Do Salmon Decompose While Alive? Examining the “Zombie” Salmon Phenomenon

Salmon have an incredible and unique life cycle that takes them from freshwater streams to the ocean and back again to spawn. After spawning, salmon undergo rapid deterioration, leading some to ask – can salmon decompose while still alive? This strange “zombie” salmon phenomenon has fascinated biologists and outdoor enthusiasts alike.

In this article, we’ll explore what happens to salmon after spawning, examine whether they can decompose while alive, and shed light on this intriguing phase of the salmon life cycle.

Salmon Deterioration Post-Spawning

• Most salmon species spawn once before dying.

• Spawning requires tremendous energy expenditure for migration, physiological changes, and sexual maturation.

• Salmon are tired and worn out after spawning because they’ve used up all of their energy.

• No longer able to feed or actively swim, salmon deteriorate rapidly after spawning.

• This post-spawning deterioration leads to dramatic physical changes and eventual death.

The “Zombie” Salmon

• Some spawned-out salmon exhibit extremely deteriorated bodies while still alive, earning the “zombie” nickname.

• Their skin becomes covered in lesions and fungal growths.

• White spots appear on their skin as tissues begin breaking down.

• Fins and tail may be frayed and eroded.

• Body shape becomes misshapen as muscles atrophy.

• Scales loosen and fall off as the protective mucus coat deteriorates.

• “Zombie” salmon may still be seen swimming erratically just prior to death.

Can Salmon Decompose While Alive?

While spawned-out salmon have a zombie-like appearance, they do not actually decompose while still alive. True decomposition involves the breakdown of tissues by bacteria, fungi and other organisms which invade the body after death.

• Biological processes – As long as a salmon is alive, biological processes prevent the invaded decomposition seen with dead organisms.

• Rigor mortis – Rigor mortis, or post-mortem muscle stiffening, is one of the first signs of decomposition, but this does not occur in living fish.

• Digestive breakdown – The digestive system also ceases function after death allowing intestinal bacteria to aid decomposition internally.

So while their deteriorating bodies may make salmon appear “undead,” they do not yet show the true cadaveric decomposition that requires death as a prerequisite. The zombie salmon nickname refers more to their outward appearance than actual internal decay.

What Causes the Deterioration?

• Expended energy – Salmon have used up all metabolic reserves to complete the strenuous spawning journey. With no energy left, their bodies rapidly waste away.

• Hormonal changes – Spawning triggers dramatic hormonal changes in salmon. Post-spawning hormone levels lead to tissue breakdown and organ failure.

• Suspended feeding – No longer eating or metabolizing food, nutritional resources are fully depleted. Starvation hastens the deterioration process.

• Osmotic stress – Transitioning from saltwater to freshwater environments creates osmotic stress which compromises organ function.

• Toxins – Metabolic wastes and toxins build up with reduced liver function, accelerating tissue necrosis.

• Immune decline – With their immune system weakened, opportunistic pathogens can invade the salmon’s body leading to fungal infections, lesions, and septicemia.

What Happens After Death?

Once a spawned-out salmon dies, decomposition progresses rapidly:

• Bacteria, fungi, and yeasts proliferate throughout the body.

• Digestive enzymes break down tissues from within.

• Gas buildup leads to bloating and buoyancy which can return some carcasses to the ocean.

• Flesh liquefies, losing all form and structure.

• Scavengers consume and scatter the remains.

• Nutrient recycling of the salmon’s body benefits other organisms and enriches the ecosystem.

Why Do Salmon Deteriorate So Dramatically?

Salmon have evolved this severe post-spawning deterioration for a few key reasons:

• Directs all energy to reproduction – Diverting resources to immune function and tissue maintenance would take away from the goal of maximizing reproductive output.

• Eliminates competition – Rapid death clears the way for offspring without adults competing for resources.

• Provides nourishment – Decaying carcasses offer nutrition to salmon fry and aquatic life.

• Repeated success – Dramatic post-spawning death has proven an effective evolutionary strategy, leading to the salmon’s success.

Unique Salmon Life History

• Salmon demonstrate impressive biological adaptations and physiologic changes to be able to carry out their iconic life cycle.

• They transform to survive the freshwater, ocean, and spawning phases.

• Post-spawning deterioration, while extreme, allows salmon to achieve their sole mission of passing on their genes by reproducing.

• The zombie salmon may seem like the tragic end, but their decomposing bodies enrich the waters and help continue the salmon’s legacy.

Spawned Out Salmon FAQs

Q: How long do spawned out salmon live for?

A: Most spawned out salmon survive for only a few days to two weeks after spawning. Some kelts may live a bit longer but all spawned out salmon eventually die.

Q: Can you eat zombie salmon?

A: It’s not recommended to eat deteriorated zombie salmon as the quality and safety cannot be guaranteed. The meat may contain toxins or pathogens.

Q: Why don’t salmon eat after spawning?

A: Dramatic hormonal and chemical changes prevent salmon from feeding after spawning. Digestive systems essentially shut down as reproduction becomes the sole priority.

Q: Do all Pacific salmon deteriorate and die after spawning?

A: Yes, all Pacific salmon species including Chinook, chum, coho, pink, and sockeye experience post-spawning demise. Some Atlantic salmon may spawn more than once.

Q: How does the salmon life cycle continue after the adults die?

A: Eggs laid in gravel nests hatch into juvenile salmon called fry or alevins. The fry mature and travel to the ocean to repeat the cycle as the next generation.

A Remarkable Fish

While we may recoil from their grotesque zombie-like appearance, spawned-out salmon provide an essential source of marine nutrients. Their dramatic post-reproduction deterioration and decomposition is a key part of sustaining the larger aquatic ecosystem.

So next time you see a deteriorating salmon, remember that this is a natural process that enables these amazing fish to achieve their life’s purpose. In their death, salmon give life and abundance to future generations, underscoring their integral role in nature’s profound cycles.