1.2.3 The physical plant

Careful thought should be given to hatchery design to permit convenient and efficient operations. The hatchery should be adaptable so that changes can be made readily without involving major rebuilding. In some hatcheries, tanks have been constructed of concrete and changes cannot be made easily. It is much better to have plastic or fibreglass tanks so they can be easily moved or changed if needed. Floors should be of concrete and have sufficient drains. All surfaces should be covered with a durable, mildew resistant finish to facilitate cleaning.

Floor standing cabinets and storage units made from wood should be mounted on concrete plinths to prevent them being damaged by immersion in seawater. Where this is not possible, wood surfaces need to be painted with a good quality epoxy resin.
A hatchery has several areas that are all inter-related. For convenience they have been divided into algal culture, broodstock conditioning and spawning, larval rearing, juvenile culture and service areas (Figure 5).

Figure 5: A generalized floor plan for a purpose-built bivalve hatchery (see the following text for explanation).

1.2.3.1 Algal culture facility

The success of a bivalve hatchery depends on the production of algae. Large quantities of high quality algae must be available when needed. It is a most important part of any hatchery and considerable thought should be given to providing a sufficient and efficient working area for this purpose (AC – Figure 5). Since algae are used in all phases of production, the facility should be located centrally and conveniently. Space required for algal culture depends partly on levels of production, methods of culture and whether algae will be raised entirely inside the hatchery with artificial illumination, or if it will be raised outside under natural light, or a combination of the two. A well ventilated greenhouse is required if algae is grown in natural light and this structure needs to be placed so as to obtain the maximum amount of sunlight. Shading may be need to protect younger, less dense cultures from strong sunlight.
A small room is required to maintain stock (also known as master) cultures of algae (TR). Dimensions vary but it can be as small as 2 x 3 m. The room should be insulated and the temperature kept cool. Shelving is needed with flourescent lights at the back to provide the light source. An air supply is also required. Test tubes with algal slants and small flasks with stock culture that are monospecific and axenic are kept in this room often in a refrigerated, illuminated incubator. Methods are described in a Part 3.
The next phase of culture uses stock cultures from the cool room and grows them in 4 l flasks and 20 l carboys against a bank of fluorescent lamps (SCR). This can be part of the main algal culture area or a small room off it. The space required depends on the number of species and amount of algae being produced. This area requires an air and carbon dioxide supply and needs to be kept at 15 to 18oC. Another adjacent small room (AR) houses an autoclave (a), which is used to heat sterilize medium for the small cultures. Some hatcheries use alternative methods to prepare culture medium and these are described in Part 3.
The size of the main algal culture area depends on the number of species being cultured and the amount of algae required. This area can occupy a substantial part of the hatchery. If most of the algae is raised inside the hatchery by the batch culture method then there must be sufficient space for a series of tanks that can measure up to 3-4 m in diameter and 2 m in depth. If the bag or tall cylinder culture methods are used the amount of floor area required can be reduced. Ballasts for fluorescent lamps used to illuminate cultures need to be of the “cool running” type or isolated in a separate area from which the heat they generate can be dissipated. This area should ideally be maintained at 15 to 20oC.
In many hatcheries, considerable portions of the algae, if not all, are raised in greenhouses. These can be stand-alone structures or attached to one side of the hatchery - preferably the south side in the Northern Hemisphere and northern side in the Southern Hemisphere, so as to receive as much sunlight as possible. The size of the greenhouse depends on the method of culture and quantities of algae that need to be produced.
Sufficient electrical power must be available for artificial lighting when natural sunlight is inadequate. Compressed air and carbon dioxide supplies are essential. There should be adequate ventilation or installed air-conditioning to maintain temperatures at or below 20°C on days when bright sunlight heats the facility. A generator will be required in areas where the electricity supply is unreliable and may be off for several hours or more at a time. Although survival of the algal cultures is not at risk in the absence of light for an hour or two, cultures need to be aerated. Diatoms will settle to the bottom of cultures without aeration and cultures may collapse.

1.2.3.2 Broodstock holding and spawning area

Space is required to hold and condition broodstock (BC – Figure 5). The amount of space needed depends in part on the number of species being held and whether some or most of the conditioning will be undertaken in the open environment rather than in the hatchery. Heated or chilled seawater may be required for this aspect of operation at certain times of the year. The ability to isolate tanks so that photoperiod can be adjusted is desirable since it has been shown that varying periods of light and dark can affect gonadal maturation.
Space is required for spawning trays (sp) but this can be part of the larval rearing area since the space is not require continuously. Spawning trays or dishes can be stored when not in use. Methods for broodstock conditioning, spawning and fertilization are described in Part 4.

1.2.3.3 Larval culture area

Another major part of the hatchery is occupied by the larval rearing facility (LC) and dimensions of this area depend on the scale of production. The space is occupied with tanks, the number needed depending on production levels and the techniques used to rear larvae. On the Pacific coast of North America the tendency has been to raise larvae at low densities of 2-3 per ml in large tanks that measure 3-4 m in diameter, 4-5 m in height and hold 40 000 to 50 000 l. In other hatcheries larvae are raised in smaller tanks of up to 5 000 l in volume at higher larval densities. A manager must decide on required production to meet market demand and the methodology that will be used to rear larvae when planning this part of the hatchery.
Larval rearing tanks are generally made of fibreglass or of a suitable plastic and should be thoroughly leached prior to use. Regardless of the size of tanks used, there should be large sunken floor drains to handle large volumes of water when the tanks are drained. A preparation area in the larvae culture room (P) is required for washing, grading, counting and measuring larvae and for accommodating the equipment used for these purposes. This area requires cupboards and shelves for the storage of equipment when not in use.

1.2.3.4 Juvenile culture area

Once mature larvae have set (settled and begun metamorphosis) they are moved to tanks in the juvenile culture room (JC) for culture until they are of sufficient size to transfer to nursery systems, which may be part of the hatchery or at another location. This is generally when the juveniles (known as spat) exceed 2 mm shell length. The size and types of tanks in terms of volume and surface area used for this purpose vary according to species.
Mature larvae are set in the hatchery or in outside (sometimes remote) facilities. When this procedure occurs within the hatchery it is generally done in the larval culture area, frequently directly in the larval tanks. Space for additional tanks may be required specifically for this process. Spat (early juveniles) are subsequently transferred to tanks systems in a separate area specifically for juvenile culture (JC). The size and types of tanks in terms of volume and surface area used for this purpose vary according to species. They may be upwellers, downwellers or tray systems of varying configuration and the juveniles are grown in these until they exceed 2 mm shell length. To grow spat to a larger size within the hatchery on cultured food is uneconomic since food requirement increases exponentially with size. If the nursery system is located outside the hatchery, sufficient space must be allotted for this operation.
Methods for the culture larvae are described in Part 5 and for spat in Part 6.

1.2.3.5 Other space requirements

Hatcheries dealing with broodstock from outside the immediate region or with exotic species may, as already mentioned, be required to quarantine stock and rear the progeny in isolation. Such hatcheries will include a quarantine room (QR) for this purpose, the effluent from which is discharged into treatment tanks (ET).
Other rooms include a dry laboratory (DL), office (O) and bathroom (BR). The dry laboratory is where algal transfers can be made (if no specific space is allocated elsewhere), chemicals weighed and mixed, microscopes kept for examining cultures, records maintained and for the storage of scientific equipment.
Static machinery such as the main pumps, sand filters and pre-filters (to remove particles down to 10 ?m), seawater heating/chilling units, furnaces, the air ventilation system, air blowers/compressors, a standby generator for emergency power supply, together with electrical panels and control equipment, are housed in a soundproof machinery room (MR). Duplication of essential equipment is preferred in the event of electrical or mechanical failure. Compressed air is required in all phases of culture and carbon dioxide is required for algal culture. In many hatcheries the seawater intake pumps and sand filters are located in a separate pump house close to the point of intake and the final filtration of seawater may take place at the point of use rather than at a central, fine filtration unit.
Since storage is always an issue in a hatchery, it is useful to have a large general-purpose area (GPA) that can be used for storing materials and equipment, packing seed and as a workshop. Most of the working areas should be fitted with benches and sinks (s).
It is preferred that the various parts of the hatchery can be isolated in the event of a disease outbreak.