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 other countries 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. 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 project focused on assessing the effect of stocking density in a RAS on production dynamics and stress response of olive flounder in nursery-level RAS.
In this study, fingerling (~58 gm ) olive flounder were stocked at three densities : 2.7, 5.8 and 8.1 kg/m2 (low-density: LD, medium- density: MD, and high-density: HD) in 1.2 m2 fiberglass tanks. Each of these three treatments was replicated in three randomly assigned tanks connected to a common sump and shared filtration system . To maintain clear water, 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 blood glucose, cortisol, growth hormone and Insulin like growth factor (IGF-1) concentrations were analyzed using a Dynex DS2 System (Chantilly, Virginia, USA), an automated ELISA (Enzyme-linked immunosorbent assay ) processor.
This research is currently ongoing; however, as of the most recent fish sampling event, fish were largest in the LD tanks followed by MD, and lastly the HD treatment . According to the assumed survival (very few mortalities have been detected), biomass is highest in the HD treatment, followed by MD, then LD. Upon harvesting fish from the experiment, d ata will be analyzed in detail comparing average weight, growth rate, total harvest, FCR, and condition factor between fish raised at the different stocking densities. Similarly, the collected blood samples will also be analyzed to compare stress hormone concentrations between the three treatment levels. Results of this study will be presented. At the end of this project we expect to better understand the tradeoffs of various stocking densities in olive flounder RAS. This trial will further develop inland production of marine species and provide growers with an alternative species for intensive, indoor production.