Oxytocin a Key Regulator of Fish's Social Behavior

Ever wondered why some species develop complex social behavior while others spend their lives alone? Well, the researchers at the McMaster University have produced an answer to this crucial evolutionary question.

According to the researchers, the hormone oxytocin that is responsible for making humans fall in love, display a similar effect on fish. Oxytocin is involved in social recognition and bonding. This hormone is a key regulator of social behavior and has evolved and endured since ancient times.

"We know how this hormone affects humans," explains Adam Reddon, lead researcher and a graduate student in the Department of Psychology, Neuroscience & Behaviour at McMaster University. "It is related to love, monogamy, even risky behaviour, but much less is known about its effects on fish."

For this study, the researchers examined the cichlid fish Neolamprologus Pulcher. Belonging to the Cichlidae family this fish is endemic to Lake Tanganyika that is found in Burundi, the Democratic Republic of the Congo, Tanzania and Zambia. This fish is rare among lake fish because it lives in permanent hierarchical social groups with a non-breeding individual that helps rear the dominant pair. The group also has helpers that look after the young and defend their territory.

These cichlids were either injected with either isotocin that is a fish version of oxytocin or a control saline solution. When these cichlids were placed in a simulated territorial competition with a single perceived rival, the researchers noticed an aggressive behavior towards large opponents, regardless of their own size in those that were treated with isotonic.

However, when placed in a larger group situation, isotocin treated fish became more submissive as they faced aggression from more dominant group members.

According to the researchers, such signals are important in this species because they pacify the dominant members of the group.

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

"We already knew that this class of neuropeptides are ancient and are found in nearly all vertebrate groups," says Sigal Balshine, a professor in the Department of Psychology, Neuroscience & Behavior. "What is especially exciting about these findings is that they bolster the idea that function of these hormones, as modulators of social behaviour, has also been conserved."

This study was published in the latest edition of the journal Animal Behaviour.