Fall is the time of year when fish such as salmon return to Michigan rivers to spawn, beginning the reproduction cycle. It also marks the start of when Department of Natural Resources employees at the state’s fish hatcheries are busy starting the egg collection process for other species of fish. These eggs are used to begin the next production cycle and to ensure that quality brood stock is available to produce more fish in the future.

Sportfishing is a multi-billion-dollar-a-year industry in Michigan. Approximately 40 percent of all recreational fishing relies on stocked fish, including 70 percent of all fishing that occurs for Great Lakes trout and salmon.

At the Oden State Fish Hatchery in Alanson, work is underway to remove eggs from brood fish to begin the next production cycle for brown and rainbow trout. DNR fisheries biologists know from historical data roughly when the adult trout should be “ripe,” meaning when females are physically ready to expel eggs. They begin testing the females a week or two ahead of time to make sure the timing is accurate.

The main factor influencing the timing of spawning of captive trout broodstock is photoperiod or day length. It once was thought that water temperature played a role as well. However, this was found not to be the case when the change to constant water temperatures at the new Oden State Fish Hatchery had no impact on the timing of when the adults “ripened up.”

Egg-takes are conducted every two weeks from late September to early February, depending on the strain of fish. Oden rears three strains of brown trout including Wild Rose, Seeforellen, and Gilchrist Creek, and the Eagle Lake strain of rainbow trout. Typically, biologists start with the Wild Rose strain of brown trout in late September and the egg-take lasts seven to eight weeks. Then, they move on to other strains, such as Gilchrist Creek in November, Seeforellen at the end of December, and finally rainbow trout in late December and early January.

The day before an egg-take, Fisheries Technicians sort ripe females from the unripe females. The day of the egg-take, a team of two or three DNR hatchery employees works just on the females. One person sedates the fish, while another person holds the fish to let the third person on the team inject a small amount of compressed oxygen into the body cavity. The compressed oxygen provides just enough pressure so that the eggs flow out. These eggs are caught in a bucket and brought over to the male fish. With younger brood fish, the compressed oxygen is not necessary. Instead, the eggs are stripped by hand.

The males are tested for ripeness while the egg taking process is underway. The males also are sedated and their body cavity is gently squeezed to release a stream of milt, or sperm, into the bucket of eggs. Some water is added and the bucket sits for 30 seconds to one minute for the process of fertilization to occur. The eggs then are rinsed with water and drained to remove any organic matter and left over milt.

Once all the eggs are fertilized, they are treated with an antibiotic for disease prevention and then taken to the tank room’s incubation area. The eggs are sampled for size and measured out into the incubation trays at one-and-a-half liters (approximately 25-30,000 eggs) per tray. Once a stack of 15 trays is full, an iodine solution is added to disinfect the surface of the eggs. Ten days later, a sample of eggs is taken and covered with glacial acetic acid. This allows the crew to determine what percent of the eggs were successfully fertilized. Approximately 30 days after they were fertilized, the eggs develop to the point where you can see the eyes of the developing embryo. At this stage, the eggs are pretty tough and can withstand handling. It is at this point that the live eggs are sorted from the dead eggs or blanks. This is done either with an automatic egg picker, which utilizes an electric eye to sort live eggs from dead, or by a process known as salting. In the salting process, a salt solution is mixed up and a small amount of eggs are slowly and carefully placed into it. The live eggs are denser than the dead eggs so they sink to the bottom. This allows the technicians to skim the dead eggs off the surface. After salting, the good eggs are returned to the incubators. They then are either shipped to another facility to hatch or remain in the Oden facility’s incubators until they are ready to hatch or “pop.” With brown trout, that is usually about 60 days after they were fertilized. Rainbow trout develop a little faster. They generally start to pop around 45 days.

After the eggs hatch, the young fish spend the next three to four weeks in the incubators where they live off of their yolk sac. They then are placed into tanks where they will spend the next several months under the skillful care of the technicians and biologist.

Developing and maintaining hatchery facilities are important for a variety of reasons, including rehabilitation of threatened species, mitigation through replacement of fish lost because of natural or man-made disasters, and to produce fish needed for enjoyment and use by the state’s recreational anglers. The DNR’s hatchery system dates to the early 20th century.

“Fish hatcheries historically have played a major role in fisheries management in Michigan,” said Fisheries Division Chief Kelley Smith. “It wasn’t that long ago that Michigan’s beaches were rendered unusable by the seasonal die off of alewives. It was the salmon reared in our fish hatcheries that soon put the alewife population in check. This resulted in the development of a world-class salmon fishery with catch rates that west coast salmon fishermen never have witnessed. With the recent renovations of our state fish hatcheries, our fish culture facilities are poised to serve Michigan’s anglers well into the future.”

In the 1870s, fish populations in the Great Lakes and inland waters were disappearing due to habitat destruction, dam construction, over-harvest and pollution. Early logging practices in Michigan destroyed streams. There was little regulation and enforcement into the early 1900s concerning the taking of game and fish. This led to the loss of many fish and game species and the collapse of many populations, such as lake herring. Unregulated fishing of lake herring caused the population to collapse by 1926.

Hatcheries were the only technique available to fisheries managers at the time to stem the loss of rapidly diminishing fish populations. Today, the work of those pioneers is still seen, but the science behind it is more in-depth. Genetically diverse sources of wild and captive brood stock are kept for species and strains of fish. The species and strains of fish are kept in waters that match where the fish will be stocked. Parent selection and spawning are shaped to avoid inbreeding, which prevents the loss of genetic diversity.

Fish culture is a blend of science and art. There is no question that the science is becoming more and more refined, but there is no substitute for the trained eye of a well seasoned fish culturist. Michigan’s fish hatchery system consistently has led the nation in fish culture developments. Each facility consists of a staff including a biologist, several technicians and a well-trained, highly skilled maintenance crew that tends to the complex physical plant that makes up each hatchery.

Fish are acquired, reared, checked for health concerns and then distributed to the Great Lakes and inland waters of Michigan by the DNR hatchery system. The result is a sport fishery that draws enthusiasts from all over the state and country to Michigan’s waters. The economic impact of fishing in Michigan is significant, and the state hatchery system plays a key role in its success.

The state’s six hatcheries are open to the public, and most provide guided tours and educational programs. To learn more about the hatcheries, visit the DNR Web site at www.michigan.gov/dnr and click on the Fishing section.