Biotechnology in Agriculture and Aquaculture

This note covers aquaculture-specific biotechnology. Bt cotton and Golden rice, biotechnology's established applications in crop agriculture, are covered in Microbes, Immunity and Modern Biotechnology.

Recirculating Aquaculture Systems: biology and physical filtration doing separate jobs

A Recirculating Aquaculture System (RAS) grows fish in a closed, continuously reused water system rather than an open pond, and it depends on two genuinely different treatment steps working together rather than one filter doing everything.

Physical filtration components remove solid waste, uneaten feed and faecal matter, straining it directly out of the water. The biofilter handles a problem physical filtration cannot: the toxic ammonia that fish themselves excrete as a metabolic waste product, which builds up steadily in a closed, recirculated system with nowhere for it to disperse. The biofilter hosts colonies of nitrifying bacteria that convert this toxic ammonia first into nitrite and then into nitrate, a far less harmful compound, through the biological process of nitrification, the same underlying bacterial process a municipal sewage treatment plant's secondary treatment stage relies on. What a biofilter is not used for is deliberately adding phosphorus to encourage plankton growth as supplementary feed; excess nutrient build-up, phosphorus included, is something RAS operators actively work to manage and remove, not something they deliberately introduce.

Biofloc technology: turning waste into feed instead of removing it

Biofloc technology (BFT) takes a related but distinct approach: rather than only converting or removing waste, it actively converts fish waste and uneaten feed into a protein-rich biomass the fish can then eat. A mix of beneficial bacteria, added along with a carbon source such as molasses, breaks down the organic waste and toxic nitrogen compounds in the tank and rebuilds them into microbial biomass "floc" suspended in the water, which growing fish and shrimp consume directly as supplementary feed.

The practical payoff is a dramatic gain in land efficiency: farmers using biofloc tanks can produce roughly 2,000 kilograms of fish from just four small tanks covering about 150 square metres, an output that would need around 4,000 square metres of conventional pond space to match. The system also keeps water cleaner for longer without frequent water changes and reduces disease risk, since the closed, actively managed tank environment limits farmers' reliance on external chemicals or antibiotics.

Quick revision points

• A Recirculating Aquaculture System (RAS) uses physical filtration for solid waste and a biofilter (nitrifying bacteria) for toxic ammonia, converting it via nitrification into far less harmful nitrate. Biofilters are not used to deliberately add phosphorus for plankton growth; excess nutrients are managed and removed, not encouraged.
• Biofloc technology (BFT): uses beneficial bacteria plus a carbon source (e.g. molasses) to convert fish waste directly into protein-rich biomass the fish themselves eat, rather than merely removing the waste.
• Biofloc's land efficiency is dramatic: roughly 2,000 kg of fish from four small tanks (~150 sq. m), versus ~4,000 sq. m of conventional pond space for similar output.
• Bt cotton and Golden rice, biotechnology's established applications in crop agriculture, are covered separately in Microbes, Immunity and Modern Biotechnology.