Zebrafish are often used to investigate biological processes
A natural bleach produced by the body appears to play a key role in marshalling the immune system to fight off infection and heal wounds.
US scientists, working on zebrafish, which have similar genes to humans, found a burst of hydrogen peroxide is released following a tissue injury.
This seems to be the signal for white blood cells to converge at the site of damage and begin the healing process.
The Nature study may help explain conditions such as asthma.
Asthma, obstruction in the lungs and some inflammatory gut diseases have all been linked to high levels of white blood cells.
Although zebrafish would at first appear to have nothing in common with humans, they do have similar genes and are widely used to investigate biological processes.
The researchers, from Harvard Medical School, inserted into the fish a gene that glows in the presence of hydrogen peroxide.
They discovered that when the tail fins of these fish were injured, a burst of hydrogen peroxide was released from the wound and into the surrounding tissue.
Teams of white blood cells appeared to respond to this chemical signal, arriving at the site of the wound to begin the healing process.
When the researchers blocked the ability to produce hydrogen peroxide, white blood cells failed to respond to the injury.
Researcher Professor Timothy Mitchison said: "We've known for quite some time that when the body is wounded, white blood cells show up, and it's really a spectacular piece of biology because these cells detect the wound at some distance.
"But we haven't known what they're responding to. We do know something about what summons white blood cells to areas that are chronically inflamed, but in the case of an isolated physical wound, we haven't really known what the signal is."
In the human body, hydrogen peroxide is produced primarily in three places - the lung, gut and thyroid gland.
Professor Mitchison said: "Perhaps in conditions like asthma, the lung epithelia is producing too much hydrogen peroxide because it's chronically irritated, which, if our findings translate to humans, would explain inappropriate levels of white blood cells.
"This is certainly a question worth pursuing."
Dr Leslie Knapp, of the University of Cambridge, said: "Although hydrogen peroxide is routinely used for wound cleaning and prevention of infection, some laboratory-based studies suggest that hydrogen peroxide can have a negative effect on the healing process by interfering with the activities of cells that form connective tissue.
"This new study, involving a living organism, could provide new insight on immune function and the causes of various inflammatory diseases in humans."
Dr Elaine Vickers, of the charity Asthma UK, said hydrogen peroxide levels did appear to be higher in the lungs of people with asthma, but it was not clear why.
"We welcome any research that increases our understanding of the role that hydrogen peroxide plays in the body.
"This could shed light on the causes of asthma symptoms and potentially lead to new avenues for creating future asthma treatments."