AQUACULTURE
Recirculating aquaculture system (RAS) technology
A recirculating aquaculture system (RAS) consists of fish tanks and several filtration units which clean the water. In a classic RAS the water is thereby in constant flow from the fish tanks through the filtration system and then back to the fish tanks (Figure 4). Due to the metabolism of the fish, the water that leaves the tanks contains high concentrations of solids, nutrients, and carbon dioxide, whilst it is oxygen-poor compared to inflowing water.
· Aqu@teachPlanning the recirculating aquaculture part for an aquaponic system
In aquaponics, it is very important that the input and output of nutrients is in balance over the entire plant growing period. This balance can mainly be controlled using two different approaches: Approach 1: An existing recirculating aquaculture system (RAS) is used to dimension the corresponding hydroponic unit with plants (Figure 12). This approach is covered by the Exercise in Module 5 (nutrient water balance). Approach 2: The RAS is dimensioned based on the desired plant and fish production (Figure 13).
· Aqu@teachManagement of recirculating aquaculture system (RAS)
Stocking density Stocking density is a very important factor that has to be decided in advance when designing a RAS. Stocking density can be defined in different ways (Table 2), and it is important to be aware when and why different definitions are being used. Table 2: Stocking density definitions Density of individuals Biomass density per surface (#/m2) per volume (#/m3) per surface (kg/m2) per volume (kg/m3) Independent of tank depth.
· Aqu@teachIntroduction to aquaculture
Aquaculture is the captive rearing and production of fish and other aquatic animal and plant species under controlled conditions (Somerville et al. 2014). Due to overfishing and the consequent decline of wild fish stocks, aquaculture has become increasingly important in the past few decades (Figure 1), and may become even more so in the future as wild fish stocks face immense pressure from climate change (Gibbens 2019). Figure 2: In 2016 aquaculture accounted for around 47% of total global fish production (FAO 2018)
· Aqu@teach