A comparison between water exchange and settling tank as a method for suspended solids management in intensive biofloc technology systems: effects on shrimp (Litopenaeus vannamei) performance, water quality and water use

Biofloc systems rely on microbial processes in the water column to recycle animal waste products, reducing the need for water exchange. These increases biofloc concentration in the water and some form of removal is needed. An experiment was carried out to evaluate two management practices to control biofloc in Litopenaeus vannamei culture. Six tanks (48 m(3)) were divided into two treatments: water exchange and solid settler. Shrimp were stocked at 164 shrimp m(-2) and with 0.67 g of weight. After 61 days, shrimp under solid settler treatment demonstrated mean weight of 12.7 +/- 0.5 g with survival of 73.8 +/- 1.4%, and those under water exchange had a final weight of 10.1 +/- 0.2 g and survival rate of 57.8 +/- 11.1%. Total suspended solids did not differ between the treatments: 326.8 +/- 24.9 mg L-1 for water exchange and 310.9 +/- 25.3 mg L-1 for solid settlers. Settleable solids and productivity/respiration ratio was higher (P < 0.05) in water exchange treatment, indicating differences in physical and biological characteristics of bioflocs. Solids removal method influenced the water use, in which 1150 +/- 249 L of water was necessary to produce one kilogram of shrimp using water exchange strategy, and 631 +/- 25 L kg(-1) with the use of settlers. Our results indicate that continuous operation of settlers can reduce variability in solids characteristics and water quality variables such as ammonia. Both strategies are efficient in controlling biofloc concentrations of the water; however, settlers can reduce water use and improve shrimp production.