Trout Spawning Indoors

By Joe Wilkinson

Iowa Department of Natural Resources

Are there 100,000 tiny brown trout darting along the concrete raceway, inside the Manchester hatchery? Just take their word for it. The tiny, just hatched fry resemble a black wriggling cloud rolling through the water.

These brown trout were spawned in the hatchery in November. Brook trout are worked up in October. Rainbow trout eggs are taken through December and into January. From previous years, hatchery workers know about how many eggs come from females of each species and their hatch rates. That provides a handle on, for instance, how many three-inch brown trout fingerlings will be on hand to stock this spring.

In the wild, reproduction rates run well below one percent. In the labor intensive spawning and rearing world at the hatchery, survival rates clear 60 percent. The cost of doing business is covered—barely—by your $12.50 annual trout fee.

“These take about three years to get to maturity; nine or 10 inches,” outlined DNR hatchery technician Randy Mack. He had sorted and anesthetized a few dozen females already and—with hatchery manager Dan Rosauer—was now stripping eggs from them, to mix with sperm from brood males kept  on the hatchery, too. 

“Anglers like these wild, stream raised fish. They are harder to catch. They’re prettier in color. They’re just a more wild fish,” noted Mack.

Having lost some of the larger brood fish this year, workers made do with 10-inch brown trout. Though still mature, each smaller female yielded only about 400 eggs, instead of 1,500. As a result, it took more of them--and more time--to reach 2015 quotas.

Different fish, different sizes…but the process is much the same. Firmly stroking fish bellies, workers strip eggs from each fish into a fabric net, then a pan to be fertilized, mixed and poured into specially designed hatching tray. The trays sit under constant cold water from nearby Spring Branch. They hatch in 30 to 40 days, depending on the water temperature.

The brown trout used for spawning are captured wild from French Creek in Allamakee County. They are held at the hatchery, across two spawning cycles. That guarantees wild, brown trout fingerlings going back into northeast Iowa streams to grow up that way.

There is natural reproduction of brown trout in northeast Iowa’s coldwater streams. However, it does not meet the demand from trout anglers who fan out across 50 or so streams through the year.  Besides brown trout, about 100,000 brook trout…and 400,000 rainbow trout are stocked each year.

The brooks are also from wild stock; out of South Pine Creek in Winneshiek County. The rainbow trout are from two hatchery developed strains. Those two species are reared for over a year—until they are 10-to 12-inch, half pound keeper-sized fish. They tend to be more ‘angler friendly’ in the streams as about 40,000 of us pursue them—primarily from April through October.

As they grow, they go outside to larger raceways at Manchester or are trucked to rearing stations near Decorah and Elkader. As they hit stocking size, crews from all three facilities stock them in nearby streams.

The brooks and rainbows are also stocked at nearly 20 urban locations through the cold weather months.