The life cycle of salmon is one of nature’s most incredible stories. Born in freshwater streams and rivers, they make an epic journey out to sea where they spend their adult years, before returning to their exact place of birth to spawn and die.
It’s this final spawning stage that gives rise to a fascinating phenomenon – salmon that appear “undead” with decaying, decomposing bodies while still alive. Often referred to as zombie salmon their disturbing appearance has captivated biologists and outdoor enthusiasts alike.
In this article we’ll take a deep dive into the zombie salmon mystery and find out if salmon truly decompose before death.
A Salmon’s Lifecycle Culminates in Reproduction and Death
- Salmon are anadromous fish, meaning they are born in freshwater but spend their adult phase in the ocean.
- When it’s time to spawn, they will swim enormous distances back to their natal streams and rivers.
- Spawning requires huge amounts of energy as they undertake strenuous upstream migration while undergoing bodily changes to enable reproduction.
- Most salmon species spawn only once before rapidly deteriorating and dying soon after.
- Some key Pacific salmon species like chinook, sockeye, coho, chum, and pink salmon all share this single spawning lifestyle and dramatic end.
Salmon Undergo Extreme Physical Changes Post-Spawning
After the exhausting spawning process, salmon are utterly depleted, unable to feed or swim. Without any energy reserves left, their bodies deteriorate extremely quickly.
- Skin becomes covered in lesions, fungal growths, and white spots.
- Fins fray and tails deteriorate.
- Muscles atrophy leading to a distorted body shape.
- Scales and mucus coat fall off leaving them vulnerable to infection.
- They appear discolored and bloody as skin pigments change.
In this deteriorated state, spawned out salmon can be seen drifting along erratically near the water’s surface, flashing their zombie-esque look before their imminent death.
The “Zombie” Nickname Reflects Appearance, Not Actual Decomposition
While their decaying exterior gives them a zombie moniker, salmon do not fully decompose until after death. True decomposition involves cellular breakdown and invasion of bacteria and fungi into tissues, which cannot occur in a living animal.
Some key reasons spawned out salmon do not decompose while alive:
- Biological processes – Organs still function to prevent systemic infection/invasion.
- Rigor mortis – Muscle stiffening only occurs post-mortem.
- Digestive breakdown – Digestive enzymes leak out after death but not before.
The outer deterioration is shocking but it’s not the true decomposition seen in dead bodies. So zombie salmon are not actually in a state of decay while they are still living, despite outward appearances.
What Causes the Salmon to Deteriorate Before Death?
Many complex factors contribute to the salmon’s pre-death deterioration:
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Expended energy – They’ve used up every bit of their metabolic reserves after the strenuous spawning migration. With their energy depleted, their bodies waste away.
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Hormonal changes – Reproduction triggers extreme hormonal shifts which lead to organ and tissue breakdown.
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Lack of feeding – No longer eating, nutritional resources are fully exhausted accelerating wasting.
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Toxins – Metabolic wastes and toxins build up as liver function declines.
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Osmotic stress – Transitioning from saltwater to freshwater environments creates osmotic stress on cells.
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Immune decline – A weakened immune system allows pathogens and fungi to invade their bodies.
After Death, the Full Decomposition Process Begins
Once spawned-out salmon actually die, decomposition progresses rapidly:
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Bacteria, fungi and other organisms proliferate throughout the body.
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Gas buildup causes bloating and buoyancy that can return some carcasses out to sea.
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Tissues liquefy as cellular structures disintegrate.
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Scavengers consume and disperse the remains.
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Nutrients are recycled to enrich the ecosystem.
Why Do Salmon Evolve to Deteriorate So Severely?
This dramatic pre-death deterioration serves key evolutionary purposes for salmon species:
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It maximizes their reproductive fitness by diverting all energy to spawning rather than self-maintenance.
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It eliminates competition for resources between generations.
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It provides nourishment for offspring and aquatic life as carcasses decompose.
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This severe process has proven to be an extremely successful evolutionary strategy over time.
The Salmon Lifecycle Continues After Death
While the deterioration phase seems tragic, it enables salmon to achieve their sole mission – passing on their genes by reproducing.
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Eggs laid in gravel nests hatch into juvenile salmon called fry.
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The fry grow and travel out to sea to repeat the salmon lifecycle.
So in their death, salmon provide sustenance to continue their offspring’s survival in a never-ending cycle.
Key Takeaways on Zombie Salmon
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Spawned-out salmon exhibit extremely decayed bodies before death – leading to their “zombie” nickname.
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They do not yet show true decomposition while alive – just severe external deterioration.
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This pre-death wasting is caused by total energy expenditure, hormonal shifts, osmotic stress, toxins, and immune decline.
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Full decomposition begins only after death when microorganisms proliferate through their bodies.
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Their dramatic end has evolved to maximize reproduction and nourish the next salmon generation.
So while horrifying to us, the zombie salmon play a key role in this iconic fish’s natural lifecycle and survival as a species. Their decomposition after death offers one final gift – nutrients to sustain their own offspring and aquatic ecosystems.
Next time you see these gnarly spawned-out salmon, remember they still have some living yet to do before they can fully transform into the dead and decomposing zombies they appear to be!
Can you eat a zombie salmon?
If you eat a zombie salmon, you won’t turn into a zombie yourself. You just might not find it very tasty. You know that fat that makes salmon so delicious? It was burned as energy during the fish’s long journey home.
Also, there’s a fine line between a zombie salmon and a dead salmon, which can make you sick. Dead fish will have a higher amount of dangerous bacteria than those still alive with healthy immune systems.
When the life cycle is over
After juvenile salmon leave their natal lakes and streams for a life at sea, their magnetic sense of direction leads them back. These adults swim upstream to reproduce, a process called spawning. Once they have released and fertilized their eggs, it only takes a few weeks for those salmon to die.
During those weeks, those fish become shadows of their former selves. Their bodies begin to shut down and actually rot. Hearts, arteries, and muscles fall apart. Digestive organs shrivel up. The skin loses its bright, colorful hues.
How Salmon Evolved to Die After Spawning
FAQ
FAQ
Do salmon rot while still alive?
Some deteriorating salmon are still alive, but their bodies have already begun the process of rotting, and these deteriorating salmon are sometimes …
What happens to all the dead salmon?
Life After Death
Depending where the carcasses lay, they’re fodder for fly larvae and aquatic grazers like caddisflies. In an odd twist of fate, these same insects will feed the new generation of salmon incubating beneath the gravel. Many carcasses, snagged by fallen trees, stay put or don’t stray far.
Do all salmon die after they spawn?
No, not all salmon die immediately after spawning.
Do salmon bones decompose?
Fish bone is adding excellent nutrients to the pile! I don’t put any bones in my compost, but they will break down, especially small fish bones. Mostly yes but depending on what kind of fish maybe not the skull or vertebrae. The ribs and fin rays wouldn’t be an issue.