Spawning Trout

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.

Authors
Top