Hatchery fish can’t keep their looks — study links stress to asymmetry.
Wild salmon don’t just survive better than their hatchery cousins — they look better doing it.
That’s the conclusion of a new study in the Journal of Fish Biology, which found that wild salmon are more symmetrical than hatchery-reared fish. In biological terms, symmetry is a sign of low stress. In human terms, it’s the quality that makes stars like Zendaya and Harry Styles icons of beauty.
“Wild salmon are the Zendayas of the fish world,” said lead author William Perry, Postdoctoral Research Associate at Cardiff University, writing in The Conversation. “Symmetry matters.”
Hatchery fish can’t fake it
The research focused on the Saimaa salmon (Salmo salar m. sebago), a critically endangered, landlocked population in Finland that has relied on hatchery production for more than 50 years. Without hatcheries, the species would likely be extinct, after hydropower and deforestation destroyed its spawning grounds.
To test how hatchery conditions affect fish development, researchers raised salmon under four different systems:
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Standard tanks
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“Enriched” tanks with fluctuating flows and shelters
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Semi-natural stream ponds with natural prey
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Direct release into rivers as alevins
Fish were photographed from both sides and compared for symmetry. The results were striking: salmon that went straight into rivers as hatchlings retained their symmetry — the Zendayas of their species. Those kept in tanks, even for just a year, showed visible asymmetry and changes in fin and jaw size that could make them less fit in the wild.
Vogue vs. volume
Aquaculture produces more than 3 million tonnes of Atlantic salmon annually, equivalent to around 600 million fish. By contrast, fewer than two million wild salmon now return to rivers each year, prompting the IUCN to classify the species as endangered in Britain.
For conservation, that means hatcheries can sustain numbers but not necessarily quality. Stress in artificial environments appears to warp the very traits that make wild salmon effective — and, in this case, more beautiful.
The study — Stress-linked morphological change associated with rearing techniques of hatchery-reliant endemic landlocked Atlantic salmon (Salmo salar m. sebago) by Aurora Hatanpää, Hannu Huuskonen, Jorma Piironen, Raine Kortet and William Bernard Perry (DOI: 10.1111/jfb.70149) — concludes that the earlier hatchery fish are released into rivers, the better. But it also warns that hatcheries are not a substitute for restoring natural habitats.
