Physical plant for each hatchery is site-specific and its size depends on the desired production scale, the type of system and the availability of resources. Facilities may be simple or highly complex. The more complex physical plant encompasses the entire physical layout of the hatchery facility, including separate rooms for hatching and larval culture tank systems, feed preparation area including live feeds, dry laboratory space, an office, bathroom and auxiliary equipment. Most successful prawn hatcheries in Asia are 'backyard hatcheries' where the facilities include water storage, mixing and larval rearing tanks, as well as an aeration system, drainage facilities and a water supply system. Often, hatcheries are enclosed, to maintain controlled environmental conditions and to reduce contamination by insects and dust. However, many simple hatcheries are open, especially in tropical regions, where annual and diurnal temperature fluctuation is small.
The building housing the hatchery facility can be a greenhouse or a more permanent structure. In temperate and subtropical regions, hatcheries are enclosed in concrete/tile or insulated metal buildings (Valenti & Tidwell 2006), while in tropical regions hatcheries can also be of tile construction (Valenti 2007) or can be built of wood and roofed with leaves (Correia et al. 1988). With recirculation systems, excessive solar energy and light produces excessive heat during warmer months and encourages growth of algae, which can foul the tanks and biofilters. When production occurs in a greenhouse, the area above the culture tank should be shaded to provide a good indirect light and the biofilters and live food production areas should be covered completely. In more permanent structures, adequate windows should be made to provide proper lighting, such as presented in the layout by Aquacop (1983) and Valenti et al. (1998). Provisions for the availability of intense artificial light as back-up should be included (see also section 5.2.6). A typical flow-through hatchery diagram is shown in Figure 5.2.
An example of a recirculation prawn hatchery, the associated infrastructure and the economic analysis can be found in Fuller et al. (1992). This system is based upon the specifications given for a closed 'clearwater' system described in Daniels etal. (1992). Although each recirculation hatchery differs in size and configuration, commonalties include water preparation tanks, larval culture tanks with biofilters, feed preparation, live food culture systems and tanks for spawning and PL holding. The building needs a backup generator to operate the pump, air blower and heaters during any loss of electricity.
The design of any structure should allow for ease of disinfection to provide adequate larval health management. Normally, this includes a concrete floor and walls that are washable. Designs should minimise the amount of outside air (and contaminants) that is drawn through the building's venting system. Large fans in greenhouses, for example, run constantly during warmer months; this tends to draw in outside dust and potentially any agricultural chemicals being sprayed on adjacent areas. Buildings with self-contained heating and cooling systems minimise this risk, although it increases production cost.
All systems require water replacement, either daily or to replace water losses. Thus, each hatchery system requires additional tanks for water storage and preparation of brackishwater. Storage tanks may be square, rectangular or circular, but this depends solely on the characteristics of the site and local material costs. Commonly, storage
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