An evaluation of management crteria for biofloc systems used in high-density early life stage rearing of marine penaeid shrimp at low and high salinity

Biofloc technology is a proven, environmentally-sustainable method that reduces potentially-harmful discharge, capital costs for facility construction, and expensive feed inputs. Therefore, the use of biofloc technology, normally applied to grow-out production, was applied and evaluated for shrimp Litopenaeus vannamei nursery systems. The objective of the study was to evaluate nitrogen management in a shrimp nursery biofloc system at 1) low and high salinity (8 and 28 ppt), and 2) low and high biomass density (~20 g/m2 and 300 g/m2). Three 14-15 day nursery trials were conducted with postlarval or juvenile shrimp. Mean TAN levels were 0.63±1.17 and 0.85±1.17 mg L-1 in Trial 2 and 0.18±0.29 and 0.17±0.29 mg L-1 in Trial 3 for the 8 and 28 ppt treatments, respectively. There was no difference in TAN concentration between treatments in either trial (p = 0.46 and 0.77 Trial 2 and 3, respectively). Mean NO2 levels were 3.00±1.63 and 4.68±2.54 mg L-1 in Trial 2 and 1.64±0.17 and 2.72±0.23 mg L-1 in Trial 3 for the 8 and 28 ppt treatments, respectively. Nitrite was significantly higher (both p < 0.01) in the 28 ppt treatment of both Trials 2 and 3. Results suggest that nitrogen can be controlled at either salinity and at either low or high biomass density. In addition, the system described in this study showed good potential for stocking substantially higher densities (up to 0.49g/L vs 0.03 g/L currently stocked) of postlarvae. Biofloc-managed systems will be key in increasing the carrying capacity of nursery systems, but certain management issues (e.g., stocking procedure, establishing and maintaining ideal biofloc level and cost:benefit ratio) still remain to be investigated.