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Guts of glory: Alaska Dolly Varden avoid migration by feasting on massive scale


University of Washington scientists studying Dolly Varden in the Chignik Lake drainage in Southwest Alaska have discovered the fish living year-round in fresh water when they should be making their annual journey to salt water looking for food. Further investigation turned up a trait that surprised the researchers -- a trait previously found in snakes and birds but unknown in wild fish.

Forget Thanksgiving: In the world of gorging, the Dolly Varden trout has humans and their holidays beat. A new study finds this trout feasts once a year, expanding its gut up to four times the usual size to make the space.

The Dolly Varden could not remain in fresh water if it weren't for the massive salmon runs in the Chignik drainage, reports Live Science.

During salmon spawning season in the late summer or early fall, the trout lurk as female salmon root in riverbeds to create nests for their eggs. All this digging turns up unhatched eggs from previous lays, which Dolly Varden view as a sumptuous feast. In the monthlong spawning season, the trout can put away a third to a half-pound of eggs each day. Eating a quarter of their body weight daily for a month is no easy task.

Remarkably, the Dolly Varden digestive tract then shrinks to decrease energy requirements and preserve the fish through the long fasting season ahead, says researcher Morgan Bond.

It's an evolutionary adaptation that could be protecting them from the predators and other hazards encountered by fish going to sea, the co-authors say.

"These are pretty large-bodied fish living in a place that is relatively nutrient poor but the egg subsidy allows the fish to remain in fresh water year after year. They don't have to go to sea," Bond said.


Read more: Trout guts balloon for yearly gorge