1.1 Aquaculture engineering
During the past few years there has been considerable growth in the global aquaculture industry. Many factors have made this growth possible. One is developments within the field of aquaculture engineering, for example improvements in technology that allow reduced consumption of fresh water and development of re‐use systems. Another is the development of offshore cages: sites that until a few years ago not were viable for aquaculture purposes can be used today with good results. The focus on economic efficiency and the fact that salaries are increasing have also resulted in the increased use of technology to reduce staff numbers.
The development of new aquaculture species would not have been possible without the contribution of the fisheries technologist. Even if some techniques can be transferred for the farming of new species, there will always be a need for technology to be developed and optimized for each species. An example of this is the development of production tanks for flatfish with a larger bottom surface area than those used for pelagic fish.
Aquaculture engineering covers a very large area of knowledge and involves many general engineering specialisms, such as mechanical engineering, environmental engineering, materials technology, instrumentation and monitoring, and building design and construction. The primary aim of aquaculture engineering is to utilize technical engineering knowledge and principles in aquaculture and biological production systems. The production of fish has little in common with the production of nails, but the same technology can be used in both production systems. It is therefore a challenge to bring together both technological and biological knowledge within the aquaculture field.
1.2 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’ 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 production systems and this is called semi‐intensive aquaculture. An example is intensive fry production combined with extensive on‐growing. Aquacultural systems can also be classified according to the life stage of the species produced on the farm, for instance eggs, fry, juvenile or on‐growing. Farms may also cover the complete production process, and this is called full production.
Depemding on 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 an enclosed production unit separated from the outside environment; (2) open production units, where the unit has permeable walls (e.g. 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‐fed systems the water source is at a higher altitude than the farm and the water flows by gravity from the source to the farm. In pumped systems, the source can be at an equal or lower altitude compared with the farm. For tidal through‐flow farms, water supply and exchange are 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 system. If the water is used several times, with the outlet water being recycled, it is a water re‐use or recirculating aquaculture system (RAS). It is also possible to separate production systems as monoculture or polyculture: monoculture involves the production of only one species (e.g. fish), whereas polyculture involves the production of two or more (e.g. fish and rice). This is also named ‘integrated aquaculture’.