Raising rockfish: Trials in a NOAA lab

Endangered fish is too tasty for its own good
By Sara Bruestle | Apr 03, 2013
Courtesy of: Mark Tagal This "homemade" Brown rockfish was raised by scientists at the National Oceanic Atmospheric Administration lab in Mukilteo.

Any day now, two pregnant Copper rockfish are expected to give birth at the National Oceanic and Atmospheric Administration lab in Mukilteo.

NOAA scientists at the Mukilteo Field Station wait like expectant fathers for the time the females will release anywhere between 16,000 and 640,000 live young each.

It’s not easy raising rockfish, as there is no exact science to it – yet. There isn’t a lot of funding for it either. As such, Mukilteo’s is the only one of Northwest Fisheries Science Center’s five labs raising rockfish right now.

“If you wanted to raise salmon, there are salmon manuals, but they don’t really have that manual for rockfish,” said Mark Tagal, who raises fish for NOAA. “We’re [still] unlocking the secrets of growing them.”

Scientists at the Mukilteo lab raise rockfish and other marine fish to research their lifecycles and how toxins and pollutants affect them. The fish also serve as a good teaching tool for school children and other visitors.

“The rockfish that are here are good education and outreach tools,” said Dan Tonnes, the rockfish recovery coordinator. “Unless you’re a scuba diver, you can’t really see rockfish in the wild.”

The scientists’ overall goal is recovery. Three species of rockfish are so close to extinction that they are protected under the Endangered Species Act: Yelloweye, Canary and Boccacio. The first two are listed as “threatened,” the third as “endangered.”

There are about 30 species of rockfish in the Puget Sound, and 102 species worldwide.

The two pregnant females are on special loan from the Seattle Aquarium – the aquarium doesn’t loan its fish out to anyone else. Their young, or larvae, will be part of a display that shows the developmental stages of a rockfish.

“The main focus is the three [listed under the ESA], but we’ll take any rockfish they have because their lifecycle is pretty similar,” Tagal said. “It’s good practice.”

The reason rockfish are in danger of extinction is the same reason they’re so difficult to raise: They reproduce more like people than fish. Rockfish can live 100 years and take 17 years or more to reach reproductive maturity.

Rockfish were overfished for decades because they are both delicious and easy to catch. No one realized until about 30 years ago that the fish replace themselves at a snail’s pace.

“There are estimates of 70 percent decline for rockfish in the Puget Sound over the last 50 or 60 years,” Tonnes said. “It’s probably more than that.”

The process of raising rockfish has been one of trial and error over the last 15 years.

The larvae start out at 3-4 millimeters long, or about the length of an eyelash. Coppers have been found as large as 24.6 inches in the wild.

Scientists have essentially had to recreate the food web inside the lab to provide the larval fish with food microscopic enough to eat until they can stomach what many would call “fish food.”

Then there was the issue of the water tank. It took them about six years, but the scientists finally figured out that they needed to paint the walls of the tanks black and leave the bottoms clear so that the fish wouldn’t kill themselves by repeatedly swimming into the sides. There are no walls in the ocean.

“There’s actually a name for it – it’s called ‘head-banging mortality,’” Tagal said.

The scientists are still looking into other factors, including water temperature, flow and quality.

The Mukilteo lab borrows 3-15 pregnant females a year for research. A lot of their young go to NOAA divisions or other groups for experiments and other projects.

After about 30-50 days, most of the fish are sent off to projects in California, Oregon or as far away as Spain. By then, the tails, fins and spines of the larvae are starting to develop, and they are looking more like rockfish.

The number of larval fish scientists have at Day 50, however, is only a fraction of what they will start with.

The die-off rate is remarkable: Even with no predators and ample food, nearly 99 percent of the 640,000 young will die in the lab. It’s closer to a .0005 percent survival rate in the wild.

“The research end of raising them informs whether or not in the future that would be warranted or practical,” Tonnes said. “There are folks who may be interested in raising them for commercial purposes on the West Coast, and so that’s informative to them, too.

“They’ll need to consider how much effort it takes to raise a rockfish.”

Many of the rockfish raised in Mukilteo that don’t go to projects grow up and are either donated to the Seattle Aquarium or kept at the lab as pets. Tagal affectionately refers to them as “homemade” rockfish.

“They’re a real interesting fish to look at,” he said. “Salmon, they’re zipping around, but rockfish, they just kind of sit there and move real slow."

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