BREAKING NEWS

ARTIFICIAL PRODUCTION IN AFRICAN CATFISH


ARTIFICIAL REPRODUCTION

5.2.1           GONADAL DEVELOPMENT IN CAPTIVITY

          The female Africa catfish has a fully development ovary which contains “ripe” eggs the whole year through, if kept in ponds and once the water temperature remains above 220c. The eggs of a “ripe” female make up 15-20% of the body weight (i.e. a “ripe” female of 1 kg having about 150-200 gram of “ripe” eggs). The oocyte development decreases once the temperature drops below 220c and we see that the ovary makes up approximately 5% of the body weight of the female. Artificial reproduction is still possible but the number of eggs obtained is small and the quality of the eggs decrease as can be seen from the decrease hatching percentage.

NATURAL PRODUCTION IN AFRICAN CATFISH.


NATURAL REPRODUCTION

          C. gariepinus shows a seasonal gonadal maturation which is usually associated with the rainy season. Research carried out by Graaf and his team in 1995 shows that maturation processes of C. gariepinus are influenced by annual changes in water temperature and photoperiodicity and the final triggering of spawning is caused by a rise in water level due to rainfall. An instance of maturation and spawning of C. gariepinus in Lake Victoria (Kenyua) is presented in Figure 5.1; reproduction starting in March just after the start of the first heavy rains as is indicated by the decrease in the Gonad. Somatic Index1 (G.S.I.) Natural reproduction is completed in July and the G.S.I. remains low till November, thereafter the oocytes start maturing gradually and become ripe again in March. 

FERTILIZATION IN FISH FARMING


FERTILIZATION

The most critical factor for the successful nursing of African catfish larvae is the ready availability of zooplankton during the first week after stocking, as they feed only on live food during this period (de Graaf et al., 1995). A good zooplankton bloom can only be obtained if the ponds are well fertilized.

LIMING IN EARTHEN POND


LIMING

Liming is an important part of nursery pond maintenance; having a fovourable effect on the health of the fry and increasing the natural productivity of the ponds. Some of the beneficial effects of liming can be summarized as follows:

Ø Disinfection of the pond bottom (only quick lime).

Ø Increase the pH of water and pond bottom to an optimum level (pH 7-9) for plankton and fish production.

FRY NURSING IN EARTHEN PONDS


FRY NURSING IN EARTHEN PONDS

Four factors are of grate importance when nursing first feeding larvae within in earthen ponds;

Ø The availability of large quantities of zooplankton

Ø He stocking density of the 3 day old larvae

Ø The duration of the rearing period

Ø The pond size or the ratio dike length and pond surface

LARGE SCALE FISH FARMING USING MOBILE TARPULIN POND

The easy way of having a mega fish farming without spending much money on pond construction and having a lasting pond that grows fish faster is by using the tarpaulin pond.
it is cheap and can last more than the concrete pond.



 
 
 
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HOW TO MAINTAN WATER LEVEL IN THE POND


FILLING THE POND

Fill the pond with water after properly screening the inlet and stock it within 7 to 10 days of filling. However, ALWAYS check that the water quality is suitable for fish production before stocking, especially if treatments have been applied to the pond. If no water quality test kit is available, place a few catfish in some netting material for a couple of days before the intended stock date. If the fish do not die, then most probably the pond water quality is good enough. The pond can then be stocked. If the fish die, wait for a couple of days and try again. Stocking the pond as soon as possible after it has been filled, gives the stocked fish a head start before other animals, such as frogs and predatory insects establish themselves. Frogs can tell when fish are in a pond. Frogs search for ponds with water but no fish to lay their eggs. When unwanted animals become established in ponds, they:

i.    Can predate upon the fingerlings,

ii.  Consume some of the fish feed, and

iii.              Compete for dissolved oxygen

This results in reduces fish survival, increase FCRs, and a slight reduction in carrying capacity due to competition. Consequently, depending on the severity, yields obtained are lower than would be expected. A pond full of tadpoles is especially disastrous if you are going to stock very young catfish fry.
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POND FERTILIZATION


FERTILIZING THE POND

    There is no need to fertilize ponds for catfish grow-out if the fish are fed on nutritionally-complete pellets. This is because all their food requirements are derived from the feed. Catfish grow-out monoculture pond fed nutritionally complete pellets only need to be limed if:

a.  The pond soils are acidic, pH 5 and below. In this case, lime with agricultural lime, preferably in the fine powder form by spreading uniformly over the pond bottom or pond.

b.  The pond cannot drain completely. In this case, lime the remaining puddles with builders lime (Ca (OH)2) or quick lime (CaO) until the water pH increases to 11. The objective of attaining such a high pH in this case is to kill off any fish frogs, potential diseases or parasites that might remain within the pond. Spread the lime over the pond bottom while paying extra attention to potential hiding places. This is necessary because any catfish left in a pond from a previous cycle can easily literally predate on all the new stock. After liming, the pond can be filled with water the following day but only stock it when the pH has decreased. 
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HOW TO PUT SCREEN IN OUTLET DURING POND CNSTRUCTION


SCREEN THE INLET AND OUTLET

The objective of screening is to prevent undesirable substances (fish and fish eggs, inclusive) from entering or leaving the pond without obstructing the flow of water. Therefore, the mesh size of the screen material should be small enough to prevent un-wanted substances passing through, while at the same time be large enough to allow water to flow through.

However, the efficiency with which the screen works, is not solely determined by the mesh size of the screening material. It is largely determined by the total surface area of the screen and the rate at which clogging occurs.

        SCREENING THE INLET

It is therefore, recommended that inlets be screened using a ‘filter sock’ made of fine mesh. In this way, a large surface area is provided and the rate of clogging significantly reduced because the debris collects at the tip of the sock. In this case, water will still flow un-obstructed from the top of the sock. Remember, it is not practical or possible to check the screen every hour and clean it. Screens tied flat tend to clog fast and do not allow water to flow through within a short period.

        SCREENING THE OUTLET

The outlet stand pipe, on the other hand, is best screened with cone mesh. Again, this increases the total screen surface area to ensure water can flow out with minimal clogging. Ensuring the outlet screen is in place prevents loss of feed during feeding and of fish during drainage. The stand pipe should be cut to the maximum height you would like to have water in the pond. Doing so prevents flooding beyond the levee wall, because the pond will start draining once it gets to

The desired water height.    However, for practical reasons, during the course of  production it is best to maintain the water level at about 10cm below the standpipe                  

Height. This is to act as a buffer in the event that it rains as it allows the pond room
to capture rainwater.

      MAINTENANCE OF SCREENS DURING THE COURSE OF PRODUCTION

     It is important to check all screens daily to ensure they are not clogged nor damaged. If there is a lot of debris, remove it and clean off the dirt by shaking and rinsing the screen. Do not shake the screen into the pond as the debris will only go back into the pond and re-clog the screen. Place the screen back immediately after cleaning. If damaged, repair or replace screens immediately. Damaged screens are an urgent matter. If you find fish or frogs in the screen, bury them as they are likely to find their way back into the ponds which is undesirable.
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DRAINAGE SYSTEM IN POND CONSTRUCTION


 THE POND BOTTOM AND ABILITY TO DRAIN

     The pond bottom should be smooth and firm. Pot-holes at the bottom provide shelter for fish to hide after ponds have been drained. Such fish, if not removed, will predate upon the new stocks, Survival rates for the new cycle will subsequently be lower with few very large shooters. The pot-holes also pose a danger to persons seining the pond who may trip and injure themselves. If the bottom is not firm, fish can hide in the mud. Thick layers of pond bottom mud not only have a negative effect on the pond productivity, but are also more difficult to seine. At drainage, a lot of fish also get trapped within the mud. Sampling and harvesting is therefore, more difficult and time-consuming in such ponds. It should be possible to completely drain and dry the pond bottom, after harvests and between cycles. This helps to ensure that all fish have harvested. Being able to drain ponds completely in between cycles makes it easier to undertake routine treatments and required maintenance work with better results. Preferably, ponds should be able to fill and drain completely by gravity to avoid pumping water, which is costly. Therefore, a pond bottom slope of 1-2% to the outlet is recommended. Ponds and drainage canals should also be constructed above the water table. Ponds constructed below or at the level of water table, are impossible to drain and dry completely. In addition, yields and returns from such ponds are poorer, because of the constant infiltration of cold, non-oxygenated sometimes acid water from water table into the pond during the course of production. Consequently, the quality of water within the pond becomes less suitable for production.

NOTE: All it takes is one catfish left in the mud, and the next round of fingerlings stocked in the pond after re-filling will be eaten by the remaining large catfish survival rate of the following cycle will be extremely low.

 HARVEST BASINS

Having a harvest basin set in the pond or between ponds is optional but recommended. Harvest basins make it possible to hold and handle fish alive while draining ponds. They also reduce the amount of labour required during complete pond harvests. A harvest basin can either be set within out outside the pond. Ponds that are to be drained frequently, for example nursery ponds, are much easier to harvest if they have a properly constructed harvest basin.

 SHAPE OF POND AND ITS ACCESSIBILTY

Typically, ponds are rectangular. Rectangular ponds are more practical construct, feed and manage. The narrower pond dimension dictates the size of the seine that will be needed. Therefore if one has ponds of several sizes on the farm, it is good idea to have them of similar widths, if possible so that the same seine can be used for all ponds. All   ponds on the farm should b e easily accessible for adding inputs and transporting harvested fish from the pond with relative ease and safety.

 OTHER STEPS INVOLVED IN PREPARING POND FOR STOCKING

Pond preparation for stocking marks the beginning of the ‘grow-out’ production cycle. Before the pond is socked for production, it should be prepared in the following way:


REMOVE EXCESSIVE SILT FROM POND BOTTOM

          The bottom of the pond bottom should be free of excessive amount of suit. It should also be dry and firm before filling. Silt removed should NOT be put at the top of the pond levee (as this increase the free board), but rather away from the ponds and / or used to repair the pond levee slopes. Remember, much of the bottom “silt” came from the slope of the leaves. It should, therefore, be put back form where it came. If the soil is heaped on top of the dykes, it will wash back into the pond when it rains. Because the bottom silt often contains high levels of nutrients, e.g. from leftover feed (if the person is a bad feeder) and feces, it is sometimes used to fertilize vegetable gardens. However, unless the feed input was excessive, the amount of nutrients in the silt is often not enough to justify the labor that is required to move the silt to a garden.

When soil builds up on the bottom of the pond, the pond becomes shallower. Over time, the bottom mud lowers water quality for production. This is of particular problem when a farmer over feeds the fish, which can often occur when sinking feed is being used.        After several seasons of mud build-up in the pond, the pond’s yield and carrying capacity for the new cycle will, therefore, be lower than that of the previous cycles. If there is no so much silt, the bottom can be left to dry until the surface cracks slightly before the pond is re-filled with water for the next cycle. The cracks allow air to enter between the mud and aerate it. Alternatively, the soil can be disked to aerate and increase the rate of decay of organic matter which in turn, reduces the rate of formation of substances such as hydrogen sulphide.

4.3.2  ENSURE THE POND IS NOT LEAKING

Repair all broken dam levees and make sure there is no seepage through the pond levees or around inlets or outlets.
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THE INLET AND OUTLET CONNECTION IN THE POND


THE INLET AND OUTLET

The diameter of the inlet pipe should be less than that of the outlet pipe in order to prevent overflow from the pond in the event that someone accidentally leaves the inlet open. The inlet pipe should be at least 20cm above the water surface to prevent fish from escaping. If the inlet is set at or near the level of the water, fish will swim against the current of the inflowing water and escape from the pond. When the inlet is above the water level and properly screened, fish are unable to jump into the pipe ad escape through the inlet pipe. The screen as inlets to commercial ponds. Such channels are difficult to screen effectively catfish are more likely to escape from the pond through then inlet as opposed to climbing out of it on the pond sides.

The also escape when the pond overflows totally due to a blocked standpipe, during heavy rains. Old literature recommends that the pond inlet and outlet be located at opposite ends of the pond to facilitate flushing (good water in and poor water out) when poor water quality becomes an issue. However, this is not all that important if you flush the recommended way (see chapter 5). Pond outlets should have anti-seep collar and an anchor-collar. The anti-seep collar prevents water seepage from the “joint” where the outlet pipe and clay soil meet. These two substances do not bond together and water tends to follow the outside of the pipe unless interrupted by an anti-seep collar. Anti-seep collars are standard construction principles but have been ignored in most pond construction and most ponds have leaks as a result. When not in use, the drain pipe is full of air, which makes the pipe tend to float. If the PVC pipe is not secured at the pond bottom, the pipe can be dislodged at the bend or leaks can develop due to the pipe floating up slightly. Having an anchor- collar just after the pipe bend prevents this by keeping the drain pipe and its bend down.

4.2.5 THE FREE-BOARD HEIGHT

The recommended freeboard height is 20 to 30cm for the following reason:

a.  It allows for more free movement of air currents above the pond water surface which improves mixing and oxygenation of the water.

b.  It becomes easy to undertake routine tasks such as feeding, seining, checking water quality and removing dead fish.

c.   It is cheaper to construct and maintain

d.  There is less surface area for erosion into the pond. Therefore, this contributes less eroded silt to the pond water and soil. However in ponds of over one hectare a freeboard of up to 50cm can be accommodated (table 4.2)

Table 4.2 Recommended free-board height for catfish grow-out ponds

Pond size rang
Freeboard Height
·  Smaller ponds (100m2 up to 1 ha)
·  Large ponds (> 1ha)
·  20 to 30 cm freeboard is sufficient
·  50 cm is recommended because there can large be waves on the pond

It is undesirable to have a free-board higher than what is recommended because:

a.  It is an unnecessary added construction cost – expensive to make.

b.  It attracts predators and burrowing animal such as nutria and muskrats.

c.   High freeboards above the water favor the nesting flying ants and termites, which later leads to leaks.

d.  It makes working on the pond difficult and dangerous.

e.   A high freeboard prevents air currents from reaching water surface, thereby preventing mixing and reducing oxygen exchange.

f.    Looks ridiculous.
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AVERAGE WATER DEPTH IN A POND


     AVERAGE WATER DEPTH

The recommended average water depth is 1 meter for non-aerated static water ponds. The water depth in the pond should be at least 80 cm at the inlet and no more than 1.2m at the outlet.

The Maximum Water Depth for static water pond production is determined by the distance sunlight can penetrate into the water column. This is because photosynthesis can occur in the water column up to twice the depth the sun’s rays can penetrate. In ponds, sunlight can generally penetrate to a depth of about 30-80cm depending on the levels of water turbidity. The oxygen generated during the process of photosynthesis then dissolves into this section of the water.

In addition, the sun’s rays warm u p the water. Hence, the upper water column in ponds has the best conditions for fish production. For this reason, a maximum water depth of 1.2m id recommended. Beyond this depth, pond waters start becoming devoid of oxygen and stay cooler. Ponds thermally stratify from about 1.2m water depth downwards. This means that the temperature and quality of the top 1.2m of water will be distinctly different from that of the water below 1.2m deep. When the pond is deeper than 2 meters, the total volume of bottom zero-oxygen water is greater than that of the water containing oxygen. Incidences of fish kills consequently, become more likely when there is a change in weather (for instance when it rains, it is windy, it becomes cold, etc). This is because, the cool rain causes the oxygen rich water at the surface to go down and in the process, the oxygen-deficient water from the bottom is pushed up. The mixing of the oxygen-deficient water from the bottom with the rest of the pond water results into an overall total oxygen depletion. When this happens, the farmer observes that fish which showed no signs of stress the previous day, or a few hours ago, are suddenly all dead and floating on top of the pond. Even though catfish above 100 g can survive water deficient in oxygen for a while by breathing atmospheric air, there is also the additional risk of the mixing of hydrogen sulfide and other toxic chemicals that may be present in the deep, zero-oxygen layer. Hydrogen sulphide is lethal to fish, even in extremely small amounts. See chapter 7 for more details on water quality requirements for catfish production.

     Therefore, there is no added advantage in having a pond with a water depth greater than 1.2m. The deeper the pond is, the more expensive it is to construct, and the riskier it becomes to manage water quality because stratification becomes more likely – unless one has equipment to mechanically mix and aerate the water. Such equipment is expensive and requires a reliable source of power. In addition, for the current farm gate price offered for table sized catfish in Nigeria, it does not yet make economic sense to invest in mechanical aerators for grow-out ponds.

The Minimum Water Depth in a pond should be not les than 60 cm. When the pond water depth is less than 60 cm:

a.  The pond’s carrying capacity is reduced considerable. For catfish ponds, the total volume is very important because the water dilutes the catfish waters. Because catfish can breathe air after they have surpassed the fingerling stage (i.e. from + 100g), waste build-up becomes the first limiting factor. Shallow ponds have less water volume than deep ponds and therefore have a lower carrying capacity. This means fewer kilograms of fish can be harvested from the same pond area. Having the recommended depth therefore, increase potential to harvest more kilograms of fish from the same pond, making it more productive.

b. It is easy for wading birds, such as the marabou stork and heron to enter the pond, scare predate upon the fish. Such birds can only enter ponds they can step down in.

c.   Aquatic weeds are more likely to grow in shallow ponds. Excess weeds in the pond interfere with seining and reduce the levels of dissolved oxygen available for fish production. Consequently, FCRs are likely to increase and pond yields to decline.
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THE SLOP OF THE POND LEVEE


THE SLOPE OF THE POND LEVEE

The slope of the pond levee, is the gradient of the levee from the edge of the top width to the inside toe at the bottom of the pond. It is described as the ratio between the horizontal distance and vertical height of the dam levee. This means, for instance, that if the distance from the inside toe to where the top width starts (edge of the pond from above) measures 2m and the height of the dam measures 1 meter, then the slope for that levee is 2:1.

It is recommended that pond levees have a gentle slope of about 2:1. This however, depends on the size of the pond. Large ponds need to have a gentler slope (see table 4.1 below)

Table 4.1: Recommended Slope for production ponds

Size of Pond
Recommended Slope
5 – 20 ha
4:1 to 7:1
1500  m2 to 5,000  m2
2:1 to 4:1
+150  m2 to 1,500  m2
2:1
≤ 150  m2
1.5:1 to 1:1

          Remember, the large the pond, the gentler the slope should be. Large ponds have a greater surface area to perimeter ratio. This makes it possible to obtain the greater amounts of earth needed to make gentler slope from within the ponds have a greater surface area to perimeter ratio. The makes it possible to obtain the greater amounts of earth needed to make gentler slopes from within the pond during construction. Having a gentle slope is beneficial in that:

a.     A gentle slope helps break up the waves as they hit upon the pond levee. This reduces the impact of the water waves on the levee.  Consequently, the levee is less likely to collapse and there is less siltation of the pond. The lifespan of the pond is also subsequently increased and maintenance costs are lower. Better yields (in as far as the pond infrastructure is concerned) can therefore be sustained beyond one cycle. The ability of catfish to make a deep ‘catfish highway’ will also be minimized.

b.     It is easier and safer to enter into and out of the pond to undertake activities such as seining. One should be able to actually walk into and out of a pond and not have to ‘jump in and climb out’ of the pond. The latter is dangerous for personnel.

c.      It makes it easier to seine the pond and land the seine. Significant environmental benefits are derived when pond levees are constructed as recommended with the appropriate slopes. There is less pond siltation when levees are constructed as recommended.

Consequently, there is also a reduction in the level of suspended solids in pond effluent water. In addition, less water is required for production due to reduced seepage.
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STEP -BY - STEP IN POND CONSTRUCTION


RECOMMENDED STEP-BY-STEP POND CONSTRUCTION

Recommended pond standards are discussed below in relation to management and production potential and in accordance with Department of Fisheries and Allied Aquacultures, Auburn University, Alabama, USA.

         POND LEVELS (DYKES)

The pond’s sides are called levees or dykes. The pond levees should be well compacted and have a gentle slope. The greater the degree of compaction, the stronger the levees will be. Thus, during construction, one should lay down about 15 cm of soil which, when compacted will become about 10 cm high. There should be no stumps or debris left within the pond levees. Soil should be compacted shortly after it is laid to prevent hardening (some soil become rock-like if they are allowed to harden). The level of compaction achieved when constructing the pond levees affects pond management and production as follows:

a.                 Poorly compacted levees are weaker and often collapse during the course of production when wind pushes the water and causes waves to wash against the levees thus eroding them. When pond levees collapse during the course of production:

Ø The ponds become shallower which lowers the ponds’ carrying capacity.

Ø There is increased siltation and clay turbidity which have a negative effect on water quality for production.
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