When researchers moved medaka—a fish commonly used in experiments—out of the lab and into more natural conditions, their reproductive clock shifted by hours, suggesting that laboratory findings may not fully capture their natural reproductive timing.

Research using model organisms requires an understanding of their behavior and physiology in natural environments in order to accurately interpret experimental results. Medaka are widely used as a model organism in biological research because they are easy to maintain and spawn frequently.

However, most previous studies on medaka have been conducted under laboratory conditions, leading to concerns about how well these carefully controlled experiments reflect how medaka live and reproduce in the wild.

An Osaka Metropolitan University (OMU) research group has been actively researching these differences. They previously found that medaka spawn late at night, which was different to what was observed in lab animals at the time.

Specially Appointed Assistant Professor Yuki Kondo and Professor Satoshi Awata at the Graduate School of Science at OMU were interested in whether any other reproductive behaviors were different between wild and laboratory conditions, especially the timing of ovulation—the process that leads to spawning.

When the researchers compared the timing of ovulation in medaka under laboratory conditions with those in tanks placed outdoors, they found that medaka kept in the semi-natural conditions ovulated approximately 3.5 hours earlier.

“Because we used the same strain of medaka in both environments, the difference in the timing of ovulation is likely attributable to differences in rearing conditions,” Dr. Kondo said. “In laboratory settings, artificial lighting is switched on and off abruptly, whereas in natural environments light levels change gradually at dawn and dusk. In addition, water temperature fluctuates on a daily basis outdoors. These environmental differences may contribute to the observed shift in ovulation timing.”

Their findings have important implications in research, as many biological discoveries are based on model organisms in controlled labs. The study shows that these results may not fully translate to natural conditions and that timing-dependent processes, like reproduction, are especially vulnerable.

“This study highlights the challenge of generalizing findings from animal experiments based solely on laboratory results,” Professor Awata concluded.

“Going forward, it will be important to identify the environmental factors that cause differences in behavior and ovulation timing between laboratory and natural settings,” he continued. “It is important to clarify how these factors regulate the timing of ovulation.”

The findings were published in Royal Society Open Science.

Conflict of interest declaration
The researchers declare they have no competing interests.

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