Dolly Varden Trout Guts Quadruple During Yearly Gorging Session

If fish had eating competitions, there's no doubt that the Dolly Varden trout would win. Researchers have recently discovered that this fish can expand its gut up to four times its original size in order to gorge on a yearly feast.

The fish itself is large and silvery and can grow up to two feet in length. Despite its name, the "trout" is actually a char, and can be found in states that range from Washington to Alaska. Although many can be found in lakes and rivers, the Dolly Varden can also travel between both salt and fresh water--like salmon.

Once a year, these char partake in a massive feast. They lurk in the depths of rivers, waiting for salmon to spawn. When the female salmon dig out their nests in the riverbed, they disturb unhatched eggs from previous spawns. The Dolly Varden trout then swoop in, eating as much as a half-pound of salmon eggs per day.

All of this eating takes its toll, though. In comparison to other months, the Dolly Varden look positively bloated. In order to understand exactly what happens, though, the researchers examined these fish in Alaska's Alec River in the Chignik Lake watershed. Surprisingly, they found that these fish can actually change the size of their digestive tracts during this feasting period by adding new gut tissue.

"The fact that these fish can change the size of their organs to change how much energy they need just to live is a really novel thing," said Morgan Bond, one of the researchers, in an interview with LiveScience.

So what do these fish feed on when they're not gorging on salmon eggs? Apparently not much. Previously, researchers believed that the Dolly Varden had a secondary food source in the freshwater. Yet they were eventually able to determine that the fish just weren't eating much for the 10 to 11 months that the salmon weren't spawning. Instead, they fasted to the brink of death, their body sizes changing drastically.

These particular findings have important implications for conservation efforts. They show how reliant the species is on salmon populations. Unfortunately, salmon are severely depleted in the lower 48 states. If populations continue to decline, it could create a domino effect which impacts several other species.

"Wild salmon runs have been dramatically reduced across much of the lower 48 states and often are replaced with hatchery fish," said Jonathan Armstrong, one of the researchers, in a press release. "When salmon are spawned in hatcheries, bull trout--which are threatened in the Pacific Northwest--as well as juvenile coho salmon and other species of concern to conservationists no longer have the opportunity to feed on salmon eggs, which are an incredible food source."

The findings are published in the Journal of Animal Ecology.