Spawning Day at Mokelumne River Hatchery


Spawning Day at Mokelumne River Hatchery

Normal steelhead production and how we fit into it

Mokelumne River Hatchery (MRH) is located near Clements, CA just downstream of Camanche Reservoir. Here, they raise steelhead and Chinook salmon for release. Because natural populations of these salmonids are declining, adding hatchery fish (hatchery fish have clipped adipose fins) to our rivers allows there to be more fish filling those ecological roles as well as offering people the opportunity to fish for Chinook and steelhead. Hatchery steelhead production begins in late December and continues to the end of January. MRH has agreed to collaborate with us so we could ask questions about epigenetic effects of life history and Omy05, a chromosomal region strongly associated with migration. Normal production features staff spawning steelhead that are ready to go but for our experiment, we need to create specific crosses. Thankfully, MRH has helped us to slightly adapt parts of the protocol so we could create these crosses.


Broodstock prep

Nonlethal fin clipping: allows us to genotype broodstock so we can make informed crosses based on our genes of interest

Before spawning began in December, we drove up to MRH from Santa Cruz so we could take nonlethal fin clips of the broodstock fish and tag them. Fin clips allow us to genotype our fish for Omy05 so we can make crosses based on what kind of families we want to create. The tags allow us to identify the fish and their information on spawning day.


Fish are gently anesthetized

Hatchery staff anesthetize fish prior to spawning to decrease stress. They recover afterwards in clean water unharmed.

Unlike other salmonids, steelhead can spawn multiple times in a lifetime. Hatchery staff take extra care to decrease stress on fish to ensure that they will be able to reproduce in subsequent years. Fish are anesthetized before spawning and eggs are removed using air pressure instead of manual stripping. After spawning, fish are returned to one of the hatchery raceways, where they wake up and go about their day. When spawning Chinook, the process is extremely gorey because Chinook salmon are semelparous, meaning that they die after a single reproduction event. This is beneficial for their offspring because the corpses of the adult salmon nourish the stream where their eggs are developing. For hatcheries, this means that fish are killed immediately and gametes are stripped from their bodies instead of taking the time to anesthetize them like with steelhead.


Eggs are collected in bowls for fertilization

Milt is added from male fish by hatchery staff

Air pressure gently removes eggs from female steelhead into a dry bowl. Milt is then added from a male by hatchery staff. This process, called dry spawning, ensures successful reproduction by not activating the eggs with water until milt is added. For our crosses, we collect gametes in separate tupperware containers and store them on ice so we can make specific crosses as the day goes on without distracting from steelhead production.


Because keeping families separate benefits our research, crosses generated for this project are kept in separate rinsing buckets before entering the divided tray incubators.

Upright incubators

Embryos develop in these stacks until after hatching

Embryos develop in these vertical upright incubators that allow for clean water to constantly flush over eggs like what happens when wild salmonids develop. This prevents the spread of fungus from dead eggs to healthy eggs. Hatchery staff check drawers and remove dead eggs to prevent mass mortalities. Embryos hatch into alevin and stay in these drawers until they button up (absorb their yolk sac).


Outdoor runways

Once reaching juvenile stage, fish will be moved to outdoor runways where they will continue to grow

Once old enough, fish are moved to outdoor raceways where they continue to grow. Eventually they will be released where Californians can find them! If you want to see more and are in the area, Mokelumne River Hatchery is open for visits from 7-3pm for informal walking tours and are also available to do guided school tours if you call in advance.

Laura Goetz