In nature, many fish never reach adult size because they are eaten by other animals or predators or die from disease or lack of oxygen. Fish culture in ponds try to control the situation in order to produce more fish. In ponds, predators can be controlled so that the pond yields more fish than the natural waters. Growth of fish in ponds is mainly due to the fact that fish cannot escape, and feeding, breeding, growing and harvesting the fish is carried out in a well-planned way.
Fish culture is practised in ponds. These are small shallow bodies of water in natural conditions and completely drainable, usually constructed artificially. The natural ponds differ from the lakes in having a relatively large littoral zone and a small profundal zone. Their source of water may also vary.
Site selection
One of the most important aspects of the planning of fish farms is the selection of the site for the fish ponds. If the site of the ponds is well chosen, the pond can be more productive than the land itself. When considering a site for the fish ponds, several aspects have to be considered like the type and number of ponds to be constructed, the topography of the area, the water supply and the type of fishes to be reared.
Poor agricultural land can be converted into very good fish farms. If the soil is good the fish production will be high. If a pond is constructed on agricultural land which is not producing good crops, and the pond is managed correctly, eventually the pond bottom soil will become more fertile than it was earlier. After harvesting, the pond can be planted again with a land crop like corn and allowed to grow. When the corn is harvested, the land can be turned back into a fish pond. This means that the land can be used for 2 economically viable crops (one fish crop and the other corn crop) instead of one poor crop. Fish can be cultured along with paddy in the paddy fields. This means that the land is used for both the purposes, and in such cases, the choice of how the land should be used is very important. Only fishes can be reared in the ponds throughout the year.
Criteria for site selection:
1. Availability of land in a continuous, suitably shaped plot of optimum size with all facilities.
2. The site should have assured water supply of adequate quality either surface or ground water.
3. Soil and water of the site must be suitable for fish culture.
4. The site should be free from floods.
5. The site should have good transport facilities and approach roads.
6. The site should have electrical and telephone connections.
7. The fish seed should be available easily and in plenty in that area.
8. Marketing facilities should be available near the site.
9. The site should be away from populated areas.
10. The site should be connected to a drainage system.
11. The site should be away from polluted areas.
12. The fishermen or labour should be available near the site.
The following are the major factors that work together to make a good site for a fish pond.
Water supply:
Water supply is the most important factor in selecting a site. Fish depend upon water for all their needs. If a site has water available all the year-round, that site passes its first test easily. If water is not available all the time but there is some way to store water for use when the natural water supply is low, then that site may still be considered. The most important factor is that water must be available at all times and in good supply. A dependable source of water supply must be available near the site. There should be adequate water to fill the ponds and maintain water level which does not fluctuate more than 50 cm. Common water sources for carp culture ponds are rivers, streams, springs, canals and surface runoff from rainfall. Water from any of these sources would be suitable for fish culture, provided it is free from contamination. The natural sources of water are;
1. Natural water : Most ponds are filled with water that comes from natural springs or that has been diverted and brought in from rivers, streams, or lakes.
2. Springs : Some ponds are built where there is a spring to supply the water. Spring water is obtained from underground, and is a very good source for fish culture because it is uncontaminated, without undesirable fishes and fish eggs. If the water from a spring has travelled very far, it may need to be filtered before it is used for a fish pond.
3. Rainfall : Some ponds called “sky ponds”, rely only on rainfall to fulfil their need for water.
4. Run-off : Some ponds are gravel and sand pits which fill when water from the surrounding land area runs into them.
5. Wells : The best source of water for a fish pond is well water. Continuous water supply can be obtained from wells. Well and spring waters are often low in oxygen content, and fish need more oxygen in the water. The oxygen can be added to the water by agitating the water in the pond, stirring the water in the pond, by beating the water with bamboo sticks, and by running small motors in the pond.
In most of the cases, water from the rivers, streams or lakes is used for filling the fish pond. A diversion canal is dug between the water source and the pond to take water from the source to the ponds. It is a good way to fill a pond because the water can be controlled easily. When the pond is full, the channel can be blocked with a gate or a plug and water will stop moving into the pond.
There are a few problems with this type of water supply. In the tropical areas, streams flood during the rainy season. This extra water can be dangerous to the pond, and should be sent out through a channel. When a pond floods, all the fish escape and the pond is empty. This water should be filtered, otherwise, unwanted fishes and their eggs enter into the pond. If the water is very clear, which is from the water source, it may have to fertilize the pond because there are not enough nutrients. If the water is muddy, it will have to settle before it is used in the pond. A separate place will have to be made where the mud can settle out of the water before this water enters the pond. If the water is bright green in colour, it has a lot of fish food organisms. If the water is dark, it may have acid in it, and lime has to be added to the water.
Soil:
The other important aspect of the site selection is the soil of the area. The soil of the pond must be able to hold water. It also contributes to the fertility of the water due to its nutrients.
The best soil for a pond is one that contains a lot of clay. Clay soils hold water well. If the soil feels smooth and slippery, it probably means there is a lot of clay in it. If it feels gritty or rough to touch, it probably contains a lot of sand. The smooth soil is good for a fish pond. If the clay is more in the soil, its water retention capacity is more, and it is better for building a pond.
A good way to ascertain whether the soil is right for a fish pond, is to wet a handful of soil with just enough water to make it damp and then squeeze it. If it holds its shape when the hand is opened, it is considered to be good for a pond.
In sandy soils also ponds can be constructed, but more efforts are required which sometimes may not be successful. Large ponds can be constructed in clay soils only. If the soil is rocky or of shifting sand, only small ponds are possible. Soil also contributes to the pond’s fertility. Fertility is a measure of the nutrients in the pond and it simply refers to how much food is available in the pond for the fish. Usually fertile ponds contain large amounts of fish food organism. The soil of the pond contains necessary nutrients like Fe, Ca and Mg. In addition, soil also consists of acid which is harmful to fish. Sometimes after a heavy rainfall, high fish kill is observed in new ponds. It is due to the heavy rains carrying large amounts of acids from the soil into the ponds.
A good indicator of the quality of soil is whether it has been used for growing crops. If crops grow well in that location, the soil will be good for the fish ponds.
Porous and peaty soil must be avoided as this will neither retain water nor permit compaction. There will be excessive seepage of the soil if it is of organic nature and porous. The subsoil must be checked by taking random samples from the area in order to ascertain whether or not there is 1-1.5 m layer of clay under the pond bottom.
Topography
The third important factor in site selection is topography. It is used to describe the shape of the land, whether it is flat or hilly, upland or lowland etc. The topography of the land determines the types of ponds which can be constructed. The location, shape and size of the pond are determined by the topography of the land and by the farmer’s requirements. The most useful topography for fish ponds is that which allows water to fill the ponds and drain them by using gravity. Ponds built on a slope, can be drained easily. If the ponds are located on flat land, the pond must be built with a slope inside it so that it can be drained by gravity or it will have to be drained using a pump.
The ponds should generally be flat or gently sloping towards the outlets. Topography guides the cost of construction and intake and outlet of water for every pond. The site should be so selected that the earth available by excavation should, as far as possible, balance with the earth required in filling or raising dykes. Prior to designing and construction, the site should be thoroughly surveyed to determine the topography and land configuration.
The number, shape and size of ponds
The number of ponds depends on the possible site (Fig. 4.1 and 4.2). The site should have a place for nursery, rearing and stocking ponds. The size of the ponds depend on the topography, water supply and need. Nursery ponds are smaller than the rearing pond, because the fry are very small. Rearing ponds are usually bigger than nursery ponds and stocking ponds are the largest ponds in the fish farm.
The smaller ponds have the advantages like easy and quick harvest, quick drain and refill, easy treatment for diseases and are not eroded by wind easily. The advantages of the larger ponds are that it costs less to build the ponds, these ponds take up less space per hectare of water, have more oxygen in the water and can be rotated with rice or other crops.
More smaller ponds are better than few larger ponds in the fish farm as the larger ponds are difficult to manage. The width of the ponds should not exceed 40 m, so that relatively lesser and limited number of fishermen would be sufficient to harvest the fish. If the ponds are rectangular, the operations will be easier.
The depth of the ponds depends upon the fish being grown. Fish species like different kinds of food, and the depth of the ponds affects the kinds of food produced by the pond. A common carp, for instance, eats worms and other bottom organisms and must have a pond that is
not deeper than 2 m. But when the carp are in the fry stage, they eat only plankton and the tiny floating plants and animals suspended throughout the water. So nursery ponds for carp fry are often only 0.5 m deep. A deeper pond will not produce much food because the sunlight cannot enter into deeper parts of the ponds. A very shallow pond might become turbid, covered by water plants easily and also become very hot.
Square shaped ponds are economical to construct with minimum length of dyke. The width of the pond should not exceed 40 m for facilitating the netting operations, and hence a rectangular pond is preferable.
The slopes of the ponds and bundhs (Fig. 4.3) may vary from 1 ½ horizontal : 1 vertical to 2 horizontal : 1 vertical. The bottom of the pond should have a slope towards the outlet. Ponds should have controlled inlets and outlets, so that these can be drained and filled easily. The deeper ponds should be placed on the lower contours, so that lesser earth work is involved.
Survey
The first step in the construction of a fish pond is marking of the area of the proposed pond. The natural slope where the main wall is to be built should be ascertained. The main wall should be marked off at the lower end of the pond, where the slope is the greatest. This is where the drainage system of the pond will be laid. Even flat grounds have some kind of shape, although it may be very little. Before constructing, the land is surveyed to find out as to which side of the land has the slope.
Designing
While designing the fish ponds the first step should be to study the survey reports and maps, soil type, topography and water supply etc. The entire design and layout of ponds and dykes will follow according to the survey reports. In designing the fish farm, it should be decided as to where and how many nursery, rearing and stocking ponds are to be constructed.
In case of a fish farm constructed solely for the purpose of seed production, only nursery and rearing ponds may be constructed, with a nominal area for the stocking pond reserved for stocking the breeders.
In case of a fish production farm, more stocking ponds will be constructed to produce Table size fish after stocking fingerlings. For a composite fish farm all three types of ponds are required and their number should be based on the intended stocking density.
Construction
After the designing, it is necessary to prepare the detailed estimates of the items of work to be carried out as per the design. The approximate cost of construction is also to be estimated.
Construction time:
The construction time of the pond is an important factor for pond management. If the construction of the ponds is completed in summer, the pond can be used for cultivation immediately.
Preparation the site:
The site should be cleared before the construction. All the bushes and small plants, etc. should be cut and removed along with their roots. The roots should be totally removed, otherwise the leakage problem will arise later on. If there are any trees near the construction site, it is better to cut the branches towards the site, so that the sunlight is not blocked and the leaves do not fall in the water. It is better to have trees near the ponds, but only 5m away from the pond.
Mark out the ponds:
When the pond area is cleaned, it is necessary to mark the outlines of ponds and dykes. Mark out the main wall or dyke and other walls with stakes. The walls should be wide. Plan the depth of the pond and height of walls. The walls should always be at least 30 cm higher than the water level for a small pond, and at least 50 cm higher for a larger pond.
Excavation of the pond:
The excavation can be carried out either by manual labour or by bulldozers. If the bulldozer is used, final shaping should be given by manual labour. The sides and bottom of ponds should be properly finished and trimmed until a good slope for drainage is made. The pond bottom should usually have a slope of 2-5%. If the land for the pond is chosen well with regard to the natural topography, only a small part of the pond bottom will need to be dug out. The most important feature is to have the pond bottom slope such that the pond can be drained. If the pond site has a natural slope, the dyke or main wall should be constructed at the low level side. When the pond walls are constructed, the excavated soil can be placed on the top and planted with grass. This fertile top soil will root grass easily and this will help keep the walls from eroding.
The pond bottom must be cleared by removing small rocks, roots,
and stumps, so that the nets, during harvesting, will not get caught and torn. If grass is found in the pond bottom, it need not be removed, because after filling up the pond with water the grass will die and rot and add nutrients to the water.
When the stakes have been established for construction of dykes, about 2′ top soil should be removed as it consists of large amounts of roots and other organic material. The core trench is cut immediately after the removal of the top soil. If the soil is porous, the seepage problem may arise at a later stage. It would be essential to provide a clay core in order to prevent seepage. A soil which is a mixture of sand and clay is best. Pure clay soil will give cracks and leak. If pure clay is to be used, it must be mixed with other soil before it can be used. Turf, humus or peaty soils should not be used. All stones, wood pieces and other material which may rot or weaken the wall must be removed before building begins.
The construction of the earthen dyke (fig.4.4) is always economical. The soil which is obtained from digging can be used to prepare the earthen dyke. The filling of earth should be done in layers not exceeding 20 cm in height and consolidate each layer by watering and ramming. The earth work for the dykes should be thoroughly compacted so that even minor seepage can be checked. If the fish farmer is economically sound, he can go for cemented dykes.
The dykes of a pond should be strong enough to withstand weather action. In big ponds erosion of dykes is a problem which requires regular attention. Brick and stone pitching may be provided to arrest erosion of dykes. The earthen dykes can be protected from erosions with bamboo piling with bamboo jabfree on the top. The holes, which is another common problem, should be closed immediately with stiff clay mixed with lime and cementing material and should be compacted properly. By using concrete blocks, stones or bricks the earthen dykes will be protected more permanently from crab or rat holes.
Side slopes of embankments depend upon the nature of material used for construction. The slopes should be flatter than the angle. Soil with a lot of clay in it can have a greater slope on the outside wall than on the inside wall. A typical embankment is built with an outside slope of 1:1 and an inside slope of 1:2. A slope of 1:2 means that for every change in length of 2 m there is a change of 1m in length.
Once the embankment 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. Trees should not be planted on the wall, as the tree roots grow they will crack and destroy the wall.
Drainage system:
A drainage system is used to empty the pond. 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 embankment because some drainage devices go through the walls. One of the easiest ways to drain the pond is to place a bamboo or plastic pipe through the base of the wall into the middle 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. To drain the pond during harvest time, the plug is pulled out. Other methods of draining the ponds are the siphon and the pump, which are not used as often. In the siphoning system, a rubber or plastic tube is fixed with one end inside the pond and the other end outside the pond, but this tube must be lower than the inlet. A vacuum is produced in the pipe to dewater the pond. Pumps can be run by engines to help drain the ponds, but it is a costly exercise.
Sluice:
The sluice can be a screened gate in a water channel going into the pond or a drainage gate leading water out of the pond.
In a pond drainage sluice gate is anchored into the main wall or dyke by extending the sides of the sluice into the wall so that the sluice
structure stands upright and it is in the centre. The sluice can be made of wood, cement and brick. It can be made up of one or two wooden gates which are removed to empty or fill the pond. A sluice also has a screen gate to keep unwanted fish from entering at the inlet and pond fish from leaving at the outlet.
The monk (Fig. 4.4) is much like the sluice, but it is not built into the pond wall, the way a sluice is. A monk is never used at the inlet as a sluice can be. The monk type drainage system controls the level of the water and prevents fish from escaping from the pond.
Water inlet
All the 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 the unwanted fish or other material do not enter into the pond and the water is clean. A water inlet can be as simple as a bamboo pipe of good diameter running from a water source through the wall into the pond. The inlet pipe should be placed above the water level.
A wire screen makes a good filter. The horizontal screen is very effective. Here the screen is placed so that the water passes through as it falls into the pond. The screen merely juts out from the wall at the inlet. The vertical screens can also be used. A nylon mesh bag makes a good filter and can be fixed to the inlet pipe. A sand and gravel filter is also used, but it requires a small tank at the water inlet, more effective and economical. A saram fibre filter is basically like a wire screen that is placed horizontally underneath the water inlet, but these must be cleaned often and are costly.
After examining the water source, selection of the filter is done. If the water is muddy, or has plenty of leaves or grass in it, the wire screen is better. If the water source is free from organic material, the mesh bag will work. If the water contains unwanted fish and more organic matter, the saram filter and sand and gravel filters are best. To clean the filters, it should be removed and cleaned with a brush and fresh water, or, the filter may be flushed with water against the water flow. This is known as backwashing. These filters should be cleaned each time when water is let into the pond.
Sealing the pond bottom:
The last step in pond construction is sealing the pond bottom so that it does not leak. If the soil has more clay in it, no special sealing is needed. If the bottom is sandy, it should be sealed to hold the water. To seal the bottom a clay core lining is built over the pond bottom. Another method of sealing the pond bottom is with cement blocks, but it is expensive. Sealing with polyethylene, or plastic or rubber sheet liner is another method of sealing. Yet another technique developed in the USSR, is called gley or biological plastic. In this method, the pond bottom is covered with animal manure after cleaning the bottom. The animal manure layer is then covered with banana leaves, cut grasses or any vegetable matter, and a layer of soil is put on it. The layers are rammed down very well and 2-3 weeks are allowed to elapse before filling the pond.
Summary
Growth of fish in ponds is mainly due to the fact that fish cannot escape, and feeding, breeding, growing and harvesting the fish is carried out in a well-planned way.
Fish culture is practised in ponds. These are small shallow bodies of water in natural conditions and completely drainable, usually constructed artificially.
One of the most important aspects of the planning of fish farms is the selection of the site for the fish ponds.
Fish depend upon water for all their needs.
The soil of the pond must be able to hold water. It also contributes to the fertility of the water due to its nutrients.
The first step in the construction of a fish pond is marking of the area of the proposed pond.
While designing the fish ponds the first step should be to study the survey reports and maps, soil type, topography and water supply etc. The entire design and layout of ponds and dykes will follow according to the survey reports. In designing the fish farm, it should be decided as to where and how many nursery, rearing and stocking ponds are to be constructed.
If the construction of the ponds is completed in summer, the pond can be used for cultivation immediately.
The dykes of a pond should be strong enough to withstand weather action.
A drainage system is used to empty the pond. 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 sluice can be a screened gate in a water channel going into the pond or a drainage gate leading water out of the pond.
Source: Aquaculture