Biofloc vs Mixotrophic System
By Dr. Wiphada Mitbumrung, Ph.D. Applied Marine Biosciences — Mon Jul 27 2026
Biofloc and mixotrophic systems are both pond management approaches designed to improve water quality, recycle nutrients, and reduce waste accumulation. However, they are not the same system. The main difference is the biological pathway used to control nitrogen and organic matter in the pond.
In a biofloc system, the pond is managed mainly to promote heterotrophic bacteria. These bacteria use organic carbon and nitrogen waste, especially ammonia, to build bacterial biomass. To support this process, farmers often add an external carbon source such as molasses or other carbohydrates. The goal is to increase the carbon-to-nitrogen ratio so heterotrophic bacteria can rapidly assimilate ammonia into microbial floc. These flocs can later become a supplemental natural food source for shrimp.
Biofloc can reduce ammonia quickly when the system is well managed, but it also creates a high bacterial load and high suspended solids. Because heterotrophic bacteria grow fast and consume a large amount of oxygen, biofloc ponds require strong aeration, good mixing, and regular monitoring of total suspended solids. If the floc becomes too dense, it can stress shrimp, clog gills, reduce water quality, and increase the risk of oxygen depletion, especially at night or during cloudy weather.
A mixotrophic system does not rely on heterotrophic bacteria alone. Instead, it uses different biological groups according to the stage of culture. The main idea is to shift the pond ecology step by step, based on shrimp size, feed input, organic waste level, and pond carrying capacity.
In the first phase, the system relies mainly on phytoplankton. This stage is important after stocking because post-larvae and small shrimp benefit from natural productivity in the pond. Phytoplankton provides natural food, supports the pond food web, helps stabilize water color, and gives natural shade to small shrimp. This shade reduces stress and helps create a more suitable environment during the early culture stage.
In the second phase, heterotrophic bacteria are introduced more actively because organic waste starts to increase. As shrimp grow and feeding rate increases, uneaten feed, feces, dead plankton, and dissolved organic matter begin to accumulate. Heterotrophic bacteria help decompose this organic matter and reduce the build-up of waste before it becomes sludge or creates toxic metabolites.
In the third phase, the system relies more strongly on heterotrophic bacteria because shrimp depend mainly on commercial feed. At this stage, feed input is high, and organic waste from uneaten feed and feces becomes the main pressure in the pond. Heterotrophic bacteria play a major role in breaking down organic waste, reducing sludge formation, and helping maintain water quality. At the same time, nitrifying bacteria should also be supported to convert ammonia and nitrite, so the nitrogen cycle remains stable.
Therefore, mixotrophic management is a staged and balanced approach. It begins with phytoplankton dominance for natural productivity and shade, then gradually increases bacterial support as organic waste increases, and finally focuses on strong waste decomposition and nitrification during the high-feeding stage. Compared with biofloc, mixotrophic management does not aim to create excessive suspended floc. It aims to maintain a stable pond ecosystem where phytoplankton, heterotrophic bacteria, and nitrifying bacteria work together according to the needs of each culture phase.
In simple terms, biofloc depends mainly on fast bacterial assimilation of waste, while mixotrophic management adjusts the biological system over time. It starts with phytoplankton, then introduces heterotrophic bacteria, and later strengthens bacterial waste decomposition and nitrification. For shrimp farming, the best system is not only the one that removes ammonia quickly, but the one that keeps water quality, oxygen, pH, plankton, and microbial communities stable throughout the crop cycle.