Some Alaskan Trout Use Flexible Guts for the Ultimate Binge Diet

Mar. 20, 2013 — Imagine having a daylong Thanksgiving feast every day for a month, then, only pauper's rations the rest of the year. University of Washington researchers have discovered Dolly Varden, a kind of trout, eating just that way in Alaska's Chignik Lake watershed.

Organs such as the stomach and intestines in the Dolly Varden doubled to quadrupled in size when eggs from spawning sockeye salmon became available each August, the researchers found. They were like vacuums sucking up the eggs and nipping at the flesh of spawned-out salmon carcasses.

Brightly colored sockeye salmon surge

by as a Dolly Varden waits its chance

to binge on salmon eggs. 

(Credit: J Armstrong/U of Washington)

Then, once the pulse of eggs and spawning salmon ceased, the guts shrank and the fish lived for nearly a year off the reserves they'd built up because there is little else to eat.

Certain snakes, birds about to migrate and Atlantic cod in the laboratory are known to grow and shrink their digestive track in response to gorging, but this is the first time researchers have documented wild fish doing so, according to Jonathan Armstrong and Morgan Bond, UW doctoral students in aquatic and fishery sciences when the work was conducted. They are the authors of a paper in the Journal of Animal Ecology published online March 20.

Dolly Varden, bull trout and brook trout are among the North American members of the char family, part of the larger trout and salmon lineage. These particular Dolly Varden live where insects and other prey are scarce because of the long, cold winters. The fish can't do without the yearly egg "subsidy." Survival depends on there being lots of returning salmon, spawning naturally.

Continued:  http://www.sciencedaily.com/releases/2013/03/130320133227.htm