Environmental management in RAS: A guide to optimizing cultivation

Recirculating Aquaculture Systems (RAS) represent the forefront of aquaculture production. Their ability to operate at high densities, year-round, and with superior environmental control positions them as a sustainable and efficient solution. However, the success of these systems lies not only in their infrastructure but in the precise management of environmental factors to meet the needs of the species at every stage of their development.

A recent scientific review article published by researchers from Jiangsu University delves into how key design and operational parameters of RAS—from light and temperature to disinfection and water quality—directly influence the physiological and behavioral responses of aquatic animals. Understanding these interactions is fundamental for any producer seeking not only to maximize yield but also to ensure the welfare of their organisms.

Key findings

• The precise control of factors such as light, temperature, and water quality is decisive for productive efficiency and profitability in RAS.
• Manipulating light (intensity, spectrum, and photoperiod) can promote growth and reduce stress if adapted to each species and its developmental stage.
• The constant noise from equipment in a RAS can be a stressor that negatively affects growth and immunity, whereas stimuli like music can have positive effects.
• Each water parameter (flow, dissolved oxygen, salinity, pH, and nitrates) has an optimal range that, when maintained, maximizes growth and animal welfare.

The impact of light: More than just illumination

Light is one of the most influential environmental factors and, fortunately, one of the easiest to control in a RAS. It’s not just about a day-and-night cycle; intensity, spectrum (color), and photoperiod have profound effects. The study highlights how LED lighting systems, thanks to their low cost and adjustability, are becoming the “green light source” of modern aquaculture.

• Light color: For largemouth bass, blue and green light promoted growth and improved oxidation resistance, while red light was detrimental. In contrast, Pacific pollack showed a strong attraction to dark, red, or orange environments, avoiding short-wavelength lights like green or blue.
• Intensity: Juvenile starry flounder gained 36% more weight under low light intensity (15 lx) compared to high intensity (2500 lx), which was associated with higher daily feed intake.
• Photoperiod: For Pacific white shrimp, 24 hours of supplementary light per day resulted in the highest growth rate and individual weight gain. Conversely, for coho salmon, operating under 24 hours of continuous light showed no significant behavioral differences compared to a cycle of 12 hours of light and 12 hours of darkness, suggesting an opportunity to increase yield.

These findings demonstrate that there is no one-size-fits-all solution. The optimal lighting strategy must be based on specific studies for each species and its life stage.

Sound in cultivation: Stressful noise or beneficial melody?

An often-underestimated aspect of RAS is the acoustic environment. The constant operation of pumps, aerators, and filtration systems generates persistent underwater noise that can impact the animals.

The problem with noise

The study reports that juvenile largemouth bass exposed to typical RAS noise (115 dB) gained 55% less weight than the control group. This noise also negatively affected their antioxidant and immune systems and altered their swimming behavior, making it more dispersed. Particularly, low-frequency noise (80-1000 Hz) proved to be the most harmful, inhibiting growth and collective feeding. However, the response is not universal. Studies on Pacific white shrimp and Atlantic salmon found no measurable negative effects, possibly due to rapid adaptation or a higher hearing threshold in hatchery-reared individuals. Rainbow trout, although showing slower growth in the first month under high-noise conditions, gradually adapted and showed no significant differences after five months.

The potential of music

In contrast, music can promote welfare and growth. In an experiment with Koi fish, musical stimuli such as Sufi Ney music or a Quranic recitation, played three times a day, had a positive effect on growth and feed efficiency. Mozart’s classical music also proved to be a potential stress mitigator for common carp.

Temperature: A determining factor for metabolism and growth

Water temperature is one of the most critical factors, as it directly influences the metabolism, appetite, growth, and reproduction of aquatic animals. The ability of RAS to maintain a constant, optimal temperature is one of its greatest advantages.

• For Nile tilapia fry, the optimal temperature was found to be 28°C, where they grew nearly twice as fast as at 24°C or 32°C.
• Red-spotted grouper showed higher feeding and digestion activity at 25°C.
• Temperature control even enabled a reproductive milestone: the first controlled natural spawning of American shad was achieved in a RAS by manipulating temperature regimes to simulate seasonal cycles.

Finding the optimal temperature is crucial, but it must always be balanced with the system’s energy consumption to ensure economic viability.

Disinfection methods: A balance between safety and efficacy

The high density and water recirculation in RAS create an environment conducive to the proliferation of pathogens. Therefore, effective disinfection is indispensable.

• UV disinfection: This is a physical method that leaves no chemical residue. However, its effectiveness depends on water clarity (turbidity reduces it), and it has no residual effect, meaning microorganisms can recover. Nevertheless, UV treatment has been shown to improve the growth rate of juvenile Atlantic cod and reduce bacterial concentration by 90%.
• Ozone: It is a potent disinfectant, but its use requires strict control, as ozone residuals are toxic to the farmed animals and can affect biofilters. For Pacific white shrimp, a concentration of 0.06 mg/L was recommended as the maximum safe level, sufficient to control bacterial biomass without causing harm.
• Other chemical disinfectants: Hydrogen peroxide and peracetic acid are “green” options that can control pathogens at low concentrations, but care must be taken not to affect the nitrifying bacteria in the biofilter. Sodium chloride (salt) is effective, but its use increases costs and the system’s salinity.

The aquatic environment: Water flow and quality

Water is the medium where the animals live, breathe, and feed. Its management is, therefore, the cornerstone of a RAS.

Water flow

An appropriate flow velocity promotes growth and morphological uniformity in species like salmon. For tilapia, continuous swimming at speeds of up to 2 BL/s (body lengths per second) improved their growth performance. However, excessive flow can be detrimental; juvenile pollack tend to avoid areas of strong current. The goal is to find a balance that encourages exercise without causing stress or excessive energy expenditure.

Water quality

• Dissolved oxygen: Low levels reduce feeding and growth rates, while excessively high levels can cause oxidative stress.
• Salinity: Maintaining optimal salinity reduces the energy fish expend on osmoregulation, allowing more energy to be allocated to growth. Juvenile black sea bass, for example, showed higher growth performance at an intermediate salinity of 13 g/L.
• pH: The pH in a RAS tends to decrease due to fish respiration and nitrification. Its control, either through CO₂ degassing or the addition of alkaline solutions, is vital.
• Nitrate: Although considered less toxic than ammonia or nitrite, the accumulation of nitrate (NO3−​−N) can cause chronic toxicity. For juvenile rainbow trout, high concentrations (80−100 mg/L) decreased survival and increased abnormal behaviors.

Conclusion: Towards integrated, data-driven management

Optimizing Recirculating Aquaculture Systems is a complex yet achievable challenge. As this review demonstrates, each environmental factor plays a crucial role in the health and productivity of the cultivated species.

The future of successful and sustainable RAS depends on moving away from a single-factor approach and toward integrated management. More research is needed on the interactions between multiple factors, the long-term effects throughout the entire life cycle, and the development of species-specific databases. By combining biology, ecology, and engineering, and with the help of technologies like artificial intelligence to model these complex interactions, RAS can evolve into adaptive ecosystems that fulfill their promise of being the cornerstone of sustainable aquaculture.

Contact
School of Agricultural Engineering, Jiangsu University
Zhenjiang, Jiangsu 212013, China
Email: cwli@ujs.edu.cn

Reference (open access)
Dai, L., Chen, Y., & Li, C. (2025). Environmental factor impacts on behavioral and physiological responses of aquaculture species in recirculating aquaculture systems: Mechanisms and regulation. Aquaculture Reports, 44, 103036. https://doi.org/10.1016/j.aqrep.2025.103036

Milthon Lujan

Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.