Wild fish grown in captivity quickly adapt to their artificial environments with big changes to DNA.
In a paper published in Nature Communications, researchers found that after only one generation, differences showed up in 736 genes compared to wild cousins.
Crowded conditions, frequent injuries and exposure to disease spur the fish to adapt with changes to immunity, wound healing and metabolism, the authors said.
Researchers have long suspected differences between wild fish and their domesticated counterparts. Fish born in hatcheries that are released into the wild reproduce at much lower rates.
The study's authors said more study of the genetic differences could help farmers improve conditions and make farmed fish closer to species found in the wild.