Young guppies need social interaction as their brains develop. But does watching other fish on a screen count?
Researchers in Stockholm raised young guppies for 20 days under three conditions – live companions, fish on a screen, or near-isolation – then measured their brains. The screen group’s result was not what researchers expected.
A model for brain growth
That question drew a research group at the Department of Zoology at Stockholm University. Olivia Carmstedt, who led the project for her master’s thesis, wanted a setup where a young animal’s whole social world could be controlled.
Their subject was the guppy, a small freshwater fish common in home aquariums. Guppies make good models because they show strong brain plasticity.
“Fish are excellent models for studying brain plasticity because their brains continue to develop throughout life,” said Niclas Kolm, a professor in the department and the study’s senior author.
The human side is harder to study. Large studies tracking thousands of children link heavier screen use to delays in language and problem-solving. But a study like that can only flag a pattern, never prove the cause.
________________________________________________________________________
Three guppy childhoods
Over 20 days, young guppies grew up in one of three settings. One group lived beside a tank of live fish they could see and react to. Another watched a video of fish on a screen, and the last had almost no company at all.
The key comparison sat with the middle group. Video gave those fish the same sights – the look and movement of other guppies – but none of the back-and-forth of a real encounter.
Everything else stayed identical across the tanks. Same food, same water, same light. The only thing that changed was the kind of company each fish kept.
Guppy brain development
When the team measured the brains afterward, the gap was plain. Fish raised next to live company grew brains almost 6% larger than those that had only watched a screen.
The live-fish group also grew relatively larger olfactory bulbs – a brain region that helps process smell and social signals in fish. It enlarged only when the company was real.
Strangest of all was the screen group’s result. Their brains did not land halfway between the live-companion and isolated fish. They looked far more like the brains raised in near-isolation.
The value of interaction
Earlier research had already tied a guppy’s social world to its behavior and cognition – one study raised fish in groups of different sizes.
What this work added was a clean split between merely seeing other fish and interacting with them.
A screen offered all the visual information but never reacted. Real fish do: they turn toward you, dart off, double back. That give-and-take seems to be what a growing brain craves.
“The interaction itself, the fact that another individual responds to you in real time, appears to be important for normal brain development,” said Carmstedt.
Watching alone did not carry the same weight.
One test, no difference
Bigger brains did not mean better scores everywhere. After the 20 days, the fish took an object permanence test. That means tracking a target that briefly slips out of sight – the same skill that helps a baby understand a hidden toy still exists.
Every group did about the same. Screen-raised, isolated, live-company – all three tracked the vanishing object equally well, whatever their brain size.
That split hints that social experience shapes some parts of brain development more than others. Why the larger brain and bigger olfactory bulbs made no difference here is still an open question.
Lessons beyond the tank
None of this proves a tablet harms a human child. People are not guppies, and a cartoon is nothing like a live playmate. Even so, the finding lands squarely in the debate over screen time and the developing brain.
What the fish hint at is a difference in kind, not just amount. A video call with a grandparent, where each person reacts to the other, may give a young brain something passive watching cannot.
The notion that early experience changes specific brain regions is not new.
In other animals, what a young brain takes in can physically enlarge the areas handling those signals, as one review of smell development in mice describes.
Open questions remain
Before this work, the human numbers could only show that screens and brain differences travel together. The fish experiment offers what those studies could not: live interaction, not just the sight of others, supports normal guppy brain development.
That opens clear next steps. Scientists can now ask which parts of live interaction count most, how long the effect holds, and whether the same pattern appears in animals closer to us.
For now the lesson is narrow but firm. In a young guppy, a screen full of fish was no substitute for a single live companion that swam back. Whether the same holds for a toddler and a tablet is the next thing worth testing.
The study is published in the journal Biology Letters.
NOTE – This article was originally published in Earth and can be viewed here
