watersheds.org the world in your watershed search
homewhat's newabout ussite mapcontact us

Outdoors Fishing Spawning at Rockbridge Trout Ranch

  Spawning at Rockbridge Trout Ranch
  We visited Rockbridge last spring and saw young trout hatchlings growing in tanks. But we were too late to see the actual spawning happen.

Bud McCullough, Hatchery Manager, invited us to come back in late fall. That's when trout spawn in the wild. Once a week between late October and late December, they do the spawning at Rockbridge. One early December morning we went there to watch.
Bud McCullough has been working with the trout here for 27 years. He has observed his fish carefully over the years. He also visits other hatcheries to continue learning. He says the most important thing is to know your own water. For instance, different water temperatures make big differences in the best weights of spawning females at different hatcheries.
The outdoor tanks at Rockbridge are fed from Morris Spring, just down from Rockbridge Spring. To the right you can see an aerator adding extra oxygen to the water. Normally the spring produces enough water with enough oxygen for the thousands of fish in the tanks. But 2000 was the driest year since they began in 1944. They had to bring out the aerator to keep the fish healthy. Lots of fish penned in a small space need to "breathe" lots of oxygen, more than the reduced flow carried.
The spawning set-up includes an umbrella to keep the sun off harvested eggs from females and milt (the reproductive cells) from males. Otherwise, infrared rays in direct sunlight would kill these delicate cells.
They keep about 150 two-to six-pound males for breeding. Bud can "milk" (squeeze the milt out) all the males once a week throughout the season.
The first step is to fill a barrel with 10 gallons of water. The next is to add one teaspoon of an anesthetic drug to each 5 gallons of water. This drug puts the fish to sleep.
Meanwhile, Keith McKee scoots the males along toward Bud with a screen, to make them easier to catch.
Bud nets out two or three males and dumps them in the barrel. In a couple of minutes they'll be temporarily asleep and easier to handle.
Milking the males: They must keep the milt away from water. It lives only 15-30 seconds after touching water! This seems like a very short time. We could find out why by studying how trout spawn in the wild.
Bud squeezes along the male's belly, from its midsection toward the tail. Then he directs the milky milt into the cup Keith is holding. They will fill up four of these cups, one for each container of eggs. Keith will carefully cover the cups of milt and set them under the umbrella.
Bud throws the milked males back, where they sleep off the drug. They'll be swimming again in three to five minutes.
Milking the females: Rockbridge keeps 600 females for breeding. Each one can spawn once a year. Each female has two egg sacs, one along each side of the belly. On this day there are still about 200 females who have yet to spawn. Bud can tell from experience which ones are ready. He can feel when their bellies are full enough. Bud has chosen 40 females ready to spawn. They're penned in a center tank. Most are six pounds, a few over ten. Bud finds the smaller ones easier to handle.
Bud nets several females into the barrel, puts them to sleep, and then begins to milk their eggs. He squeezes from behind the head toward the tail.
Out comes a stream of eggs. Keith holds a strainer as Bud directs them into it. The eggs floated in a salty solution when they were inside the fish. Now they drain it off.
Fertilizing the eggs
It takes about ten females to fill this 16-cup container with 20,000 eggs. Today they will fill four of them. Over the entire season they fill about 100 such containers. That's a lot of eggs! Each egg could become a baby fish. Only about 52% of them actually do.
Now it's time to start growing baby fish! First step is to pour in saline (salt-water) solution. The salty water opens the micropyle (tiny opening) in each egg. It will also instantly activate the milt.
In goes the milt. Each of these millions of microscopic cells has 15-30 seconds to find and enter the micropyle of one of the eggs. Most won't make it.
Bud quickly mixes eggs and milt. The seconds are ticking away!
The fertilized eggs set for 15 minutes. Then they're poured into a bucket of water for an hour. This "hardening off" process changes the soft, jelly-like eggs. They turn into tough, elastic balls to protect the tiny fish embryos. These eggs will be their homes and source of food for the next 21 days.
Keith lowers the bucket to keep the eggs cool. From there they will go into containers in the basement hatchery. Notice that he uses his coat to shade it from the sun.
When they hatch, they'll go into the basement tanks.

Related Stories

Rockbridge Hatchery Tour

History of Rockbridge

Rockbridge Mill

  Text and photos by Peter Callaway.