said.
“There is increasing evidence that non-human animals experience similar emotions to humans,” wrote lead author Dr Chloé Laubu in the journal Royal Proceedings of the Royal Society B.
“Our results suggest that the relationship between affective state and pair-bonding has evolved not only in humans but also in at least one other monogamous species, the convict cichlid.”
The convict cichlid Amatitlania siquia, which is native to Central America, was chosen because it is a monogamous fish which forms long-lasting pairs with strong cooperation between parents for parental care.
Males grow to be around 6.5 inches (17 cm) long and females closer to 4.5 inches (11 cm) long.
Young usually take around six months to mature, during which time both mother and father carry out several parenting tasks including driving away intruders and fanning eggs to give them more oxygen.
Once hatched the parents allow their offspring to feed at night then retrieve their young just before dark, sucking up three or four at a time and delivering them back into the nest.