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Water Quality Management

Fish farming has gained immense popularity over the years, primarily because it helps meet the growing demand for fish while addressing some of the negative impacts on the environment. Recirculating Aquaculture System (RAS) is a sustainable and efficient method of fish farming that is gaining popularity worldwide. In RAS, fish are grown in a closed-loop system, where water is continuously recirculated and treated, making it a more sustainable and eco-friendly method of fish farming. However, when recirculating the water, maintaining water quality is not only important for the health of the fish, but also important for the efficient operation of the farm. 

Importance of Water Quality Management in RAS Fish Farming

Maintaining the water quality is the highest priority in RAS fish farming. The fish are very sensitive to the water they are swimming in, and any fluctuations can lead to stress and/or disease, resulting in either poor growth or even worse: low survival rates. Therefore, it is essential to ensure that the water quality parameters are always within the desired range to ensure fish welfare.

Some of the water quality parameters important for fish wellbeing that need to be monitored in RAS farms include temperature, pH, salinity, dissolved oxygen, ammonia, nitrite, nitrate, alkalinity, hardness, and carbon dioxide. 

Other water quality parameters like turbidity or particle size and number are used as an indication of filter health. Many of these parameters can be monitored fully automatically with centralized systems such as the Lab Station from Blue Unit. Here are some of these parameters in detail:

  • Temperature: Temperature is an essential water quality parameter that affects fish growth and metabolism. In RAS farms, the water temperature should be maintained within a specific range, depending on the fish species. Most fish species thrive in water temperatures between 20°C to 30°C while others may prefer colder water such as Atlantic Salmon that prefer temperatures around 10-14 °C. Temperature is also an important parameter to measure because it interacts with many of the equilibriums in the water, such as how much oxygen that can be dissolved.
  • pH: The pH of the water indicates its acidity or basicity. The ideal pH range for RAS farms is between 6.8 to 7.8, depending on the fish species. Any fluctuations in pH can cause stress to the fish, leading to poor growth and increased mortality. High fluctuations in pH can also be an indication of low buffer capacity in the water. The pH is also an important parameter to understand the dynamics over devices.
  • Dissolved Oxygen: Fish require oxygen to survive, and dissolved oxygen is the oxygen present in the water. The dissolved oxygen levels in RAS farms should be maintained at least 5-7 mg/L. Any shortcoming from this range can lead to stress, reduced growth, poorer feed conversion, and mortality.
  • Ammonia: Ammonia is produced by fish waste and uneaten feed. High levels of ammonia are toxic to fish and can cause stress, gill damage, and death. In RAS farms, ammonia levels should be maintained below 1 mg/L.
  • Nitrite: Nitrite is produced by the breakdown of ammonia by nitrifying bacteria. High levels of nitrite are toxic to fish and can cause stress, reduced growth, and mortality. In RAS farms, nitrite levels should be maintained below 0.5 mg/L but can vary according to fish species.
  • Nitrate: Nitrate is produced by the breakdown of nitrite by nitrifying bacteria. High levels of nitrate can lead to poor growth and health issues in fish. In RAS farms, nitrate levels should generally be maintained below 100 mg/L but can vary according to fish species. 
  • Alkalinity: Alkalinity is the measure of the water’s ability to neutralize acids. Alkalinity helps to stabilize the pH in RAS farms. The ideal alkalinity level for RAS farms is between 70-200 mg/L.
  • Hardness: Hardness is a measure of the water’s mineral content, primarily calcium and magnesium. The hardness levels in RAS farms should be between 50-100 mg/L.
  • Carbon dioxide: Carbon dioxide is produced by fish respiration and bacterial activity. High levels of carbon dioxide can lead to stress and reduced growth in fish. In RAS farms, the carbon dioxide levels should be maintained below 20 mg/L but in some species the detrimental effects are already prevalent at around 10-12 mg/L.

It is crucial to monitor and maintain these water quality parameters to ensure the optimal health and growth of the fish. Failure to maintain these parameters can result in poor growth, increased mortality, and even disease outbreaks. But understanding water quality around the RAS farm is also key in managing system efficiency. Blue Unit Centralized analysis system set up for measuring gradients, can increase the knowledge of the water throughout the farm and help optimize the equipment’s performance.

Water Quality Management Techniques and systems in RAS Fish Farming

Here are the different techniques used to manage the water quality in RAS farms:

Filtration: Filtration is a critical component of water quality management in RAS farms. The filtration process removes suspended solids, uneaten feed, and fish waste from the water. The filtration system consists of mechanical filters, biological filters, and UV disinfectors.

Mechanical filters remove solid particles from the water through physical processes such as settling, screening, or centrifugation. Biological filters, on the other hand, remove dissolved nitrogenous compounds, such as ammonia and nitrite, through nitrification. UV sterilizers use ultraviolet radiation to kill harmful bacteria and viruses in the water.

Aeration: Aeration is the process of adding air to the water. Aeration pushes dissolved oxygen levels towards 100% saturation with air. This helps to remove gases that may be in excess (such as super saturation of nitrogen or too much oxygen). But more typically, aeration is useful to raise deficient oxygen levels, and remove toxic gases, such as CO2 or H2S. Aeration can be achieved with perforated tubing, diffusers, or air stones.

Monitoring: Monitoring the water quality parameters is crucial in RAS fish farming. The first line of defense against changes in the water quality starts with monitoring. Regular monitoring ensures that the water quality parameters are within the desired range. Monitoring can be done using different tools such as handheld meters, hanging sensor or ideally semi to fully automated monitoring systems.

Water exchange: Water exchange involves removing a portion of the water from the system and replacing it with fresh water. Water exchange can help to manage some water quality parameters within their desired range. However, excessive water exchange can lead to increased water usage, and dilution of beneficial components such as alkalinity, causing instability within the RAS farm. 

Carbon dioxide removal: Carbon dioxide removal is critical in RAS fish farming, as high levels of carbon dioxide can lead to stress and reduced growth in fish. Carbon dioxide can be removed from the water using degassing towers or air stripping and is done at the same time as oxygen replenishment as mentioned above.

Filtration systems

Filtration is a critical component of RAS fish farming, as it helps to remove waste and impurities from the water, ensuring optimal water quality for fish health and growth. There are several types of filtration systems that can be used in RAS farms, including mechanical filtration, biological filtration, and chemical filtration. To ensure optimal filtration in RAS farms, it is important to:

  • Choose the appropriate filtration system(s) for the specific fish species and farm size.
  • Monitor filtration efficiency regularly using appropriate equipment. A part of this is monitoring water quality changes across a given filter. 
  • Maintain filtration systems by cleaning or replacing filters as needed.
  • Implement redundancy and flexibility in filtration systems to ensure continuous operation.

Water flow management

Proper water flow management is essential for maintaining optimal water quality in RAS farms. Water flow helps to ensure sufficient aeration and circulation, which are critical for maintaining dissolved oxygen levels and removing waste from the water. To manage water flow in RAS farms, it is important to:

  • Optimize system design to ensure appropriate water flow rates, avoid dead zones and facilitate efficient waste removal. Monitoring water quality on either side of a device is enough to detect water flow issues. 
  • Use appropriate pumps and other equipment to maintain optimal water flow.
  • Monitor water flow using appropriate equipment. 
  • Implement redundancy in water flow systems to ensure continuous operation.

Fish stocking density

The stocking density of fish in RAS farms can have a significant impact on water quality and fish health. Understocking can lead to sedimentation of waste within a fish tank, potentially causing rapid water quality issues and greater challenges for filtration systems. Overcrowding can directly cause water quality problems and increase the risk of disease outbreaks. It can also cause fish aggression issues. To manage fish stocking density in RAS farms, it is important to:

  • Determine the appropriate stocking density based on the specific fish species, age, and size.
  • Monitor fish growth and adjust stocking density as needed.
  • Use appropriate management techniques, such as grading or thinning, to ensure optimal fish health and growth.
  • Avoid overstocking by maintaining appropriate stocking densities for the specific fish species and farm size.

You can feel confident that the fish environment is under the best surveillance, by knowing your gas composition throughout your farm with Blue Unit Lab Station centralized system.

Feed management

Proper feed management is crucial for the health and growth of fish in RAS farms. Accidental overfeeding is a disaster for water quality. Likewise, poor quality feed can lead to excessive feeding without fish nutritional requirements being met. Underfeeding, on the other hand, can lead to malnourishment and greater aggression within the population with long lasting regrettable results like fin damage. To ensure optimal feed management in RAS farms, it is essential to:

  • Determine the appropriate feeding rate based on the fish species, age, size, and water temperature.
  • Use high-quality feeds that are highly digestible, nutritionally balanced for the specific fish species. Monitoring water quality across the RAS farm is a useful tool to detect poor feed performance. 
  • Monitor feed intake and adjust feeding rates as needed to ensure optimal growth without over feeding.
  • Avoid overfeeding. Again, closely monitoring water quality is an important tool in determining how much to feed on a given day, or alert to over feeding. For example, if water quality is poor, the manager should not feed out the theoretical ration. But if the normal ration is given despite repressed fish appetite, then water quality monitoring will alert to a worsening culture environment for the fish. 

With Blue Unit TurbiFlex, turbidity changes can easily be discovered and counteractions on overfeeding can be made. Even poor feed quality can be picked up by the Online Turbidity measurements.

Disease prevention

Disease outbreaks can have a significant impact on the health and productivity of fish in RAS farms. To prevent disease outbreaks in RAS farms, it is essential to:

  • Implement a quarantine protocol for new fish entering the system.
  • Implement biosecurity measures to prevent the introduction and spread of pathogens, such as controlling access to the farm, disinfecting equipment, and maintaining strict sanitation protocols.
  • Monitor fish health regularly and respond promptly to signs of illness. Have water quality values available for veterinary staff, so they can potentially match a past adverse culture environment with a clinical sign.  
  • Manage fish stress factors such as water quality, fish density and apply appropriate husbandry techniques. 
  • Manage filtration systems to avoid disease causing reservoirs. A better managed biofilter or well-maintained UV system will be better at managing an offensive biological or chemical agent.

Waste management

RAS farms generate significant amounts of waste, including uneaten feed, fish feces, and other organic matter. Proper waste management techniques, such as solids removal and anaerobic digestion, can help to reduce the environmental impact of RAS farms. To manage waste in RAS farms, it is essential to:

  • Manage water exchange downwards. Minimizing the volume of water leaving the farm implicitly means that waste leaving the farm is more concentrated. More concentrated waste means more cost-effective waste treatment. 
  • Implement a solids removal system, such as a settling tank or drum filter, to remove uneaten feed and fish waste from the water.
  • Treat solids removed from the water using anaerobic digestion to produce biogas and fertilizer.
  • Use treated waste material as fertilizer for crops or other uses.

Energy efficiency

RAS farms require significant amounts of energy to operate the various systems involved in water quality management. In turn, monitoring water quality is fundamental for optimizing energy use. 

Implementing energy-efficient practices, such as using high-efficiency pumps and optimizing system design, can help to reduce the energy consumption and associated costs of RAS farms. To improve energy efficiency in RAS farms, it is essential to:

  • Optimize system design to minimize energy consumption, such as using gravity flow systems or reducing the number of pumps required. 
  • Optimizing future system design starts with understanding today’s system design, with water quality monitoring playing a large role in understanding. 
  • Use high-efficiency pumps, blowers, and other equipment. 
  • Use water quality monitoring to reduce water or air exchange, directly minimizing energy use for temperature regulation.
  • Monitor water quality on either side of each water treatment device to detect operational problems and inefficiencies. 
  • Implement a control system to manage energy consumption and optimize system performance.

Monitoring and control systems

To ensure optimal water quality and fish health in RAS farms, it is essential to have effective monitoring and control systems in place. These systems can help to detect and respond to water quality issues quickly, minimizing the impact on fish health and productivity. To implement effective monitoring and control systems in RAS farms, it is important to:

  • Choose appropriate monitoring and control systems for the specific farm size and equipment. 
  • Install sensors and monitoring equipment in critical locations, such as in tanks, on filtration systems and aeration systems. Remember some sensors drift and/or require maintenance for reliable operation. Make a risk analysis for the fish farm sensor program. 
  • Use appropriate control systems, such as programmable logic controllers (PLCs), to automate system operations.
  • Train staff on maintenance, monitoring and control procedures and regularly review system performance.

Having knowledge about your water quality is important for all farm operations. Blue Units’ various solutions for analysis and data collection are invaluable tools for increasing plant performance leading to optimal growing conditions for fish.

To summarize

Water quality management is critical in RAS fish farming to ensure the optimal health and growth of the fish. Regular monitoring of water quality parameters, filtration, aeration, water exchange, and carbon dioxide removal are some of the techniques used to manage water quality in RAS farms.

It is essential to understand the specific requirements of the fish species being farmed and ensure that the water quality parameters are maintained within the desired range. With proper water quality management techniques in place, RAS fish farming can be a sustainable and efficient method of fish production that minimizes the negative impact on the environment.

Blue Unit’s various product and services are constantly developed to meet you and the fish’s requirements.