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
"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,"
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