Fish Form of 'Love Drug' Guides Social Decisions

Oxytocin is a hormone believed to boost social bonding, cooperation, love, monogamy and even risky behavior in humans. A new study found that a form of the so-called "love drug" helps fish navigate social situations, suggesting the hormone has had an enduring behavioral role in vertebrates.

"We already knew that this class of neuropeptides are ancient and are found in nearly all vertebrate groups," researcher Sigal Balshine of McMaster University in Canada said in a statement. But the new findings, published this month in the journal Animal Behaviour, suggest the hormones' function also has been conserved, Balshine explained.

The researchers examined the cichlid fish Neolamprologus pulcher, of Lake Tanganyika in Africa, which form permanent hierarchies made up of a dominant breeding pair and several helpers that look after the young and guard their territory.

In the study, the cichlids were injected with isotocin (the fish form of oxytocin) or a control saline solution. When pit against a rival in a fight over territory, the fish pumped full of isotocin were more aggressive towards large opponents, regardless of their own size. And when put in a large social situation, the isotocin-treated fish became more submissive to aggressive dominant fish, the study found. Placating the higher-ranking members of the group helps keep the fish societies cohesive, the researchers said.

"The hormone increases responsiveness to social information and may act as an important social glue," Adam Reddon, another McMaster researcher, said in a statement. "It ensures the fish handle conflict well and remain a cohesive group because they will have shorter, less costly fights."

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