HETEROTROPHIC VS. MIXED BIOFLOC SYSTEMS: IMPACTS ON USE OF WATER, SUSPENDED SOLIDS PRODUCTION AND ZOOTECHNICAL PERFORMANCE OF Litopenaeus vannamei

Hellyjúnyor Brandão, Dariano Krummenauer, Íris Xavier, Gabriel Santana, Henrique Santana, and Wilson Wasielesky* 
 
Universidade Federal do Rio Grande - Instituto de Oceanografia, Rio Grande, RS, Brasil. E-mail: manow@mikrus.com.br
 

The Biofloc Technology System (BFT) is characterized by the use of bacteria to remove nitrogenous compounds from the water, guaranteeing better water quality and little or no water renewal. Two major groups of bacteria are involved in the removal of nitrogen in this system: heterotrophic bacteria, through the incorporation of inorganic Nitrogen and organic Carbon into their biomass, and autotrophic bacteria, which perform nitrification through the oxidation of ammonia to nitrite and then nitrate. In this way, different techniques can be used for the formation and maintenance of the bioflocs, depending on which group of bacteria is wanted to be the dominant. The objective of this study was to analyze the effect of bioflocs formation techniques and their effects on the zootechnical performance of L. vannamei, on the use of water and on the production of suspended solids.

A 60-day trial was conducted at the FURG's Marine Aquaculture Station. Shrimp juveniles (7.05 g ± 1.37) were stored in 150 liter tanks at storage density of 300 / m³. Four treatments (n = 3) were tested using different floc formation techniques: no supplemental organic fertilization, fertilization according to the nominal ammonia reading (mixed heterotrophic/chemoautotrophic) and daily fertilization according to the estimated ammonia produced (heterotrophic). The temperature, salinity, dissolved Oxygen, pH, ammonia, nitrite, nitrate, alkalinity and total suspended solids (TSS) of the water were monitored. Water renewal was done every time ammonia, nitrite and SST levels exceed predetermined limits. The results were analyzed by ANOVA one-way and Tukey's test (α = 0.05).

The water quality parameters were influenced by the treatments (P <0.05), with differences in the concentrations of ammonia, nitrite, nitrate, pH, alkalinity and SST. The heterotrophic treatment had the lowest nitrate value, due to the predominance of heterotrophic bacteria, as well as higher pH and alkalinity levels, since these bacteria do not use inorganic carbon. There were significant differences in the zootechnical parameters, being the highest final weight and productivity, as well lower FCR, found in the mixed treatment. There were no significant differences in survival. The total volume of water used presented lower values ​​in the mixed treatment, while solids removed was almost four times higher in heterotrophic treatment compared to the others. These results showed the importance of adopting a mixed heterotrophic/chemoautotrophic biofloc system to optimize water use and decrease solids production.

Acknowledgments: CNPq, CAPES, FAPERGS, Guabi, Trevisan, INVE, Aquatec e All-Aqua.