Biofloc – Macroaggregates of algae, bacteria, protozoans, and other kinds of particulate organic matter such as feces and uneaten feed. Each floc is held together in a loose matrix of mucus that is secreted by bacteria, bound by filamentous microorganisms, or held by electrostatic attraction, i.e., an undefined composition (anything that will grow).
Shrimp farmers around the world are increasingly switching to a biofloc system for aquaculture. Biofloc systems were developed to improve environmental control over production. In places where water is scarce or land is expensive, more intensive forms of aquaculture must be practiced for cost-effective production. There are strong economic incentives for an aquaculture business to be more efficient with production inputs, especially the most costly (feed) and most limiting (water or land). High-density rearing of fish typically requires some waste treatment infrastructure. At its core, biofloc is a waste treatment system.
The microbial ecology of bioflocs is understood at only the most basic level. In particular, the role of biofloc in controlling or encouraging pathogenic bacteria, especially Vibrios, requires further investigation. Vibrios will accumulate in shrimp biofloc systems and can switch on and off their capacity to cause disease. This switching occurs in biofloc systems managed at low or high solids concentrations.
Potential pathogens are not limited to Vibrio, biofloc conditions are conducive to growth of other bacteria that may or may not constitute human pathogens. In a study published by Camila Brito et al. entitled “Microbiological quality of Litopenaeus vannamei culture using conventional and biofloc systems” it is stated “the end product (shrimp) is vulnerable to contamination at all stages of the process, including the rearing tanks, where current practices prioritize to raise stocking densities and the minimization of water renewal.
Addressing this concern, it is thus important to evaluate the potential of these systems for the proliferation of undesirable microorganisms, which may render the product unfit for human consumption. In the present study, the presence of coagulase-positive Staphylococcus, Salmonella spp., Vibrio spp., and total and thermotolerant coliforms was verified in biofloc tank and conventional pond systems used for the rearing of Litopenaeus vannamei in Pernambuco, Brazil, and the results were compared with the legislation regulating the marketing of fresh shrimp. Samples were collected from two biofloc tanks with a density of 375 shrimp m−2, and two conventional ponds with 12 shrimp m−2. None of the samples tested positive for either Salmonella spp. or coagulase-positive Staphylococcus, which is consistent with the legislation. While no standards are defined legally for Vibrio spp. or coliforms, very low concentrations were recorded in both systems, in comparison with other studies. While some variation in bacterial contamination was observed over the rearing process, the end product of both systems was fit for human consumption. The results of the study indicate that, while the water is not renewed in the biofloc system, the development of undesirable microorganisms can be controlled, with no adverse effects for the end product.