Biofloc technology, commonly abbreviated as BFT, is essentially a recirculating system built around microbes rather than mechanical filtration. The tanks hold a dense, suspended community of microalgae, autotrophic and heterotrophic bacteria, fungi, ciliates, protozoans, and small zooplankton such as rotifers, copepods, and nematodes, all maintained with minimal or zero water exchange. The central trick is the manipulation of the carbon-to-nitrogen ratio. Fish excrete nitrogenous waste, chiefly ammonia, which is toxic at even modest concentrations. By adding an external carbon source such as molasses, sugar, glucose, wheat flour, or regional agricultural by-products, farmers push the ratio high enough that heterotrophic bacteria dominate. These bacteria assimilate inorganic nitrogen directly into their own cell biomass, converting a pollutant into living feed. The resulting aggregates, the flocs themselves, remain suspended in the water column and are grazed by the cultured animals.

The nutritional payoff is substantial. According to the review, biofloc typically contains 12 to 50 percent protein, 0.5 to 41 percent lipids, 14 to 59 percent carbohydrates, and 3 to 61 percent ash on a dry-weight basis, with the exact profile depending on the carbon source, salinity, and species cultured. Marine bioflocs are especially rich in essential amino acids including valine, lysine, leucine, phenylalanine, and threonine, although they can be deficient in vitamin C, arginine, methionine, and cysteine. Beyond macronutrients, flocs deliver bioactive compounds such as essential fatty acids, carotenoids, chlorophylls, free amino acids, and trace minerals, which support cell membrane integrity, antioxidant defenses, reproduction, and immune function. Researchers cited in the review note that biofloc is a valuable protein source not only for tilapia and prawns but also for mussels, and studies have shown that shrimp raised in biofloc systems accumulate more nitrogen in their biomass than those in conventional cultures.

The consequences for feed economics are significant, because feed is the single largest cost in most aquaculture operations. By recycling organic waste into in-situ microbial protein, BFT reduces dependence on expensive commercial feeds, and the review reports lower feed conversion ratios and higher protein efficiency ratios across numerous trials. In one experiment on Nile tilapia, daily addition of molasses as a fresh carbon source increased growth rates and productivity while cutting costs by 15 percent and raising profitability by 25 percent. Feeding strategy matters too: tilapia fed twice daily under biofloc conditions achieved 100 percent survivability and production of 11.27 kilograms per cubic meter, while reducing labor costs. Because the system also slashes water exchange, it conserves two of aquaculture’s scarcest resources, water and land, making high-density culture feasible for small-scale and resource-limited farmers.

Getting the carbon-to-nitrogen ratio right, however, is a delicate balancing act, and much of the recent literature reviewed by the authors focuses on finding species-specific optima. In stinging catfish, researchers tested ratios of 12, 15, 18, and 21 and found that a ratio of 15 produced the highest protein content and lowest moisture in the fish, with no significant differences in lipid and ash among the higher treatments. In common carp, sugarcane molasses raised the ratio and stimulated bioflocculation and heterotrophic bacterial growth, with a ratio of 19:1 improving water quality and growth, but pushing to 23:1 worsened feed conversion, protein efficiency, and feed intake. Ratios above 20:1 led to accumulation of dissolved salts and settled biomass that destabilized the system. In common carp fed at ratios of 10:1, 15:1, and 20:1, the highest ratio proved optimal for physiological and immune responses as well as growth, underscoring that the ideal value shifts with species, carbon source, and culture conditions.

Water quality dynamics explain why these thresholds matter. As carbon input rises, heterotrophic bacteria proliferate, and the resulting bacterial biomass, aggregated organic matter, and floc particles drive total suspended solids upward. Mineralization of that organic matter releases dissolved ions, raising total dissolved solids as well. Meanwhile, pH, total ammonia nitrogen, and nitrite nitrogen tend to fall as the ratio increases, because bacteria assimilate the nitrogen before it becomes toxic. In trials with Nile tilapia in cement ponds, both sugarcane molasses and wheat flour significantly lowered pH, unionized ammonia, and nitrite compared with controls, while nitrate and suspended solids climbed. Elevated nitrogenous compounds can inhibit nitrification and degrade water quality, so operators must monitor solids and be prepared to remove excess floc, often through settling basins or filtration.

One of the most striking findings synthesized in the review is the immune boost that biofloc microbes appear to provide. Specific microorganisms in the floc community function as natural probiotics, and fish and shellfish raised in these systems show significantly higher phagocytosis rates, nitroblue tetrazolium and myeloperoxidase activity, alternative complement pathway activity, total immunoglobulin levels, lysozyme activity, and antioxidant enzymes such as superoxide dismutase and catalase compared with animals in conventional systems. The practical result is greater resistance to major pathogens including Aeromonas hydrophila, Vibrio harveyi, Streptococcus agalactiae, and Edwardsiella tarda. Hematological studies reinforce the picture: genetically improved farmed tilapia in biofloc systems showed elevated serum glutathione peroxidase and lysozyme activity, common carp given cane molasses showed markedly reduced stress, and tilapia reared with zero water exchange displayed increased red blood cell counts and hemoglobin alongside reduced cortisol, liver enzymes, and urea, indicating improved welfare and homeostasis.

The microbial ecology underpinning these benefits is complex and still being mapped. Floc-forming microbes secrete extracellular polymeric substances that glue particles together and stabilize the aggregates, while nitrifying bacteria handle chemoautotrophic oxidation of ammonia, and grazers such as rotifers and protozoans recycle nutrients and enrich the floc as a food source. Systems are typically classified as green water biofloc, exposed to natural light and driven by both algal and bacterial processes, or brown water biofloc, run in closed environments where bacteria alone regulate water chemistry. Community composition shifts with the carbon source, salinity, and cultured species, and phytoplankton contribute by absorbing excess nutrients and producing dissolved oxygen. Managing this living suspension, rather than sterilizing it, is the fundamental philosophical shift that distinguishes biofloc from conventional intensive culture.

The technology is not without drawbacks, and the review is candid about them. Continuous, vigorous aeration is required to satisfy the biological oxygen demand of both animals and microbes, driving up energy consumption and operational costs. High water temperatures can favor pathogenic microbial growth, and accumulated organic load degrades water quality if solids management lapses. Consumer acceptance of fish raised in microbial floc also remains an open question that the authors say must be addressed ethically and transparently. Current applications concentrate on herbivorous, detritivorous, and bottom-dwelling species such as tilapia and shrimp; extending the approach to carnivorous fish will require redesigned carbon dosing and system architecture. The authors recommend optimizing biofloc concentrations, compartmentalizing system components for better control, and investing in farmer training and financial support to widen adoption.

Even with those caveats, the trajectory is clear. Biofloc technology aligns economic self-interest with environmental stewardship, turning the aquaculture industry’s most stubborn waste problem into a protein asset while cutting water use, land requirements, and antibiotic dependence. For policymakers and investors seeking responsible aquaculture growth, and for smallholder farmers in water-scarce regions who cannot afford conventional recirculating systems, the review positions biofloc as a practical bridge between rising global fish demand and the ecological limits of the planet, provided that research continues to refine carbon management, microbial community control, and species-specific system design.

Subject of Research: Biofloc technology for sustainable aquaculture: nutrition, water quality, and system efficiency

Article Title: The role of biofloc technology in sustainable aquaculture: nutritional insights and system efficiency

Article References: Yadav, N. K., Paul, S., Patel, A. B., Mahanand, S. S., Biswas, P., Choudhury, T. G., Baidya, S., & Meena, D. K. (2025). The role of biofloc technology in sustainable aquaculture: nutritional insights and system efficiency. Blue Biotechnology, 2(1), Article 7. https://doi.org/10.1186/s44315-025-00025-x

Image Credits: AI Generated

DOI: 10.1186/s44315-025-00025-x

Keywords: biofloc technology, aquaculture, sustainability, carbon-nitrogen ratio, water quality, fish nutrition, tilapia, shrimp farming, microbial protein, feed conversion ratio, fish immunity, wastewater recycling