Cloned Fish Raised Together Develop Distinct Personalities As They Grow Up

Schooling fish move together with such precision that it looks like instinct. A new study on clonal mollies is testing that assumption. The fish start out as individuals, and it takes a month for them to become a coordinated shoal.

But here is the surprise: groups of genetically identical clones begin to behave differently after a few weeks.

What the Study Found

Clonal mollies are clones, meaning every fish in a group shares the exact same genes. Researchers expected that would mean uniform behavior. Instead, they found distinct patterns emerging over time.

During their first days of life, the fish still show individual habits. Around one month of age, the fish begin to form cohesive shoals. That is when the coordinated movements typical of the group appear. What the researchers noticed was not just a delay. Several shoals of genetically identical clones began to behave differently after a few weeks. The way they moved, the way they responded to threats, the way they gathered and split apart — all of it diverged.

Why It Matters

The study suggests that schooling is not entirely hardwired. It raises questions about how animals develop social behavior, and whether genetics alone determines how a group acts.

What We Know So Far

• Schooling behavior emerges gradually, not instantly
• Clonal mollies show individual habits in their first days
• Cohesive shoals form around one month of age
• Genetically identical groups diverge in behavior after a few weeks
• The study suggests schooling may not be purely instinctual

The Bigger Picture

The study is a reminder that even the most coordinated natural systems can hide unexpected complexity beneath the surface. A school of fish may look like one organism, but it is made up of individuals. The study raises more questions than it answers. How much of schooling is learned? How much is inherited? What triggers the shift from individual to group behavior?

For now, the takeaway is simple: even identical clones can grow up to be very different. The study shows that schooling is not simply instinct. It is a process that develops over time.

Source material: “Groups of genetically identical fish follow different behavioral paths as they mature,” Phys.org.

behavioral biology · clones · genetics · instinct vs learning · schooling fish