Tanks, Basins and Other Closed Production Units
The main purpose of a closed production unit is to create a restricted volume where the fish or other aquatic organisms can be fed in a good water environment. For fish, the units may be used from first feeding of fry up to on-growing. Closed production units are used for both freshwater and seawater species. A unit includes the water inlet, the production unit and the water outlet (Fig. 13.1).
To get a closed production unit to function as optimally as possible, a number of requirements can be set in addition to the main requirement that the unit should produce as much fish as possible at low cost. These are as follows:
· The supplied water, including the oxygen dissolved in the water, should be distributed evenly throughout the entire production unit
· The fish should be evenly distributed in the total production volume
· The fish must be transported effectively in and out of the unit
· The unit should require a minimum of manual cleaning
· The inner surface should be smooth and require little cleaning and maintenance
· The unit should be easy to operate, which means it should be easy to clean, to remove dead fish and to perform other handling fish tasks
The unit should have low investment costs per unit effective farming volume. This list shows that there are a number of requirements that need to be fulfilled before a production unit functions optimally. However, compromises have to be made because it is difficult to fulfil all requirements. For example, some species prefer to lie on the bottom and do not utilize the entire water column (non-pelagic species). The focus is on tanks with a circular flow and species that utilize the entire water column. However, there is a wealth of general information for all types of closed production units.
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