A COMPARISON OF BIOFLOC, CLEAR-WATER, AND HYBRID CULTURE SYSTEMS FOR INTENSIVE SHRIMP (Litopenaeus vannamei) NURSERY PRODUCTION  

Indoor, intensive recirculating aquaculture systems (RAS) are increasing in popularity for marine shrimp production as a way of providing fresh, high-quality, never-frozen shrimp to metropolitan markets year around.  One common stage in shrimp production is a nursery phase, which can enhance biosecurity, allow better quantification of animals, and utilize space more efficiently.  Nurseries are usually started a few days after shrimp develop to post-larvae (PL) and continue to a juvenile stage between about 0.5 and 1.0 g.  However, it is unclear what type of RAS is most appropriate for indoor shrimp nurseries.  

An experiment compared three system types, dictated by differences in filtration: clear-water RAS (CW), biofloc systems (BF), and hybrid systems (HY).  Each treatment included four, randomly assigned 208 liter culture tanks; CW systems had an external settling chamber, a foam fractionator, and a biofilter, BF systems included only a settling chamber, and HY systems included an external settling chamber, and a biofilter.  The nursery tanks were stocked with 3,000 PL/m³ with an initial weight of 7 mg, and shrimp were grown for 45 days.  Water quality parameters, including inorganic nitrogen concentrations (TAN, NO₂-N, NO₃-N), were measured once a week.  At approximately the middle of the study, samples of shrimp were weighed to determine mean individual weights.  An -value of 0.05 was used during data analysis to determine significant differences between treatments.  

Final data are still pending, but at about the halfway time point there were no significant differences in ammonia and nitrite concentrations between the treatments.  However, nitrate concentration was significantly greater in the HY tanks than in tanks from the other treatments (Table 1).  Mean individual shrimp weight was significantly greater in the BF treatment, followed by HY, then CW.  These results indicate that differences in system design can have significant impacts on water quality and nursery shrimp production, suggesting that producers should carefully consider what type of system may best suit their production goals.