Spawning Trout

By Joe Wilkinson

Iowa Department of Natural Resources

Future fishing sits in trays and raceways, in the DNR trout hatchery near Manchester this winter. With the final spawning of rainbow trout, the stocking class of 2015 is taking shape.

Already, tiny brook trout and brown trout move like dark clouds in the indoor raceways…aware of any movement as they wait for aluminum feeders to clang open. Every 20 minutes, the timer hits and commercial feed drops to feed them. The first of the season’s rainbow trout are now sac fry. They and the late spawned eggs sit under a constant, cold stream of spring water. This hatchery, originally a federal facility, was sited here in the late 1800s because of the volume and quality of the water.

“Typically, we rear between 300-350,000 rainbow trout and 50-75,000 brook trout to catchable size annually; with adjustments for fingerling availability, changes in stream management and weather,” explains Manchester hatchery manager Dave Marolf. “We also produce between 125,000-175,000 brown trout fingerlings to stock as two-inch fish in May into watersheds that do not already have natural reproduction. That supplements reproduction of browns, in about half of the spring-fed watersheds in northeast Iowa, which do not have to be stocked.”

So, about once a week from October through January, it’s time to spawn fish. Late in the rotation now, that means netting 6 to 8 pound ‘ripe’ female rainbows. The brood fish are stripped by hand, as workers gently but firmly rub bellies to steer streams of bright orange eggs—up to 4,000 to 6,000 per fish-- into a net and then plastic bowl.

With similar motions, sperm is extracted from two smaller males—to provide genetic diversity—and mixed into the egg mass. Stirring for 30 seconds with a turkey feather produces 95-99 percent fertilization…dozens of times better than leaving it up to Nature in the stream.

Sometimes, the week-to-week chore turns into a field trip destination, for potential biologists-in-training.

“Pretty interesting. I’ve never held a trout that big before; really slimy, really small scales. It was difficult to grab on to the tail and support her head,” reports Zach Hall of Council Bluffs--a student in Dr. James W. Demastes’ Field Zoology class.

Each of a dozen junior or senior University of Northern Iowa biology or education majors pulled on a raincoat and elbow-length rubber gloves to coax a stream of eggs into the waiting net.

“We just started our fish unit. They have been studying specimens for about a week. This gives them a chance to go out and look at animals in the middle of winter,” notes Demastes.

The hands-on approach was overseen by hatchery technician Randy Mack.

“Once fertilized, eggs go into trays; then to the incubator unit for 30-45 days (depending on water temperature) before they hatch,” says Mack. “From there, it is four or five months indoors before being moved to the big raceways outside…or at the Decorah or Elkader rearing stations.”

It takes about a year and a half for them to reach 11-inch, half-pound catchable size. Fish spawned this fall and winter will be in the stocking class of 2015. Come this spring, fish hatched last winter will be on the trucks.

Up to 40,000 of us go after trout each year. That number has grown, with the expansion of Iowa’s cold weather urban trout program. Unable to survive in warm weather, trout can make it through the winter in 17 small lakes, ponds or renovated quarries throughout the state. Some of the new anglers enjoy the new pastime locally…while others hear the call to head to the bluffs of Trout Country in northeast Iowa.

Visit the DNR Trout fishing web page for more information about trout streams, trout stocking schedules, fishing for trout, and trout hatcheries.