Two trials were conducted to determine the effects of growing Pacific Whiteleg Shrimp (Litopenaeus vannamei ) with high raceway stocking (equivalent to more than 7kg/m^2 at 39g maturity ) in typical low-salinity water . In the first trial, bubble aeration was used until the oxygen demand could not be met, and then a partial shrimp harvest was completed each time the biomass loading reached about 4kg/m^2. In the second trial, an oxygen infusion process was used to provide raceway dissolved oxygen concentrations at 150% of atmospheric saturation , allowing essentially all the animals to reach maturity.
The two three-month trials (90-day nominal maturation) were conducted in a greenhouse-enclosed concrete raceway with a bottom area of 97.9m2 and an average water depth of 57cm . The water was held at about 30°C, with a salinity of 13ppt. A recirculation system (RAS) was used to biologically control NH3 and NO2- and partial water exchanges were completed as required to control NO3- . The initial stocking was approximately 21,000 post-larvae shrimp in each case, with an estimated 25% loss on planting for an expected 15750 live animals . For the second trial, d issolved oxygen was maintained at 50% above atmospheric saturation by the Fuel Tech, Dissolved Gas Infusion (DGI) technology across all growth phases.
In the DGI trial, excellent survival and growth was achieved and a mean weight of 42g was reached in about 100 days with a survivability of about 50% . In fact, the individual shrimp growth curves show no significant change from the trial in which selective harvesting was required . High PL stocking and reliable DO dosing with automatic controls dramatically increased total production as compared to the first trial.
Other observations from the trial include no evidence of trimethyl amine odor at harvest, no evidence of oxidation, no evidence of excessively fast metabolism, no evidence of osmotic shock and no evidence of gas bubble disease, suggesting that in low-salinity water maintaining dissolved oxygen levels above saturation without the presence of bubbles increases the yield while minimizing detrimental effects of high oxygen levels.