I. Essentials in site selection
(a) Studies of watershed and flooding records. This is to determine the possible future effect of fishpond development and to take appropriate precautions.
(b) Tidal studies in the locality. The local tidal characteristics regarding highest tides, lowest tides, annual absolute range and normal daily fluctuations are important considerations. For final determination of the suitability of a specific site, its elevation based on 0 tidal datum is important (See also ANNEX 11.
(c) Area available and topographic survey - Area and topographic survey are essential in planning layout and construction specifications.
(d) Water supply and quality. This is related to (b) above but more thorough survey has to be conducted once a site has been chosen for development. Salinity, turbidity, exposure to pollution and pH should also be considered.
(e) Soil properties. For fishpond purposes the characteristics to be emphasized are: (i) load bearing capacity, (ii) pH, (iii) quality at different horizons, down to at least one meter (soil drill to be used), (iv) content of organic matter, etc.
(f) Climatic conditions. These include rainfall, temperatures, prevalent winds, rate of evaporation, seasons specially with regards to number of sunny days per year, etc.
(g) Vegetation. The type can be good index of site elevation, type of soil, etc. The expense for development will depend on age and size of trees. Buffer zones ranging from 10 to 50 meters from river banks or exposed coastal shores are advisable for wind and wave brakes. Some vegetated areas within big pond systems may be required.
(h) Availability of management and labour manpower. This can be developed in time in fishpond development centres. Proper training of these industry manpower can contribute to the future of the industry.
(i) Marketing problems. These will include: (i) ice plants (ii) cold storage plants (iii) boats, trucks and rates of charges (iv) prevailing prices of products (v) availability and prices of input supplies.
(j) Accessibility and infrastructure. These should consider roads, harbours, airports and structures for educational health and social institutions for fishpond communities.
(k) Layout. This will depend on area available, topography, species intended to be cultured and type of management procedure to be adopted.
(l) Construction. The procedure to be adopted will be based on the characteristics of the site as a whole.
(m) Selection data evaluation. Since the factors to be considered in selection of sites for development and in determining the suitability of each particular site are many, proper selection and determination should be based on the combined effects of the various factors considering the relative (weighted) importance of these factors. The exercise done during the survey of prospective sites in West Malaysia is an example (ANNEX 7.)
Secondary gates (Figures 10a and 10b) are usually now located not centrally but toward one end of the narrower side of the compartment. This gives good water turbulence and circulation during the water filling and discharging operations.
The less gates there are, the less is the initial cost and also the maintenance. There are no gates between rearing compartments. For Chanos culture, only one canal is used for both supply and discharge while in shrimp culture there are separate channels for supply and discharge hence two gates per rearing compartment.
Diversion canals are constructed where there is much water runoff from adjoining field. This prevents sudden salinity changes, entry of polluted water that is loaded with pesticides and also prevents entry of silted water into the pond complex.
Pond compartments for Chanos nurseries usually constitute from 1 to 4 percent of the total area. The more entensive the culture, the wider are the nurseries. If the pond complex is geared to hit the low income bracket market and harvest of fish is of about 250 gm/piece, then the nurseries and transition ponds may be increased by 2-3 or more percent of the total area. Bottom elevation of nurseries are usually same or slightly higher than rearing ponds. Location of nurseries are usually away from perimeter dikes but as close to the water supply gates as possible. It is now a common practice to have roofed small acclimatization compartments at the corner of the nursery or fry pond.
Transition ponds also occupy like the nurseries from 1 to 4 percent or may be a bit larger. Bottom elevations may be lower than rearing ponds. The location is usually near the nurseries.
In the past, 20 to 50 ha compartments were not uncommon. However, with new intensive methods, most of the rearing ponds are limited to a maximum of 5 or so hectares. This gives the operator better pond water and stock control. The tendency seems to be toward smaller units for flexibility and better marketing strategies. Elevation of rearing pond bottom for milkfish usually are such that only maximum of 40 cm of water can be held in the ponds during culture periods. In modern ponds, a canal system to completely drain the water in the rearing ponds is usually built. This facilitates quick draining and complete and immediate drying.
In principle, the good ponds are those with individual water control for each pond. Some intensively managed ponds are now yielding close to 3 tons/ha/year.
II. Water control structures
Water control structures consist of gates, culverts or pipes. The main gates regulate the exchange of water between the pond system and the tidal stream or sea. This may be made of reinforced concrete, or of wood. Reinforced concrete is comparatively more expensive but once constructed it usually outlasts the existence of fishpond. Such a gate have one-or multiple (2-, 3-, 4-, etc.) opening depending on relative size of the fishpond unit to be served. The details of structure of this type of gate is shown in this report (Figure 10 a).
The construction and installation of a wooden main gate is shown in ANNEX 6, Figures 6c and d.
A recent innovation for smaller and less expensive main or secondary water control structure makes use of culvert. This is usually made of concrete howlow blocks. The details of construction of this type of gate are described (Figures 10 b and c).
Secondary gates are usually made of wood. A pattern for this water control structure is illustrated (Figure 10 d). For smaller ponds such as the nursery or fry ponds and transition pond pipes are often used.
III. Layout
The layout of the pond system will depend on the size and shape of the area. These will also determine the number and sizes of ponds and position of water canals and gates.
FIGURE 10 a
MAIN WATER
CONTROL GATE
OF REINFORCED CONCRETE
FIGURE 10 b
USE OF CULVERT PIPES AS
SECONDARY GATES
FIGURE 10 c
CUT - OUT DIAGRAM OF CULVERT PIPE
CONSTRUCTION AS SECONDARY GATE
FIGURE 10 d
SECONDARY WOODEN GATE
