Researchers in the Netherlands have found that short-term periods of stress can lead to activation of the immune system in zebrafish. 

Stress is associated with negative health effects, particularly when chronic, as it can weaken immune defences and increase susceptibility to disease. However, scientists have long suspected that short-term stress may play a different role. 

Researchers from Radboud University used zebrafish for this because their stress hormone system closely resembles that of humans, and immune responses can be tracked visually. The team applied a short, non-harmful stress stimulus to zebrafish and observed that it brought immune cells closer to the skin, preparing them to protect the fish.  

Marcell Schaaf from Radboud and lead author on the study published on Molecular Psychiatry highlighted: “Short-term stress actually activates the immune system, whereas we know that long-term stress weakens it. We also saw a tipping point: if the period of stress lasted longer than two hours, the stress didn’t stimulate the immune system anymore, but suppressed it.” 

Future research may explore how this balance applies to other species, including humans.