Aquaculture, the practice of farming fish and other aquatic species, is a rapidly growing industry that promises to meet the rising global demand for seafood. At the heart of this expansion is a technology that’s reshaping the industry: Recirculating aquaculture systems (RAS). These systems are efficient, sustainable and provide controlled environments that optimize fish growth and health. However, their success hinges on incorporating well-planned design strategies considering every detail, from water quality control to waste management.
Water Flow Dynamics
Correctly positioning inlets and outlets in RAS is crucial for maintaining optimal water flow. Water should enter the tank in a way that promotes uniform flow throughout the tank, preventing dead zones where waste can accumulate.
Positioning inlets at a height that introduces water into the tank with a spin creates a circular water flow pattern, or gyre, regardless of the tank’s shape. This gyre prevents the formation of stagnant areas, known as dead zones, where waste particles can accumulate. In addition, the angle and velocity of water entering the tank can be manipulated to optimize water circulation and distribute oxygen evenly throughout the tank.
Outlets should be positioned to remove waste-laden water efficiently, ideally at the tank’s lowest point, where waste typically settles due to gravity. This positioning enables the accumulation of residue to be directly suctioned out, preventing any build-up which could affect water quality and the health of the fish. In some designs, outlets might be positioned directly opposite the inlets, forming a gyre pattern. This pattern aids in sweeping waste toward the outlets, facilitating an effective and efficient waste removal process.
Construction Materials
The construction materials used for RAS tanks must be durable, non-toxic, and corrosion resistant. As these tanks often house fresh seafood species such as those used for sushi, it’s crucial to use materials that don’t contaminate the water with harmful substances. Despite their strength and durability, certain materials might release toxic compounds when corroded, posing a risk to the aquatic environment.
Reinforced Polyethylene (RPE) geosynthetic membrane liners are highly effective solutions for RAS production tanks to prevent the leaching of harmful substances and mitigate the risk of catastrophic leaks. These liners, renowned for their durability, non-toxicity, and corrosion resistance, are an ideal choice for RAS tanks. RPE liners are NSF/ANSI 61 certified for potable water containment, ensuring uncompromised water quality and the well-being of the aquatic harvest.
Moreover, these liners’ longevity and durability contribute significantly to RAS’s sustainability, aligning with the growing consumer demand for responsible and sustainable aquaculture practices. By implementing proactive measures in RAS design and operation, we pave the way for a future where fresh seafood, including sushi-grade fish, can be produced in an environmentally friendly and economically viable manner.
Determining Ideal Tank Configurations
Designing a recirculating aquaculture system (RAS) entails several considerations, among which the shape and size of the tanks play a crucial role. Specific factors that influence these decisions include:
- The species being farmed.
- Their growth rate and stage.
- The available space.
- The budget.
Species-Specific Requirements
The type of species being farmed significantly impacts the design of the RAS. For instance, species like trout that prefer flowing water are best suited to raceway systems, which mimic a river’s flow. Flatfish, however, typically reside at the bottom and can be accommodated in shallower, broad tanks. Additionally, the size and behavior of the species need to be considered. Larger, more active fish require more space and possibly different tank shapes than smaller, less active species.
Growth Rate and Stage
The growth stage of the fish is another crucial factor. Fry and fingerlings require smaller, separate tanks where they can be closely monitored and protected. They can be moved to larger tanks as they grow and graduate to different life stages. It’s crucial to plan for this progression when designing the system.
Space and Budget
The available space and budget will also influence the size and shape of the tanks. While larger tanks often offer better economies of scale, they require more space and higher initial investment. On the other hand, smaller tanks can fit into tighter spaces and may be cheaper to set up, but they might be less cost-effective in the long run due to higher costs per unit of production.
The shape of the tanks can impact fish behavior, water quality, and management efficiency. Round tanks are popular due to their self-cleaning nature— the circular water flow naturally carries solid wastes to the center of the tank, where they can be easily removed. However, rectangular tanks can be more space-efficient and fit better into some spaces.
One Tank, Two Tanks, Three Tanks... More?
When deciding between single large or multiple smaller tanks, consider disease control, stocking density, and ease of management. Numerous small ponds often allow for better disease control and easier management, as a disease outbreak in one pond can be quickly isolated and treated without affecting the others.
Then again, single, larger ponds may be more cost-effective in terms of space and resources and often permit higher stocking densities, enabling farmers to produce more fish with less water. However, they also require careful management of water quality parameters across the entire system, which can become very challenging if not monitored closely. Failure to do so can lead to disease or the accumulation of toxic compounds, contaminating the water and posing a risk to the fish and their environment.
Building a RAS is a complex task that requires careful planning and consideration of many factors. However, with the right design and construction, RAS can offer a sustainable and efficient solution for high-density fish farming.
