The gut microbiome influences the development of social skills later in life, a recent study in fish has found. Fish that have delayed microbiome development show distinct differences in their brain structure and behavior compared to those with appropriately timed development.

Researchers studied zebrafish, which are naturally social, to see how the microbiome affected the animals' behavior. Using a special type of zebrafish that lacked a microbiome, they inoculated one group of fish with bacteria immediately after birth to promote microbiome development. They delayed the inoculation of another group of fish by one week.

They found that the fish that had delayed microbiome development exhibited more neural circuits in their brains and fewer microglia – a type of immune cell that “prunes” the brain and is necessary for normal development. These fish were also less social than the fish that had appropriately timed microbiome development.

This study suggests that the microbiome influences the social behavior of zebrafish by reducing microglial pruning. Although the study was conducted using fish, other research suggests that these findings could translate to mammals, including humans. Learn more about the role of the gut microbiome in this episode featuring Dr. Eran Elinav.

• Read study abstract.