The environment that young zebrafish experience influences both the shape and electrical activity of eye neurons, which in turn influences their subsequent behavior.
Neuroscientists at King’s College London studied five-day-old fish to investigate whether the visual features of the environment in which they grew up influenced the development of eye cells. The study, published in Neuron, found that fish that grew up surrounded by horizontal stripes developed neurons with different shapes and responses compared to fish that grew up surrounded by vertical stripes.
Using a virtual reality behavioral test developed in collaboration with the University of Konstanz, the researchers showed that structural and functional differences in neurons influence fish behavior. Zebrafish have an innate preference to swim toward stripes that are parallel to their body orientation. The study used virtual reality to test the strength of this preference and found that this instinct was significantly reduced in fish raised in horizontal stripes, whereas it was maintained in fish raised surrounded by vertical lines.
This is the first time a study has shown that different environments influence the overall shape of neurons in the eye, which maps to subsequent behavior. These changes were shown in the retina, a structure at the back of the eye responsible for light detection and basic visual processing.
We were very surprised and excited to discover this level of experiential plasticity in our primary sensory organ, the retina. Neither humans nor fish are born with fully developed eyes or brains. Although many neurons are physically present, they are further refined through a process known as plasticity before adulthood. Classically, the retina has been depicted as “hardware,” and refinement was previously thought to occur primarily within highly adaptive parts of the brain, such as the cerebral cortex.
Robert Hinges, senior author of the study and Professor of Developmental Neurobiology at the London Institute of Psychiatry, Psychology and Neuroscience (IoPPN)
This study adds to the growing body of evidence that the retina preprocesses visual scenes before passing them on to the rest of the brain for further processing. This is the first study to show that this preprocessing is dependent on the retina and the visual environment in which the fish develops.
To understand whether environment influences eye development, researchers placed fish in horizontal or vertical striped environments for the first five days of life. Stripes are very prominent visual features that all animals use to understand what they see.
“People actually use horizontal and vertical features to understand more complex images, like faces. The nose is a strong vertical line, and the eyebrows are a sharp horizontal line,” Professor Hinges explains.
Half of all fish grew up in a world full of horizontal stripes. The other half experienced a world of only vertical lines. The researchers used a microscope to image neurons in the retina and found that the two groups of fish had differently shaped neurons in their retinas. The neural activity sent from the eye to the rest of the brain within the retina was also biased toward the striped patterns the fish saw during their first few days of life.
“This has the surprising potential to suggest that where we grow up influences the way we see the world,” commented Professor Hinges. “This is consistent with human studies that have shown that people who grow up in different visual environments perceive optical illusions differently. What was not known is that these changes are driven, at least in part, by changes in the early stages of visual processing, namely in the retina.”
The scientists tested whether these changes in the retina affected the fish’s behavior five days later. This behavioral test exploits the zebrafish’s innate preference to orient towards stripes parallel to its body, which relies on its ability to discriminate between different orientations of the stripes.
Using a virtual reality system that tracks the occurrence of movement, the fish were given the choice of heading in a direction parallel to the stripes or perpendicular to them. Zebrafish raised in a horizontal world failed to show this innate preference for parallel stripes, acting as if horizontal and vertical stripes were more difficult to distinguish. On the other hand, fish raised in a vertically striped world retain this preference.
“We wanted to explore how these changes occurring in the eyes affect the actual behavior of the fish,” explains the study’s lead author, Dr. Phoebe Reynolds, who carried out the research as part of her PhD at King’s University. “To do this, we developed a new behavioral test in virtual reality that shows that fish prefer lines in a certain direction. This allowed us to test whether the fish’s innate preferences are influenced by the environment in which they are raised.”
“The design of the tracking device and the behavioral paradigm were inspired by observations of structural and functional changes in the retina. It was completely unknown whether these features also influenced the ability to distinguish between stripes during behavior. We were therefore very surprised to find that the animal’s housing conditions actually had a significant effect on performance,” says Professor Armin Bahr of the Center for Advanced Research in Group Behavior at the University of Konstanz, who led the behavioral experiment. Study.
Using genetic manipulation, researchers were able to identify the contribution of retinal plasticity to this behavior. Without the effects of retinal plasticity, fish in both environments behaved similarly. This shows that biological changes in the eye determine the fish’s behavior.
This research was primarily funded by the Medical Research Council (MRC), the Leverhulme Trust, the Biotechnology and Biological Sciences Research Council, and the Emmy Noether Programme.
Dr. Phoebe Reynolds is currently a postdoctoral researcher at the Friedrich Miescher Institute for Biomedical Research in Basel, Switzerland.
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Reference magazines:
Reynolds, P. others. (2026). Early visual experiences elicit cellular and functional plasticity in the retina, leading to behavioral changes. neuron. DOI: 10.1016/j.neuron.2026.05.001. https://www.cell.com/neuron/fulltext/S0896-6273(26)00372-7
