Classification of aquaculture
There are a number of ways to classify aquaculture facilities and production systems, based on the technology or the production system used.
‘Extensive’, ‘intensive’ and ‘semi-intensive’ aqua-culture are common ways to classify aquaculture based on production per unit volume (m3) or unit area (m2) farmed. Extensive aquaculture involves production systems with low production per unit volume. The species being farmed are kept at a low density and there is minimal input of artificial substances and human intervention. A low level of technology and very low investment per unit volume farmed characterize this method. Pond farming without additional feeding, like some carp farming, is a typical example. Sea ranching and restocking of natural lakes may also be included in this type of farming.
In intensive farming, production per unit volume is much higher and more technology and artificial inputs must be used to achieve this. The investment costs per unit volume farmed will of course also be much higher. The maintenance of optimal growth conditions is necessary to achieve the growth potential of the species being farmed. Additional feeding, disease control methods and effective breeding systems also characterize this type of farming. The risk of disease outbreaks is higher than in extensive farming because the organism is continuously stressed for maximal performance.
Salmon farming is a typical example of intensive aquaculture.
It is also possible to combine the above produc-tion systems – this is called semi-intensive aqua-culture. An example is intensive fry production combined with extensive ongrowing.
Another classification of an aquacultural system can be according to the life stage of the species produced on the farm, for instance eggs, fry, juvenile or ongrowing. Farms may also cover the complete production process, and this is called full production.
According to the type of farming technology used there are also a number of classifications based on the design and function of the production unit. This will of course be species and life-stage dependent. For fish the following classifications may be used: 1. Closed production units where the fish are kept in a enclosed production unit sepa-rated from the outside environment. 2. Open pro-duction units where the unit has permeable walls, such as nets and so the fish are partly affected by the surrounding environment. It is also possible to classify the farm based on where it is located: within the sea, in a tidal zone or on land.
Land-based farms may be classified by the type of water supply for the farm: water may be gravity-fed or pumped. In gravity systems the water source is at a higher altitude than the farm and the water can flow by gravity from the source to the farm. When pumping, the source can be at an equal or lower altitude compared to the farm. For tidal through-flow farms, water supply and exchange is achieved using the tide.
Farms can also be classified by how the water supplied to a farm is used. If the water is used once, flowing directly through, it is named a flow-through farm. If the water is used several times, with the outlet water being recycled, it is a water re-use or recirculating system.