Rainbow trout attract thousands of anglers to streams and community lakes where approximately 375,000 catchable-sized trout are stocked each year.
A rainbow trout’s journey to become catchable-sized stocked trout starts about 15 months before stocking. All trout broodstock are raised at the Manchester Fish Hatchery. Averaging 4-to 7 pounds, a broodstock trout’s primary purpose is to produce eggs. Thousands of visitors enjoy feeding these fish while they are in the hatchery ponds each year.
Prior to the spawn, hatchery staff seine the pond and move the trout to raceways to be sorted. Two-year-old trout are separated from three-year-old trout and males are separated from females. The fish are held separately so spawning can be completed in a controlled environment at the hatchery.
Every 10 to 13 days, the three-year-old females are anesthetized in a tank in the exterior raceway and checked for ripeness.
“Without anesthetizing the fish, the process turns into a wrestling match potentially injuring the trout and hatchery staff alike,” said Dan Rosauer, fisheries biologist at the Iowa Department of Natural Resources Manchester Fish Hatchery.
All ripe females and the necessary number of males are transferred to tanks inside the hatchery building. Two females and three males are anesthetized at a time. The females are held over a net to collect the eggs by gently pressing on their bellies. The eggs are placed into a dry fertilizing pan and the milt is added to the eggs. Both the eggs and milt are activated by adding water to the pan. After activation, the mixture is gently stirred for thirty seconds before milt from the final male is added to ensure sufficient fertilization. After fertilization, the eggs are rinsed and placed in incubators to develop for the next 30-36 days.
Approximately 750,000 rainbow trout eggs are incubated and hatched at the Manchester Fish Hatchery each year. The resulting fry are cared for until they reach 3-4 inches in size then stocked into streams or transferred to outdoor raceways at the Manchester, Big Spring or Chuck Gipp Decorah fish hatcheries.
The fingerlings are raised to 11-12 inch catchable-size before being stocked for anglers to enjoy. Find more information about Iowa trout streams and tips for trout fishing on the DNR website at www.iowadnr.gov/trout.