Jan 29, 2015

Ever wonder where stock Rainbow Trout come from? Look northeast of Lovell

LOVELL — Mother Nature is getting a helping hand, to the delight of Wyoming anglers.

Wyoming Game and Fish Department employees at Tillett Springs Rearing Station northeast of Lovell have been busy rearing and spawning fish.

On Dec. 17, those employees induced fertile Firehole River rainbow trout to lay approximately 340,000 eggs. Most will become fish.

By lightly squeezing the length of the female rainbow’s body, eggs are squirted out. The same technique is used to collect male milt to fertilize the eggs. Photo by Gib Mathers
About 5 percent of the eggs laid by rainbow trout in the wild survive to become live fish, said Brad Welch, hatchery supervisor at Tillett. Nature’s spawning beds are fraught with danger. Eggs in gravel beds can be crushed by that gravel, while insect larvae, raccoons, birds and other fish eat the eggs, Welch said.

Tillett, howeever, maintains a survival rate of more than 65 percent from egg to fish, Welch said.

The roughly 16-inch rainbows are kept in holding tanks before and after being relieved of their eggs or milt. Photo by Gib Mathers

At Tillett’s spawning building, employees took squirming females and males measuring about 16 inches from holding pens to collect their eggs and sperm.

“We will be crossing 4-year-old females with 3-year-old males and 3-year-old females with 4-year-old males,” Welch said in an email prior to the spawning operation. “The different age crosses are done to reduce the probability of crossing a sister with a brother or a father with a daughter. The concept is to maintain genetic integrity within the population.”

The fish were pre-sorted and held in separate pens or holding tanks.

Prior to spawning, employees sorted and checked the fish daily to make certain they were ready to lay eggs. The 4-year-old females had at least one of their pelvic fins clipped off to distinguish age difference. The three-year-old fish did not have any fins clipped, Welch said.

Concrete holding tanks separate the rainbows by age and sex to maintain genetic integrity while fertilizing the eggs. Photo by Gib Mathers

The spawning process closely resembled an assembly line. Spawning tables were set up to progress from the left to the right.

The far left table held anesthetic baths for the fish. The anesthetic — clove oil — is used to calm the rainbows and so make egg/sperm extraction easier, Welch said.

From left, Guy Campbell, hatchery assistant supervisor of development from Casper, and Chester Bettger, fish culturist from the Clarks Fork hatchery, watch Gregory Lehr, fish culture specialist at Tillett, ease a batch of Firehole River rainbow trout into the anesthetic bath to calm them. Photo by Gib Mathers

The rainbows’ next stop was the anesthetic rinse tub, followed by the spawning pans. The rinse is distilled water used to remove the anesthetic, said Gregory Lehr, fish culture specialist at Tillett. The employees “stripped” the eggs into the pans — large plastic bowls — and placed the fish into one of the recovery tubs at the head of the table. Then, no worse for wear, the trout were transferred back to the holding pens.
The female’s eggs are about the size of a pea. Photo by Gib Mathers

The eggs resembled tiny, shiny orange beads. Following an anesthetic and rinse, the males’ milt, or sperm, was added to the eggs in a pan. To extract eggs and milt, the employees gently squeezed the fish’s body downward, causing the gametes to jet from a fish rear like a squirt gun.

After the eggs were fertilized, a small amount of fresh water was added, and the bowl was gently swirled. A dash of water speeds sperm movement, Welch said. After the sperm is added, the eggs are rinsed again to remove any excrement and thus keep bacteria out, Welch said.

Pat Long, senior fish culturist at Tillett, thoroughly rinses the eggs to remove ovarian fluid, milt and any ordure to prevent the onset of bacteria. Photo by Gib Mathers

The approximate 340,000 eggs were sent to the Story hatchery to be incubated until they reach the eyed egg stage. Estimating a 35 percent loss from eggs to live fish, Clarks Fork hatchery will receive 133,000 eyed eggs from Story. Clark will then send back 88,000 to Tillett as 2 1/2-inch fish that Tillet will raise and stock as 7- to 9-inch fish. Clark will keep and raise the remaining 45,000 and stock as 7- to 9-inch fish.

Speas hatchery, near Casper, will get 153,000 eyed eggs from Story and plans to stock 130,000 4- to 5-inch fish.

There are 10 Game and Fish hatcheries in the state working in concert to raise a variety of fish species for anglers.

“And that’s how we get fish stocked all over the state,” Welch said.


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