The olive flounder (Paralichthys olivaceus) sometimes referred to as Japanese flounder is a highly valued fish in East Asia due to its rapid growth, excellent aquaculture performance, and high market value. T his species has been domesticated in Korea starting in the 1980’s and has potential as a lucrative aquaculture candidate in U.S. as well. Recirculating aquaculture systems (RAS) reduce the amount of water and space required to intensively produce seafood products . In landlocked states such as Kentucky, where shrimp production in RAS systems has been growing, olive flounder can be reared in the same flat-bottom culture tanks used for shrimp. Although clear water RAS has a somewhat high up-front cost, it can be an effective strategy for intensive rearing of olive flounder at nursery stage as it not only ensures higher productivity but also maintains optimum water quality of the culture system. Rearing fingerlings in separate nursery tanks at high density ensures better utilization of space and animal inventory. Stocking density is one of the major factors affecting animal welfare and system productivity . The level of stress resulting from high stocking density may also affect energy and metabolism, potentially affecting growth rates and suppressing the immune response. This research focuses on assessing the effect of stocking density on production and health of olive flounder at nursery level in RAS.
In this study, fingerling (20-30 gm) olive flounder were stocked at three different densities : 1.2, 2.4 and 3.6 kg/m3 in 1.2 cubic meter fiberglass tanks. Each of these three treatments were replicated in three randomly assigned tanks connected to a common sump and shared filtration systems . To maintain a clear water RAS, water from the tanks passed through a drum filter with 40 µm screen , foam fractionator, and a moving bed bioreactor (MBBR) aerobic bio filter. Ozone (O3 ) gas was injected into the fractionator reaction chamber and water then passed through a UV radiation lamp to destroy ozone and further sterilize the water . In order to prevent the accumulation of nitrate, an anaerobic MBBR denitrification chamber was also used. To assess the health of olive flounder, stress indicators including glucose level, plasma cortisol level, growth hormone and Insulin like growth factor (IGF-1) were also analyzed using a Dynex DS2 System (Chantilly, Virginia, USA) an automated ELISA (Enzyme-linked immunosorbent assay ) processor.
Results from this experiment are pending but expected to show significant differences in the average weight, growth rate, total harvest, FCR, and condition factor between fish raised in the different stocking densities. We expect that fish may grow slower as density increases, but that the number and biomass of fish produced at high density will likely offset this reduction. It is also expected that the level of stress hormones will be significantly different among the three-treatment levels, increasing with augmented density, especially towards the end of the experiment. Overall, at the end of the research project we are expect ing to better understand the tradeoffs that come with density level so we can make recommendations to farmers.