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Released July 28, 2005

GCRL HITS MILESTONE IN SPECKLED TROUT PRODUCTION

Ocean Springs– When Gulf Coast Research Laboratory researchers brag about their catch of speckled trout, the numbers are in the thousands and the size under two inches.

The fish, known more formally as spotted seatrout and Cynoscion nebulosus, are also the first speckled trout ever raised on a production scale in an indoor aquaculture system. At 36 days old and about 1.5 inches, the fingerlings hit a milestone for the GCRL with their move from nursery to grow-out facilities.

Personnel at The University of Southern Mississippi lab moved the fish from round 264-gallon tanks in the nursery facility to roomier 12 x 50-foot raceways in a greenhouse at the GCRL on Tuesday, July 26.

The tiny speckled trout are part of a joint effort that the Mississippi Department of Marine Resources (DMR) and the GCRL launched in May 2004. Christened the Seatrout Population Enhancement Cooperative (SPEC), the project’s purpose is to develop the how-to for rearing Mississippi spotted seatrout in captivity and to test the use of hatchery-produced fish for enhancing the natural population of the popular species.

Researchers are using the fish to test how GCRL's intensive aquaculture system -- raising marine species in tanks at high densities -- will work with speckled trout.

Taking advantage of the success GCRL has had in developing marine aquaculture techniques, the project is applying these methods in raising marine shrimp and red snapper.

Results are on target. Lab personnel hatched the current crop of seatrout young from eggs they secured from Texas Parks and Wildlife aquaculture operations. The GCRL team reared the fish through day 25 with 18,500 surviving, better than a 24-percent survival rate.

"That is good for a first try," said Reginald Blaylock, Ph.D., principal investigator of the project.

"If we were talking about cows, 24 percent survival would be a disaster," added Jeffrey M. Lotz, Ph.D., also an investigator on the project. "In the marine aquaculture industry, 25 to 30 percent survival is pretty standard."

Depending on the size of the fish, a speckled trout will produce 100,000 to 750,000 eggs at a time. "Typically, marine fish produce a lot of very small eggs with low survival," he said.

At day 25, researchers moved the fish into tanks at three different population densities. The count that accompanied the Tuesday, July 26, exercise will provide a snapshot of the effects of crowding on growth and survival of the species in captivity, another important piece of the puzzle in intensive indoor fish farming.

Lotz said the most difficult part of early larval rearing is to get the newly hatched fish to feed.

"This was a dry run to see that our facilities are, in fact, working right," Lotz said. "We are confident now that we can run our own larval fish in the system. We are still continuing to test the juvenile rearing systems."

Blaylock said there is currently no ready supply for larvae from Mississippi seatrout, a challenge the team is working on as well. None of the Texas speckled trout will be released.

The project still faces a number of other challenges.

"The stage we are at now is to prevent cannibalism," Lotz said. "Spotted seatrout are aggressive predators. That is why they are such good game fish."

Tagging protocols are another line of experimentation. Researchers will periodically remove about 100 of the fish at a time to measure, weigh and tag them. The tagged fish will be held separately so researchers can track their growth and survival.

Angelos Apeitos, manager of the aquaculture component of the program, said the team will implant wire tags coded with letters and numbers to allow tracking of each fish's lineage, batch and size at tagging.

"We want to find out the earliest stage at which we can tag the fish without affecting their survival," Apeitos said. "We also want to be sure that they don't shed the tags as they grow."

Once Mississippi spotted seatrout are produced, tagged and released, the information on the tags from recaptured fish will help assess how well the pilot stocking program is working.

"If the results show that the released fish have a positive effect on Mississippi seatrout populations, then the use of cultured seatrout becomes a tool for supporting the fishery," Blaylock said. "It is another tool that goes into the tool box to maintain fisheries so they are not depleted."

The GCRL is part of the College of Science and Technology.

 

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July 28, 2005 11:22 AM