A fresh start isn’t just for people. New research suggests exercise may work for fish, too.

North Carolina uses hatchery programs to supplement fish populations, such as trout in the mountains and striped bass in coastal waters and estuaries. Research that informs the survival and performance of hatchery-raised fish could translate into stronger fisheries and more reliable fishing opportunities across the state.

Research Need

Each year, hatcheries release millions of fish to help rebuild depleted fisheries. While these programs can increase the numbers of fish, hatchery-raised fish often struggle after release into the wild. 

Compared to wild fish, hatchery-raised fish may have trouble navigating their environment, judging danger, and interacting with other fish. These challenges can reduce their ability to find food, avoid predators, and survive after release.

Previous studies show that exercise plays an important role in brain development and learning for many animals, including fish. For hatchery fish, increased swimming activity during rearing may help improve brain function and better prepare them for life in natural waters. 

However, scientists still know little about how long-term exercise at different intensities affects fish behavior and brain development. To address this gap, researchers asked a simple question: Can exercise training improve learning and brain development in fish raised for release into the wild?

What Did They Study?

The study focused on black seabream, a similar species to red porgy and an economically important coastal fish found in China, Japan, and Korea. Overfishing has reduced wild populations of the species, leading to hatchery-based release programs since the 1970s. Despite these efforts, survival after release remains low.

Researchers raised young black seabream under different water flow conditions that forced the fish to swim continuously. Fish experienced water speeds equivalent to swimming 1, 2, or 4 body lengths per second, while a control group was raised in nearly still water.

After the training period, scientists tested fish behavior and learning using exercises and mazes that measured problem-solving ability. They also examined fish brains to count the number of brain cells in regions linked to learning and movement.

What Did They Find?

Fish that swam during rearing performed better than fish raised in still water. The greatest improvements occurred in fish exposed to moderate exercise (swimming at about two body lengths per second).

These fish solved a maze more quickly and showed behaviors more similar to wild fish when placed in new environments. Scientists also found that moderately exercised fish had more brain cells packed into key areas of the brain. Having more brain cells in these regions supports learning, memory, and the ability to respond to environmental challenges.

Fish exposed to the highest water speeds did not show the same benefits, suggesting that too much exercise may be stressful and less effective.

So What?

Stock enhancement programs often focus on producing and releasing large numbers of fish. This study shows that fish quality matters, not just quantity.

Adding moderate water flow to hatchery tanks could help produce fish with stronger learning abilities and more developed brains. These traits may improve a fish’s chances of finding food, avoiding predators, and surviving after release. 

This study was limited in the number of fish it included, but as fisheries managers look for ways to improve the success of release programs, exercise-based rearing could offer a simple and practical tool to give hatchery fish a better start in the wild. More testing could help confirm these preliminary results.

Reading

Wang, Y., Tian, M., Guo, H., Näslund, J., Wang, Y., Ru, J., Qi, Y., & Tian, K. (2025). Boosting brains: Exercise enhances cognition and neurone density in a fish reared for release into nature. Animal Behaviour, 228, 123313. doi.org/10.1016/j.anbehav.2025.123313.

Funding was provided by Natural Science Foundation of National Natural Science Foundation of China (32102755), Natural Science Foundation of Zhejiang Province (LGN22C190015), Research Program of Bureau of Science and Technology of Zhoushan (2021C21012), the Fundamental Research Funds for Zhejiang Provincial Universities and Research Institutes (2024J001-2) and Zhejiang Ocean University Student Research Training Program (2024-A-018).

Lead photo: Feeding fish at the Bozeman National Fish Hatchery. Credit: USFWS.

The text from Hook, Line & Science is available to reprint and republish at no cost, but only in its entirety and with this attribution: Hook, Line & Science, courtesy of Scott Baker and Sara Mirabilio, North Carolina Sea Grant.