On rivers and streams in salmon country, Halloween brings horrors that rival The Walking Dead.
Terrifying “zombie fish” swim these cold, shallow waters, offering a spooky sight that hard-core fishermen know all too well. And while this sounds like fake news, it’s anything but.
If you want to know about these real-life zombie fish, keep reading!
“Zombie Fish:” Dying to Reproduce
Pacific salmon of all six species begin their lives as tiny fry in freshwater rivers and streams, slowly maturing in these habitats as they gain size and strength.
As they near maturity, they’ll move toward the sea, where they’ll undergo physical changes that allow them to thrive in saltwater. Once ready, they’ll move out into the ocean, where they spend the majority of their lives.
Driven by a carefully-timed biological clock, salmon know when it’s time to spawn, and these mature fish are drawn back to the waters where they themselves hatched, led by signals that scientists are only just beginning to understand.
They don’t find a stream like the one where they were hatched; they find the stream where they spawned.
As they begin this arduous journey, they’ll stop feeding entirely, fighting their way past hungry bears, skilled anglers, and rapids that are all but impassable. Burning their fat stores as they swim, they fight upstream against all odds until they reach the place where they were spawned.
Spawning salmon return to the exact location they were themselves spawned.
Once there, it’s time for them to spawn in turn, and they come together to release eggs and sperm in an orgy of excitement.
But Pacific salmon spawn only once in their lives, and this season of birth triggers their death.
Doomed to die once they've ensured the life of the next generation, post-spawn salmon start decaying rapidly, showing what scientists call senescence “from the time they start breeding until the time they die several weeks later.”
The salmon are literally dying while swimming, their bodies withering and their organs failing. Even their immune systems shut down, allowing bacteria overgrowth and literal decay.
That process leads to a kind of living death that can last for as long as two weeks.
This post-spawn salmon provides the nutrients its fry need to thrive.
This final sacrifice is a carefully choreographed transition of life into death followed by rebirth and life again. As you probably know, the seasonal salmon run provides food for wildlife of all kinds, but the salmon’s real gift is to its fry.
Salmon fry feed on aquatic invertebrates that depend on “zombie fish.”
As the salmon die and decompose after breeding, they feed everything from bacteria and microbes to insect larvae of all kinds. Shortly, their fry will hatch and begin feeding, and this abundant food source - timed just right - will have ensured lots of healthy, fat insects for them to eat as they begin their life cycle.
Without “zombie salmon,” the next generation wouldn’t have the nutrient-dense diet it needs to grow quickly and begin the cycle anew.