Clownfish make solid dads and, much like the protagonist in “Finding Nemo”, will go to great lengths to protect their offspring, according to a new study. The findings, published in Hormones and Behavior, describe how male clownfish take the lead in nurturing their offspring, and suggest that the hormone isotocin, the fish version of the “love hormone” oxytocin, likely plays a role in turning clownfish brains toward fatherhood.
“Before this study we knew that clownfish fathers did most of the caring for the eggs—like Nemo’s dad!” coauthor Justin Rhodes, a neuroscientist at the University of Illinois, told Fatherly. “But we didn’t know which chemical changes needed to take place in the brain to promote the high levels of parenting behavior.”
While most male fish abandon their young (if they don’t straight-up eat them) anemone-based species like clownfish are primarily nurtured by their fathers. Male clownfish nip at their eggs to remove debris and fan the water above their nests to circulate oxygen-rich water. One recent study reported that male clownfish adopt abandoned nests—fanning and nipping eggs that aren’t even their own.
Researchers have long suspected that isotocin plays a role in this surprising paternal behavior. To test that hypothesis, Rhodes and his team injected eight male clownfish with a drug that blocks isotocin, and injected another eight fish with a simple saline solution. While the latter eight fish continued fathering as before, the isotocin-deprived fish stopped taking care of their young. “When you block isotocin or oxytocin from interacting with its receptors, levels of mothering and social bonding go down,” Rhodes says.
The results suggest that isotocin may be part of a biological system that spurs male clownfish to take on paternal responsibilities. Whether there’s a similar pathway behind human fathering, however, remains subject to debate. Prior studies have described a parenting brain network in humans that features a generous amount of oxytocin, but such findings are preliminary.
“One could conduct a similar study in humans…to see if fathering levels go down and up like they did in the clownfish,” Rhodes says. “Our results likely will translate to other vertebrates including humans.”