In other to grow fish, it is necessary to have a suitable fish pond for better fish production. A fish pond is simply an artificial structure/habitat that meets the necessary requirements for growing fish. As you read down, you will learn how fish pond design and construction is carried out from start to finish. Before we discuss the steps involved, let’s look at the general features of a fish pond.
Table of Contents
- Features of a Fish Pond
- Fish Pond Construction
- General Design Considerations
- PROCEDURE FOR BUILDING AN EARTHEN FISH POND
- Materials for Making Screens for the Pond Inlet and Outlet Pipes
Features of a Fish Pond
Although there are many kinds of fish ponds, the following are the main features and structures associated with them in general:
- Inlet/outlet pipes or channels, which carry water into/away from the ponds.
- Pond walls or dykes, which hold in the water
- Water controls, which control the level of water in the pond, the flow of water through the pond, or both
- Tracks and roadways along the pond wall, for easy access to the pond
- harvesting facilities and other equipment for the management of water and fish.
Fish Pond Construction
A typical earthen fish pond should be about 300m2. Although ponds can be much larger than this, having several small ponds rather than one large one will allow you harvest fish more often.
A shortcoming to this is that, many but small ponds are more expensive to construct as compared to a few but larger ponds. Small ponds also waste a lot of space in comparison. However, very large ponds take long to fill and drain and are also difficult to manage.
The physical attributes of a pond usually have a direct influence on achievable levels of production and returns. The main physical factors to consider are the land area, water supply and the soil water retention capacity.
Suitable Land Area for Fish Pond Construction
Select land area with a gentle slope and layout ponds in a way that will take advantage of existing land contours. A farmer should determine an area large enough for the present plans and any future expansion. Also, ensure that such an area is not prone to flooding.
Source of Water Supply for the Pond
A good water source will be relatively free of silt, aquatic insects, potential predators, and toxic substances, and it will have high concentration of dissolved oxygen. The quantity and quality of water should be adequate to support production throughout the culture period.
The most common water sources can be spring water, seepage water, rainwater or run-off, tide water (marine ponds), water from bore holes (wells), or water pumped or diverted from a river, lake, or reservoir. Wells and springs are generally preferred for their consistently high quality water.
Soil Type for Earthen Pond Construction
A simple test can be carried out to determine the suitability of the soil for pond construction:
1. Dampen a handful of soil with water. Use only enough water to dampen the sample (do not saturate it).
2. Squeeze the sample tightly in your hand.
3. Open your hand:
- If the sample keeps its shape, it is good enough for building a pond (sufficient clay present).
- If the sample collapses and does not keep its shape, it is not good enough for building a pond (too much sand present)
The quality of soil influences both productivity and water quality in a pond. Farmers should consider importing clay soil for compacting the pond bottom, sides and core trench to minimize seepage.
General Design Considerations
=> Consider the intended culture practices to be carried out: In designing the fish farm, it should be decided as to where and how many nursery, rearing and stocking ponds are to be constructed.
=> It is important to know the exact size, maximum depth, average depth, and water volume of the pond. This information becomes useful in calculating the amount of herbicide needed for weed control and the number of fish fingerlings needed for stocking.
=> The water source must be able to keep the pond full throughout the culture period.
=> Relatively shallow ponds are productive, but the shallow end should be at least 0.5 m deep to avoid invasion by weeds.
=> It is always desirable to place screens on pond inlets and outlets to keep out predators, insects, and unwanted fish, and to retain the cultured fish.
=> Every pond should be drainable.
=> Every pond should have an independent controlled inlet and outlet.
=> Excavation of a core trench should be done where soils are less suitable.
=> Perimeter and feeder roads are required to provide for movement of machines during construction and at harvest.
=> If you plan to drive on the dykes, build them at least 3 meters wide on top, and wider at the base.
=> Soil used to build dykes should always be compacted in layers.
PROCEDURE FOR BUILDING AN EARTHEN FISH POND
STEP 1: PREPARE THE SITE
- Vegetation should not be included in the soil used to construct the pond dykes, so should be removed from the site prior to beginning to excavate and move soil.
- Remove the topsoil from the site.
- In hilly areas, try to measure the slope of the land with a level or stick to find the best suitable site and orientation for the pond.
- Measure and stake out the length and width of the pond.
STEP 2: PEG OUT THE POND AREA
- After measuring the pond length and width, use pegs to mark out the pond area.
- Decide on the dyke slope and width and determine core trenches pegging.
- The pond dykes should be about 0.5m above the water level (also called ‘freeboard’), to prevent the fish from jumping out.
- It is recommended that pond dykes have a gentle slope of about 2:1. This makes them strong and prevent them from undercutting and collapsing into the pond. However, this ratio depends on the size of the pond. Larger ponds need to have a gentler slope.
STEP 3: CONSTRUCT CLAY CORES
- A clay core is the foundation for the pond dyke which makes it strong and prevents water leaks.
- If you suspect the dyke or pond bottom soil to be highly permeable, dig a core trench, in the same way as you would dig the foundation for a house, under the dykes around the pond.
- Pack the core trenches with impermeable clay and compact it well.
STEP 4: EXCAVATE THE POND AND CONSTRUCT DYKES
- Decide the depth of the pond and begin the digging process.
- Use the excavated soil to build the pond dykes. Do this gradually, and compact each layer of soil added on the dyke before the next layer.
- Try not to use sandy/rocky soil or soil that contain roots, grasses, sticks or leaves. These will decay later and leave a weak spot in the dyke through which water can leak out
- If you have made the pond deep enough, continue digging, but, dispose the soil far from the pond area.
- Once the dyke is constructed, it is better to plant grass on it. The grass roots help to hold the wall together and prevent erosion of the soil.
- If the fish farmer is economically sound, he can go for stone pitched dykes. By using concrete blocks, stones or bricks the earthen dykes will be protected more permanently from crab or rat holes.
STEP 5: INSTALL DRAINAGE SYSTEM
- The essence of the drainage system is to empty the pond when there is a need to change the pond water or harvest fish.
- It consists of the outlet system for letting water out of the pond and the drainage ditches which carry the water away from the pond.
- The best and easiest way to have a good drainage system is to build the pond in a place which provides a good slope.
- The drainage system must be built before the pond dyke because some drainage devices go through the walls.
- One of the easiest ways to drain the pond is to place a bamboo or plastic (PVC) pipe through the base of the wall into the deepest part of the pond.
- An overflow pipe can be installed at an angle into the pond. This should be used only in emergencies. During heavy rains, the overflow pipe takes excess rainwater and runoff water out of the pond.
- The end of the pipe, which is inside the pond, should have a screen over it to keep fish from entering the pipe. The other end of the pipe is plugged with wood or clay or it can be fitted with a tap head. To drain the pond during harvest time, the plug is pulled out.
- Install the intake of the drain pipe underwater. This will prevent the screen from clogging with debris that may be floating on the pond surface.
- The use of pumps and siphon are other methods of draining water from the pond.
STEP 6: INSTALL WATER INLET PIPE
- All ponds, except for those filled directly by a spring or by rainwater, need water inlets.
- During the construction of inlets, filters should be used in the channel so that unwanted fish and other materials do not enter into the pond.
- A water inlet can be as simple as a bamboo/plastic pipe of good diameter running from a water source through the wall into the pond.
- The inlet pipe should be placed about 0.15m above the water level so the incoming water splashes down into the pond. This helps to mix air (thereby introducing oxygen) into the water. It also prevents fish from escaping by swimming into the inlet pipe.
Materials for Making Screens for the Pond Inlet and Outlet Pipes
- If the water is muddy, or has plenty of leaves or grass in it, the wire mesh screen is better.
- Nylon mesh bag will work if the water source is free from organic material.
- If the water contains unwanted fish and more organic matter, sand and gravel filters are best. it is more effective and economical.
- A clay pot with holes punched in it can also be used for screening.
- You can use a loosely woven grass mat as good screen material.
In conclusion, a pond must be able to hold water and sustain favorable conditions for production. One should also be able to undertake the required pond management activities (such as harvesting and feeding) effectively, with relative ease and safety.
Consequently, poorly constructed ponds, give poorer production yields and returns. This is because additional management efforts and associated costs are required to achieve comparable yields. Paying attention to pond design and construction detail is, therefore, the first step to successful pond production.
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