Spawning steelhead and egg Care

Bill Nyara

Manager

South Santiam Fish Hatchery

For the crew at South Santiam Hatchery, winter means summer steelhead spawning and egg care. Along with the normal, routine tasks (fish feeding, pond cleaning, maintenance, etc.), the crew conducts spawning operations on one day, every other week.

From late December through early February, 500 female and 500 male steelhead are spawned at the hatchery. These are the fish that were collected all summer long at the trap at Foster Dam. They’ve been held in the holding pond at the hatchery until they matured or ripened.

The water level in the pond is lowered so that the fish can be crowded to one end, netted, and anesthetized in a large tub. The females are checked for ripeness by gently squeezing their bellies. If the female is ripe, the eggs are loose and a few will squirt out when squeezed. These ripe females are placed in live boxes at about 75 fish per box. Once all of the females in the pond have been sorted like this, the actual spawning operation begins.

The ripe females are removed from the live box, quickly killed, and placed in a rack. The tail of each female is cut to bleed the fish and reduce the amount of blood in the eggs. The eggs (about 3,500 in each fish) fall into a bucket as the belly of the fish in cut open. Males are gathered from the opposite side of the pond during this process. Milt from each male is collected in a separate cup. The eggs from each female are then fertilized with this cup of milt. This results in a one to one spawning ratio and provides good genetic variability in the offspring.

Ovarian fluid from each female and milt samples from each male are taken to OSU for virus screening. Each bucket of eggs is tracked by sample number. In about a week, results from these samples determine if either parent carried the virus. Each bucket of fertilized eggs is poured into an incubator tray. The trays are also labeled to coincide with the virus sampling. Eggs from positive parents can’t be utilized as freely as negative eggs. Often times, positive eggs are destroyed as surplus to program needs. There are always more eggs taken each season than is necessary in anticipation of some being from virus-positive parents.

A constant flow of fresh water travels through the stack of trays. The eggs stay in these incubator stacks, undisturbed, as the embryos slowly develop. The speed of development is directly related to the temperature of the incubation water. The safe range for incubation water temperature is 33 to about 60 degrees. The warmer the water, the faster the eggs develop. The typical temperature range of the hatchery’s water is 40- 45 degrees during the winter. Since the development of the eggs is temperature dependant, eggs from a later spawning can be “accelerated” by incubating them in warmer water. This is possible with the use of well water. By using 56 degree well water, eggs that are fertilized two weeks from now can easily catch up to the same stage of development as those fertilized today.

Once the eggs develop to the “eyed stage”, they can be handled. This is when the embryos have developed to the point that their large, black eyes are clearly visible in each egg. This is when the work really begins. The hatchery incubates almost two million summer steelhead eggs annually.

Next week, I’ll explain how the hatchery picks, counts and ships the eggs to other fish hatcheries.

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