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| Source: @catfishfarminginnigeria |
Designing and building fish pond is determined by some factors like fish pond site, type of fish culture to be adopted, size of fish farm, brood stock and quantity. It is important to carry out feasibility study and select the appropriate site fish pond construction.
Types Fish Pond
There are different fish culture facilities. Depending on the facilities designed to serve as enclosures in rearing, fish can be grown in various facilities. These facilities increase the opportunities available for aquaculture practices either in the field (fish farm) or at home. The types of fish ponds and how to construct them are discussed below:
1. Earthen Pond
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| Source: @catfishfarminginnigeria |
Steps in building earthen fish pond
i. Prepare the site
First clear the bush, cut down trees, remove rocks in the site you want construct the pond. Measure and peg out the perimeter of the pond. Remove the top layer of the soil containing roots, leaves and others, deposit this outside the pond area. Save the topsoil for later use when grass is to be planted on the pond dikes.
ii. Build a clay core
A clay core is the foundation for the pond dike, which makes it strong and prevents water leaks. A clay core is needed in contour ponds and is built under those parts of the dike which the water will be above the original ground level. A clay core is not needed in excavated ponds because there the water level is below the original ground level.
Remove all the topsoil in the area of the pond dikes and dig a core trench in the same way as you would dig the foundation of a house. The trench needs to be dug out along the lower side of the pond and halfway along each short side of the pond. Fill the trench with good clay. Add layers of clay at a time (20-50cm) and then compact it well. This will provide a strong foundation upon which the pond dikes can be built. The core trench helps to strengthen the pond dike and keeps it from leaking. There is a tendency for water to seep away where the new soil joins the original ground layer. Where there is no clay core and water seeps out under a new dike, this leakage may eventually cause the entire dike to break down. Where there is a clay core, the clay stops the water from seeping under the newly built dike.
iii. Dig the pond and build the dike
Use the soil that you dug out when making the trench for the clay core to build up the dike on top of the core trench. Try not to use sandy or rocky soil or soil containing any roots, grass, sticks or leaves. These will decay later and leave a weak spot in the dike through which the water can leak out.
Compact the soil at regular intervals while you are building the dike. After adding each 30cm of loose soil trample it well while spraying water on the dike. Then, pound it with a heavy log, or a piece of wood attached to the end of a pole. This will make it strong.
Pond dikes should be about 30cm higher than the water level in the pond. If catfish are to be farmed in the pond, build the dike to 50cm higher than the water level to prevent the catfish from jumping out. Once you have reached this height, add a little more soil to allow for settling and then refrain from adding any more soil on top of the dikes. If you have not yet made the pond deep enough, continue digging, but take soil away from the pond area. If you put the soil on top of the pond dikes, they will become too high and unstable, and it will make working around the pond difficult.
The pond dikes should have a gentle slope, which will make them strong and prevent them from undercutting and collapsing into the pond. The easiest way to slope the dikes is after digging out the main part of the pond. The best slope for the pond dike is one that rises 1m in he I for every 2m in length. A good way to determine whether the dikes are too deep is to try to walk slowly from the top of the dike to the pond bottom. If this is not possible, then the dike is too steep. The pond bottom should also slope so that the water varies in depth along its length. Smooth out the pond bottom after reaching the required pond depth, this will make it easy for sliding the nets along the pond bottom when harvesting the fish.
iv. Build the water inlet and outlet
The water inlet consists of a canal to bring in the water, a silt catchment basin, and a pipe to carry water into the pond. The water coming into the pond often contains a lot of soil and silt and will make the blond very muddy. A slit catchment basin will prevent this soil from entering the pond. By widening and deepening the inlet canal right outside of the pond dike, the soil will settle into this silt catchment basin after which it is allowed into the pond through the inlet pipe. It should be about 15cm above the level so that the incoming water splashing down into the pond. This will prevent fish from escaping by swimming into the inlet pipe. It also helps to aerate the water.
The water overflow pipes is used only in emergencies. Water should not flow out of the ponds on a daily basis. During heavy rains the overflow pipe takes excess rainwater and run-off water out of the pond. The inlet, outlet and overflow pipes can be made of metal, plastic, bamboo, wood or other materials. Install the pipes though the pond dyke near the water surface. Pipes should have screens to stop fish from entering or leaving the pond.
v. Protect the pond dikes
When the pond dikes are finished, cover them with the topsoil that was saved when digging the pond. On the dikes , plant grasses such as star grass (Cynodondactylon). Do not use plants with long roots or trees because these will weaken the dikes and may cause leaks. The fertile topsoil will help the new grass to grow, and the grass will help to protect the dikes from erosion. Flooding during heavy rains can destroy pond dikes, I’d too much rainwater and run-off water flows directly into the pond. This problem is most common in contour ponds built on hillsides, but can prevent by diverting the run-off water around the sides of a he pond. This can be done by digging a ditch along the upper side of the pond.
vi. Fence the pond
Put a fence around the pond that will protect pond from thieves and predatory animals like crocodiles, snakes, frogs etc, and prevent children from falling into the pond. To make a low cost and sturdy fence, thick hedges can be planted around the edge of the pond or the fence can be built using poles and thorn branches.
vii. Fill the pond with water
Before filling the pond, put rocks on the bottom of the pond at the spot where the water lands when coming in from the inlet pipe. This will keep the incoming water from making a hole and eroding the pond bottom. Then open the inlet canal and fill the pond. Fill the pond slowly so that the dikes do not subside due to uneven wetting. While the pond is filling, the water depth can be measured with a stick. Stop filling the pond when the required depth is reached.
To prevent overflow, ponds should not be filled to the brim, a free board should be left. Water in the pond should not flow too frequently because water flowing through the pond will flow down fish growth by flushing away the natural fish food. This is especially important where large ponds are used and feeding frequently is low. The only water added to the pond should be to compensate for water loss through evaporation and seepage. New ponds often seep when they are filled with water for the first time as the soil partly takes up the water and some percolate. Therefore, continuous of water addition of water for several weeks will enhance water holding capacity of the pond.
2 Concrete Pond
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| Source: @catfishfarminginnigeria |
This is the most convenient to construct, but it is relatively permanent and immovable structure once constructed. Concrete ponds are suitable in living premises, more secure and convenient to manage. However, they are only. But once a good concrete structure has been built, it can last for 10-15years with minimal maintenance. Concrete ponds are preferable in areas where the soil is too sandy for earthen ponds or enough land is not available or then pond is required within the living premises. Cost of construction of concrete pond vary with the size of pond, location, availability and cost of labour, source of water and cost of materials such as cement, sand, gravel, plastic pipes, solid blocks, etc.
Steps in building concrete ponds
i. Site selection
Select a suitable site that can be used for the concrete/ cement block structure. This can be within a living premises or a separate location. Ensure also that a regular water source is guaranteed.
ii. Design the pond
Decide on the size of the pond to be built. Concrete ponds should not be too large because of the volume of water it will hold. It is better for a farmer to have for example, units of 4m x 5m x 1m concrete ponds than a single 10m x 10m x 1m pond. The bigger a concrete pond is the more the risk of structure failure and higher maintenance cost. Pond unit economic size for a first timer can be 12m³ to 25m³.
iii. Construction of the pond
The services of experienced builders familiar with pond structure should be deployed. Dig foundation depth to accommodate 18inches block height and lay it properly. Spread waterproof nylon before flooding and ensure good proportion of sand and cement. Raise the pond walls to between 0.8m-1.2m high. Good mixture of gravel, sand and cement must be used and the blocks holes properly filled. Good finishing in plastering must be ensured. All inlet and outlet structures must be properly constructed. Fill the structure with water for at least one week to test its water retention capacity and wash off cement remnants before stocking with fish.
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