Farmed Fish Can Evolve at a Surprisingly Fast Rate

From an evolutionary perspective, every creature on Earth has just one objective: to survive long enough to pass on its genetic material to the next generation. In periods of scarcity or intense competition, only those individuals with a genetic edge will succeed. Such is the case with hatchery-raised fish, which scientists say are evolving with astonishing speed. The researchers published their findings in the journal Nature Communications.

Aquaculture is essential for the global food web. Fish and shellfish are bred and raised in human-controlled environments. Some, like steelhead trout (Oncorhynchus mykiss), are raised in hatcheries, released into the wild, and captured later (that’s the “wild-caught” fish you see on your menu).

"A fish hatchery is a very artificial environment that causes strong natural selection pressures," co-author Michael Blouin said in a press statement. "A concrete box with 50,000 other fish all crowded together and fed pellet food is clearly a lot different than an open stream."

Working in tandem with the Oregon Department of Fish and Wildlife, Blouin and his colleagues sequenced the DNA of both hatchery-raised and wild-origin O. mykiss specimens. As the offspring of wild trout, the hatchery-raised fish represented just a single generation’s experience with captivity.

That single generation was enough to make a huge impact on the hatchery-raised trout's DNA. The researchers found changes in 723 genes. Many of these genetic variations seem to be adaptations to the hatchery environment, where injury and illness are common.

"We observed that a large number of genes were involved in pathways related to wound healing, immunity, and metabolism, and this is consistent with the idea that the earliest stages of domestication may involve adapting to highly crowded conditions," lead author Mark Christie said in the press statement.

“We expected hatcheries to have a genetic impact," Blouin added. "However, the large amount of change we observed at the DNA level was really amazing. This was a surprising result."

The researchers say identifying these changes can highlight issues in hatchery management and may eventually lead to improvements in the way the fish are raised.