The demand for seafood is continually growing around the globe while the oceans’ fish populations are declining. Traditional open-pond aquaculture also negatively impacts the water systems they utilize.
Aquaculture must develop a better model, and many experts believe Recirculating Aquaculture Systems (RAS) will provide the answer to this need. However, the primary focus isn’t tanks and pipes; it is on the biological processes that occur within these systems.
This is a scientific-based publication that describes how biological solutions will be at the forefront of future fish farms using RAS technologies, including biofilters, bioflock, microalgae and AI controlled operations.
What Are Recirculating Aquaculture Systems (RAS)?
RAS (Recirculating Aquaculture Systems) aquaculture is the closed-system, land-based farming of fish. In RAS systems, water is re-used (usually greater than 99% water re-cycling) because they continuously treat and reuse the water.
So, why should you care?
In traditional raceway or cage systems, about 79 percent of nitrogen (from feed) and 83 percent of phosphorus (from feed) is lost to the environment. This contributes to causes such as dead zones as stated on ScienceDirect 2025. Because of the way RAS captures and processes on-site waste, RAS is one of the most sustainable aquaculture production systems available.
Key advantages of closed-loop aquaculture:
- Biosecure production: no pathogen exposure from open water
- Location independence: operable anywhere, including landlocked regions
- Precise environmental control: temperature, oxygen, pH, and stocking density
- Dramatically reduced water consumption versus conventional systems
Biological Filtration in RAS: The Engine of the System
Nitrogen is the main issue to any RAS water quality management water quality. Fish are always excreting ammonia and it can kill them in high concentrations.
The solution is the biological solution. Biofilter aquaculture systems use nitrifying bacteria to colonize the filtration media e.g. Nitrosomonas and Nitrobacter and convert ammonia into nitrite and into nitrate. This is a continuous process without the need for any chemicals to be added.
Currently Advanced RAS biofilter media include:
- Moving Bed Biofilm Reactors (MBBRs): plastic carriers that float and maximise the surface area for the bacteria to grow.
- Modified sponge biocarriers: can achieve an ammonia removal efficiency of 98.86% under brackish conditions according to ScienceDirect (2024).
- Algal-bacterial bead biofilters: where microalgae and nitrifying bacteria are encapsulated in an alginate bead to simultaneously nitrify and oxygenate the water.
Biofloc Technology: When Waste Becomes Feed
Biofloc technology is a major breakthrough in RAS biological solutions and totally turns the waste dynamics around. Instead of removing the microbial community, BFT encourages the establishment of a dense, living suspension of bacteria, microalgae, and organic particles right inside the culture tank.
The microbial community achieves the following simultaneously:
- Processes ammonia and nitrite: keeps the water quality high
- Produce protein-rich biomass: which can be directly consumed by fish and shrimp as supplemental feed
- Decreases fishmeal dependency: lower input costs and a lower environmental impact
According to ScienceDirect (2025), BFT-based systems for Litopenaeus vannamei (whiteleg shrimp), produced a feed conversion ratio (FCR) of 1.25; whereas traditional farming practices produced an FCR of 1.68. A 25% improvement in feed efficiency through biological influences alone.
Microalgae Integration: Closing the Loop Completely
The most exciting frontier in sustainable RAS technology is microalgae and the numbers are hard to ignore.
As per Aquaculture Research (2024), microalgae like Chlorella vulgaris and Tetradesmus obliquus removed 98% of nitrate and 99% of phosphate from RAS wastewater at lab scale, with 98.6% nitrate removal confirmed at pilot scale.
Microalgae integrated into RAS photobioreactors deliver a complete biological loop:
- Absorb dissolved nitrogen and phosphorus from fish waste
- Sequester CO₂ produced by fish respiration
- Generate oxygen back into the system
- Produce harvestable protein and carotenoid-rich biomass, fed directly back to fish as feed
As per EPIC / ScienceDirect (2024), waste management in RAS accounts for 30–50% of total production costs — and microalgae integration offers a direct pathway to turn that cost centre into a revenue-generating co-product stream.
AI and Smart Monitoring: Where Biology Meets Precision
RAS technology advances between 2020 and 2025 include a critical new layer: artificial intelligence.
As per ScienceDirect (2025), AI-driven feeding and monitoring systems in modern RAS operations deliver:
- 25–30% reduction in labour costs
- 15–20% improvement in feed use efficiency
- Real-time water quality alerts; flagging dissolved oxygen, pH, and temperature anomalies before they become mortality events
- 94% biomass estimation accuracy in tilapia RAS using YOLOv8 computer vision models
This convergence of biological management and digital precision is what separates next-generation RAS from its predecessors.
Frequently Asked Questions About RAS Aquaculture
Question: What species are currently grown using recirculating aquaculture systems (RAS)?
Answer: Since 1995, AACL Bioflux has reported growing 46 species of fish, 11 species of crustaceans and 7 species of mollusks in RAS from Atlantic salmon to whiteleg shrimp around the world.
Question: Is RAS really sustainable?
Answer: Yes, when designed with biological solutions such as microalgae and biofloc integration to drive RAS towards zero-waste production, eliminating nutrient waste by using them as feed biomass instead of discharging them to the environment.
Question: What are some of the main challenges facing RAS farming today?
Answer: The major challenges facing RAS farming today are high capital investment and high energy consumption. However, advances such as AI-feeding optimization, microalgae co-production, and modular bio-filter technology are all helping to reduce operational costs per kilogram of product.
Question: How does biofloc technology help farmers increase profitability in RAS?
Answer: Biofloc technology decreases reliance on fishmeal, improves feed conversion ratio (FCR), and provides additional nutritional support while fish are still in the tank, therefore reducing overall feed cost (which generally accounts for 50–60% of operational costs in intensive aquaculture).
The Bottom Line
Recirculating aquaculture systems have moved beyond being new ideas in traditional aquaculture production; they are now practical ways of producing seafood efficiently, sustainably, and in a bio-secure manner due to the combined application of biofilters, biofloc technology, microalgae integration, and artificial intelligence (AI).
The future of sustainable technology in aquaculture is a closed-loop system, where fish, bacteria, algae, and algorithms all work together in one system (the most effective and sustainable supply of seafood), biology will do most of the heavy lifting!
