Texas Agricultural Experiment Station, Shrimp Mariculture Research Facility (TAES-SMRF) in Corpus Christi is developing a biosecure intensive nursery raceway system with limited discharge and the preliminary results are encouraging. A study was conducted to evaluate the effects of three methods to reduce particulate matter load in nursery tanks and the effect on growth, survival, feed utilization and selected water quality indicators. One raceway (#1) was equipped with a bead filter, the second raceway (#2) was equipped with a rapid sand filter, while the third raceway (#3) was provided with a foam fractionator.

On June 20, 2003, TAES-SMRF finished the harvest of the three 45 m³ raceways stocked 74 days earlier with five-day-old PL of the Pacific white shrimp Lito-penaeus vannamei. Each raceway was equipped with a center partition, six banks of 5.1 cm airlift pumps, six air diffusers, a rapid sand filter, a Venturi injector and sensors with dial out alarm system. To evaluate the effect of bead filter and foam fractionator, the rapid sand filter was not used on raceway #1 and #3.

The airlift pumps created water circulation enhanced by a high-pressure centrifugal pump that pumped water through a pipe with spray nozzles positioned under the partition. Raw seawater was treated with 10-ppm chlorine prior to stocking of the raceways.

Temperature, DO, pH and salinity were monitored at least twice daily. Settleable solids were recorded daily starting on day 49. Ammonia, nitrite, nitrate, reactive P, TSS, VSS, cBOD5 and COD were monitored weekly.

The best results were received in a raceway that was equipped with a rapid sand filter that was stocked at a density of about 6,500 PL/m³. Shrimp survival at harvest in this raceway was: 100%; average weight: 0.89 g; FCR: 1.09; biomass load: 5.25 kg/m³ and with less than 0.5% of new water added daily to offset evaporation and water losses to cleaning of the sand filter. Feed used was Rangen 45/10 and 40/5 (crumble # 0, 1, 2, 3 & 4). During the first week after stocking, the postlarvae were fed Zeigler PL Redi Reserve and newly hatched Artemia nauplii. It is important to mention that throughout the nursery study the shrimp showed no external fouling or signs of infection by chitenoclastic bacteria. The survival rates in the other two raceways were 96.3% and 97.8% for the bead filter and foam fractionator, respectively, although a lower stocking density was used in the raceway operated with the bead filter (3,800 PL/m³ vs. 5,000 PL/m³).

The result from raceways operated with the sand filter represents a world record for juvenile shrimp production under limited discharge. Although these are preliminary results, further research in this area certainly looks promising.