In BFT, intensive heterotrophic growth in the culture water results in turbidity and may induce variations in DO levels due to increased microbial metabolism resulting from carbon dosing. Such varying DO levels may have a negative influence on the aquaculture organisms. The implementation of external heterotrophic growth reactors in which high turbidity and large variations in DO do not influence the species in the aquaculture pond, may offer a solution. In such a concept, the water treated in the external reactor is redirected to the pond while the release of microbial protein is controlled depending on the protein requirements by the culture species. The excess in microbial protein in the reactor can be harvested and used in other aquaculture units.