WILMINGTON, NC -- Groundbreaking research by a University of North Carolina, Wilmington (UNCW) scientist may help keep flounder on your dinner menu.
Flounder, a popular flatfish whose numbers are declining in our oceans, was one of the top ten fish consumed in the U.S. according to a National Fisheries Institute survey in 1997. With world populations increasing from a present six billion, to nine billion in 2035, aquaculture or fish farming is the only recourse to meet consumer demands for this succulent fish.
This year, for the first time, the eggs of southern flounder were spawned naturally in a controlled environment without hormone induction in quantities that would be sufficient for a commercial operation. Aquaculturist, Wade O. Watanabe, at the Center for Marine Science Research at the University of North Carolina at Wilmington (UNCW), said this is another important step in being able to produce flounder for large-scale fish farming.
"Our operation shows that you can take wild adult broodstock out of the ocean, and provide the conditions necessary for them to spawn naturally that same year," Dr. Watanabe said. "In the past, for spawning to occur, fish were injected with hormones on a daily basis or implanted with hormone pellets. Now, through natural spawning of recently captured adults, we can minimize the acclimation period for wild-caught fish and the handling-stress on broodfish that would be required if hormones were used to induce spawning."
Funded by the U.S. Department of Agriculture, the National Oceanic and Atmospheric Administration, and North Carolina Sea Grant, Dr. Watanabe set up a brood tank system at the UNCW aquaculture facility in Wrightsville Beach, just east of Wilmington. Two black cone-shaped tanks, eight feet in diameter by four feet deep, have a volume capacity of 1,250 gallons.
Dr. Harry Daniels, a larval culture specialist at North Carolina State University, supplied wild adult southern flounder, obtained through commercial sources, for the project. Dr. John Burke of the National Marine Fisheries Service in Beaufort also donated broodstock for the project.
"Larval culture is Harry's expertise," Dr. Watanabe said. "Unlike freshwater fish (catfish, trout, tilapia), culturing larvae of a marine finfish like flounder is technically demanding. Freshwater fish produce large eggs with a lot of yolk. By the time the yolk is eaten, freshwater fish are developed enough to be fed a commercial fish chow. That's why freshwater aquaculture is well established, whereas, marine aquaculture is still in the embryonic stages. Marine finfish produce small eggs with small yolks. When their yolk is used up, they must be fed microscopic algae and zooplankton. The upshot is that the requirement for these tiny organisms is a difficult task to meet."
Since scientists believe southern flounder spawn during the winter in December and January, environmental conditions in the brood tanks were manipulated to simulate winter conditions for four and a half months from December through mid-April, 1998. During this period, a group of 24 flounder, weighing from 1-4 pounds and measuring from 14-20 inches long, produced an average of 50,000 fertile eggs per day, enough to satisfy the demands of an aquafarm business.
According to Dr. Watanabe, previous research has achieved natural spawning in a small laboratory scale, but never before in sufficient quantities for a commercial operation.
"While this is a major step," Dr. Watanabe said, "we're still a long way from being able to produce in all seasons of the year the quality of fingerlings that would be needed for a commercial industry."
With this milestone accomplished, Dr. Watanabe and Dr. Daniels are modifying the nutrition of broodstock and such environmental parameters as temperature and light to improve fertilization and survival of southern flounder eggs to the first-feeding larval stage.
An aquaculture venture that has already demonstrated success revolves around the southern flounder's cousin, the summer flounder, another subject of Dr. Watanabe's research. Summer flounder have a distinct pattern of five spots on the lower halves of their flat bodies, whereas southern flounder are more mottled in appearance. Both adult species lie on their side instead of their abdomen, and always look up. They are capable of changing color patterns to match the bottom color, ranging from blackish-brown to light gray. The down side of their body is white.
Dr. Watanabe pointed out that while there is at least one summer flounder hatchery, Great Bay Aquafarms in New Hampshire, the industry is constrained by a lack of published information on the growout stage from fingerling to marketable size, about two pounds.
More research is necessary to understand how to maintain broodstock in a healthy state, alleviate stress and avoid disease. How does a scientist know a fish is under stress?
"Experience helps," Dr. Watanabe said. "You observe appearance, growth rates and feeding habits. Gardeners who have success with plants are said to have green thumbs. In aquaculture, certain 'blue thumb' aspects are involved."
"One person can't do everything by himself in a field as broad as aquaculture. It requires a multidisciplinary approach," Dr. Watanabe said. "I place a high priority on doing collaborative research with scientists who've mastered different areas of expertise."
Dr. Watanabe is collaborating with Dr. Thomas Losordo, a NCSU engineer, and Dr. Christopher Dumas, an UNCW economist, on a growout study that could give the summer flounder industry the information it needs to be a financial success. This aspect of the project is funded by a grant from the W.R. Kenan Jr. Fund in Chapel Hill.
"Investors are reluctant to back commercial projects without sufficient data," Dr. Watanabe said. "We want to generate nonbiased scientific data. That's why we're here!"
UNCW's Chancellor James R. Leutze believes Dr. Watanabe's research has the potential to change the whole face of aquaculture in the Southeast.
"The flounder is a fish that's in trouble," Dr. Leutze said. "I'm remarkably impressed by the creative aspects of Dr. Watanabe's work and its practical benefits to the field of marine science. This research could have a wider impact than any other study in aquaculture."
"With world population increasing and ocean finfish decreasing," Dr. Watanabe said, "fish farming is our only recourse to provide desirable species such as the summer and southern flounder in sufficient quantities to meet the needs of consumers."
Materials provided by University Of North Carolina, Wilmington. Note: Content may be edited for style and length.
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