Explaining the zombie-like transformation of Utah’s kokanee salmon

SALT LAKE CITY ( ABC4 ) — Kokanee salmon — a popular sport fish in Utah — undergo extreme changes in the fall, including turning red and growing elongated jaws and teeth, before eventually decomposing and dying.

Local Utah expert Trina Hedrick with the Division of Wildlife Resources spoke with ABC4 about what drives this transformation and how it affects Utah’s ecosystem.

An ‘extreme’ transformation

Trina Hedrick, the cold water sport fish coordinator for the state of Utah, described the adaptation as “wild” and “extreme.”

“They go from being silvery shiny fish with scales to being bright red. The males get a big hump on their back, they get a bigger, more like crazy defined jaw, teeth,” she said.

Hedrick said that kokanee salmon in their third or fourth year of life will reabsorb their scales into their body which exposes the red pigmentation of their skin. The coloring comes from their diet of zooplankton, much like how a flamingo gets its color.

In addition to the reabsorption of their scales, males will also grow a hump and their jaw will elongate. This is the first step of a transformation that eventually leads them to their death.

A deadly commitment

Hedrick said the purpose of the changes is for reproduction, as the fish return to the streams from the reservoirs to spawn from September to October. The teeth and hump help the male fish claim space to increase their chances to pass their genes on.

While they can be aggressive during this time, Hedrick said their aggression is contained to members of their own species as they are singularly focused on reproducing. The fish also begin to act recklessly by swimming in shallow waters without their scales to camouflage them.

“They will run up very shallow streams, be very exposed potentially to avian predators,” Hedrick said. “Things that, you know, fish wouldn’t normally do, just because that drive to reproduce is so strong.”

Once the transformation starts, the fish do not have a lot of time to spawn as their bodies start putting everything into egg production and other reproductive needs. Hedrick says this leads to a sort of “decomposing” process.

For example, she said parts of the fish’s skin might start to sag off as any scrape or injury they receive will no longer heal.

“Sometimes it does seem like they’re zombie fish in a way,” Hedrick said.

Prior to her current position, Hedrick worked as a manager and was assisting at the Sheep Creek spawn when she saw the inside of a decomposing kokanee for the first time. She said they had to cut one of the fish open and found that the fish “literally had nothing except eggs” inside of it.

“I’ve been so horrified in a way, to be honest, and then also just impressed. Like that is commitment, right?” she said. “I know they’re maybe not able to stick around and care for their young, but that is the extreme caring for your young, really, when you think about it.”

Their deaths ‘feed their young’

Kokanee salmon are originally from the Alaska area, which Hedrick said has pretty sterile, non-productive systems — meaning there is not a lot of food for the fish. She said the salmon are born in streams and have a long journey to the ocean.

“They just evolved to provide that productivity for their young. So that’s why they die. Their nutrients that are in their body then are released to the system and can produce kind of a food base for their young,” Hedrick explained.

The bodies of the adult fish break down and provide nutrients for algae spores, breeding plant production, and zooplankton blooms.

“It’s kind of a cool thing that has evolved over probably millions of years for these adults to essentially feed their young in a way, it’s just not the way you might think of,” she said.

Kokanee salmon in Utah

While Utah’s water systems are more productive than Alaska’s and don’t necessarily need the parents to die and break down, Hedrick said the extra nutrients do help the water systems here.

She said that while the kokanee salmon are not native to Utah, they are foragers and essentially only feed on zooplankton. The kokanee also serve as a “prey base” for predatory fish species here, such as lake trout and splake.

Hedrick said the species is an important sport fish in Utah as they can be a challenge to catch and taste delicious.

“They definitely make the anglers happy,” she said. “People love to fish for them, and so we work really hard to try and make sure that we have good kokanee fisheries for folks.”

For information on where you can find kokanee fish and seasonal restrictions on kokanee salmon fishing, view ABC4’s previous article .

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