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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)
The main goal of any aquaculture system is to produce, grow and sell fish or other aquatic animals and plants. The basic situation of fish rearing is shown in Figure 2. Fish living in a water body receive feed and oxygen. Their metabolism converts these into excreta and CO2 which, if they accumulate in the water, are toxic for the fish. Different fish farming technologies cope with this problem using different strategies.
Figure 2: The basic principle of aquaculture from a water perspective. Fish living in water receive feed and oxygen. Their metabolism converts these into excreta and CO2, which are toxic for the fish. The water becomes waste water
Aquaculture systems can be classified into four basic types: fish ponds, net-enclosures, flow-through, and recirculation systems (Figure 3). 'Open' aquaculture techniques such as net enclosures and flow- through systems release nutrient-rich wastewater into the environment, potentially causing eutrophication and oxygen deficiency in water bodies. In recirculating aquaculture systems (RAS) this waste water is treated and re-used within the system.
RAS has several advantages when compared to other aquaculture systems: it is a totally controlled system that is largerly independent of local conditions; it has very low water usage with low wastewater flows; and production can be planned and targeted year-round. However, there are also disadvantages, such as significant investment and operation costs, and high operation risk due to failure-prone technology. Species selection is therefore limited mostly to carnivores, which command a higher market price than herbivores, and the system is utterly dependent on artificial feeds (see Chapter 4). In this context, aquaponics can be viewed as a form of RAS or an extension of RAS. Therefore, in this chapter, the aquaculture part of a recirculating aquaponic system is presented in more detail.
Figure 3: The main types of aquaculture systems
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