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Tilapia Freshwater Fishpond (Part 1)

The success of freshwater fishpond farming depends on the selection of ideal fishpond site, proper planning and layout design, proper construction and appropriate pond management.

Considering the expenses involved in pond construction, freshwater fishponds smaller than half a hectare are not commercially viable. This technoguide is designed for freshwater fishponds with an area of one-half hectare or more.

Site Selection
Water supply. Water supply is the foremost factor to consider in selecting a fishpond site. The site must be accessible to adequate water supply throughout the year and free from pesticide contamination and pollution. Sources of water can be a surface runoff, stream, creek or irrigation.

Soil characteristics. Clay, clay loam, and sandy loam soils with deposits of organic matter of about 16% are best for fishponds. Hard mud of the above types are preferable to the soft and very loose kind. Avoid sandy, rocky or stony soils because these do not retain water in the ponds. Choose flat terrains for easier excavation and leveling. If the topography is to undulating, the construction costs increase greatly and excavation work removes the fertile portion of the pond bottom. Avoid sites that are frequently flooded.

Other factors to consider are availability of quality fingerlings and cheap skilled labor, accessibility to market and peace and order condition.

Structural Design and Construction of Cages
In designing and planning the layout of freshwater fishponds, give careful consideration to the following:

Pond compartments. There are three compartments in a complete freshwater fishpond system namely: nursery pond, brood pond and production or rearing pond. The nursery and brood ponds may comprise 10% of the total area, and 90% for the production pond.

Water supply. Provide each compartment with an individual water supply system and drainage outlet. Provide also a mechanical emergency spillway for the flow of excess water from ordinary rain and to maintain desired water level in the pond.

Drainage. Construct the pond to facilitate easy drainage when harvesting fish stock and proper cleaning of the pond bottom.

Elevation. Construct the pond one meter or more lower than the source of water supply but slightly higher than the drainage area to obtain at least an average water depth of one meter for maximum production.

Wind direction. Wind plays a role in fishpond design. Strong wind generates wave action that destroys the sides of the dikes. To minimize this, position the longer pond dimensions parallel to the direction of the prevailing wind to lessen the side length of the dike exposed to wave action.

Protection from flood. If the fish pond site is prone to flooding, construct a diversion canal along the perimeter dike to divert runoff water during heavy downpour. Construct a larger and higher perimeter dike to prevent inflow of water.

Designing dikes. Construct dikes with trapezoidal cross section with the top width, the side slopes and the height proportionally designed according to the soil material used. The following are guidelines in designing the dikes:

1. Height above water line. Extend the top of the dike sufficiently above the water line to give a safe margin against overtopping during flood. Include margin for wave action caused by exposure to winds. Perimeter dike should have, after shrinkage, a freeboard height of 0.60 – 1.0 m above the maximum level observed in the locality. Freeboard for secondary dikes is 50 cm.

The allowance for settlement and shrinkage depends on the characteristics of soil fill, soil foundation, and on the method of construction. On the average, an allowance for settlement and shrinkage is 25%. Provide a settlement allowance of not less than 40% for soils high in organic matter while dikes compacted by construction equipment is 5% less than the filled height.

2. Top width. The minimum top width or crown is 1 m for dikes less than 3 m high. The top width of dikes used as access road is 4 m. Provide a 0.60 m wide berm or shoulder on each side of a roadway dike to prevent rovelling.

3. Side Slope. The side slope or steepness of the dike is the ratio of the horizontal length to the vertical rise. Fishpond dikes lower than 3 m should have a slope of 1:1. Dikes above 3 m should adopt a 2:1 slope. Refer to the table below for relationship among the top width, bottom width and height of dikes.

Relationship among the top width, bottom width and height of dikes with a given side slope.

Height
Top width of crown (m)
Bottom, with in m. at given side slope
1:1 ratio
1.5:1 ratio
2:1 ratio
1.5
1
4
5
7
2
1
5
7
9
3
2
8
11
14
4
3
11
15
19

Construction of Pond System
Plan fishpond construction carefully and systematically. The system of pond construction is based on the prepared program and schedule of development.

Dike construction. Clear the dike site of vegetation, slumps and debris. Clear the strip 2-4 m wider than the base of the dike. For sites with decaying matters, construct a puddle trench at the center of the path of the dike. Excavate 0.5 m wide by 0.5 m deep trench filled with clay soil to prevent excessive seepage on the finished dike. Dig blocks of mud for construction of dike at least one meter from its base. Allow each layer to settle firmly before adding another layer until the desired height is attained. Construct dikes either manually, mechanically or both.

It is very important to have a uniform dike height. To do this, get a 50 m long transparent plastic hose. Fill the hose with water. Hold one end of the hose at the first station and the other end at the next 40 m away. If the water level at both ends are the same, the dike is level. Repeat the process until the last station has been marked.

Canal construction. Construct the canals simultaneously as the adjacent dikes. Stake markers to serve as guide during the excavation of canals. Slope the canal gently towards the drainage gate of pipe to keep the flow of water sluggish and to avoid excessive erosion.

Construction and Installation of Water Control Structures. Water inlet or outlet structures are usually made of wood or concrete gates, galvanized iron sheets or reinforced concrete pipes.

Place 3 pairs of grooves on each side of wooden or concrete gates extending to the top of the dike where they are installed. The middle pair of grooves allows the removable slabs to regulate the flow of water. The first and third pairs enable the screens to prevent the escape of cultured fish. These screens may either be of bamboo splits or nylon attached to a wooden frame.

In freshwater fishponds, galvanized iron pipes or reinforced concrete pipes are often used instead of concrete wooden gates. The following is a guide in determining the proper pipe diameter to be installed.

Size of drain pipe in inches – Condition
• 4 – Can drain 1 ha. pond with average depth of 1 m in 6 days
• 6 – Can drain the same in three days
• 12 – Can drain the same in one day

With proper scheduling of draining time, it is adequate to use 4 to 6 inch pipe for one hectare pond and 6 to 11 inch pipe for larger ponds. Construct water supply and drainage system simultaneously with the dikes.

Pond Bottom Leveling. Mechanical leveling is cheaper and faster than manual leveling if the pond bottom can support the equipment used. Use farm tractors or tillers with a back blade. The carabao and the harrow may be used in small ponds. The pond bottom should slope gently towards the drainage gate to facilitate complete drainage.

After leveling the pond, plant creeping grasses at the dikes to prevent erosion. Plant bananas at the outside slope of the perimeter dike to serve as wind breakers. Do not plant trees along the dikes because the roots will cause leakage and seepage.