In the past, for spawning to occur, fish were injected with hormones on a daily basis or implanted with hormone pellets. 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.
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.