Small-scale freshwater fish farming

Before a farmer starts fish farming, there are several basic considerations to ensure success. These include:

Pond design

When deciding on the pond site and design, there are some factors to be considered. Some of these are:

a) Source of water to fill the pond and how the same water will be brought to the pond:

The general rule is that the pond water inflow and outflow should equal the pond volume over the period of a month.

If the inflow is too low, water quality may suffer from oxygen depletion and/or accumulation of toxicants.

If the water outflow is too high, large amounts of beneficial algae may be flushed out from the pond.

The water should keep the pond full throughout the culture period. The pond should fill up in less than a week.

Place screens on pond inlets and outlets to keep out predators, insects and unwanted fish and also to retain the cultured fish.

b) Size, shape and depth of the pond:

Relatively shallow ponds are productive. However, the shallow end should be at least 0.5m deep to avoid invasion by weeds and predation of the fish.

The size and shape of the pond can vary depending on the fish species, fish population and the farmer’s preferences.

It’s worth noting that if you want to produce fingerlings, you will require more small ponds whereas a food fish producer requires relatively large ponds.

c) Slope of the pond bottom:

The bottom must have a sufficient slope for good drainage. A slope with a drop of 2cm for every 10m along the pond bottom is appropriate. If the slope is too gentle, the pond will not be easily drained. If the pond is too steep, it may be too shallow at one end or too deep at the other end. Pond should be drainable.

d) Height, width and slope of the dyke:

The perimeter and feeder roads are required for movement of machines during construction and harvest.

If you plan to drive on the dykes, build them at least 3m wide on top and at the base.

e) Soil types:

Top soil is high in organic material and should not be used to construct pond dykes. Land should be composed of good quality soil, with little or no gravel or rocks either on the surface or mixed in. Areas with rocky, gravelly, or sandy soil are not suitable for pond construction. Soil that will be used to build the dykes must contain at least 20 percent clay so the finished pond will hold water throughout the growing period.

Fish Species suitable for culture in Zambia

There are three major fish species which can do well with the Zambian climatic conditions. They are Nile tilapia (Oreochromis niloticus), African catfish (Clarias gariepinus) and Trout.

a) Tilapia

This is a warm water fish and is mainly cultured in fresh water environment. It thrives well in water temperature of between 20 to 35 degree Celsius. It attains sexual maturity at two months. Tilapia feeds lower in the food chain i.e. feeds mainly on phytoplankton, zooplankton and detritus.

Stocking rates range from two to six fingerlings/m², depending on the level of management. Male tilapia are known to grow almost twice as fast as females.

It is therefore preferable to stock only males (monosex culture) to achieve the fastest growth and reach market size in the shortest possible period, resulting in more proteins and profits. A major management problem of pond-cultured tilapia is excessive reproduction and the subsequent stunting of fish due to overcrowding.

Methods of controlling overpopulation include manual sexing of fish, use of sex-reversal hormones to produce all males, and use of predators.

The success of these methods may rest with how well a fish farmer understands the techniques.

b) Catfish

It grows in the same agro climatic regions as tilapia. The water temperatures of between 26 to 33 degrees Celsius are ideal. It attains maturity at two years of age or at 200 to 500 grams. It feeds mainly on zooplanktons. Their stocking rate is 100 to 450 fry/m².

Catfish has a drawback of high mortality of fry especially during the first 14 days after eggs hatch.

c) Trout

It’s a cold water fish and it’s best grown in high altitude regions where water is cooler. It’s presently limited by availability of seeds and quality feeds in the country.

Pond preparation for stocking

The procedure below should be followed by the farmer to the latter when preparing the pond for stocking. These steps will help boost the productivity of the pond.

For an old pond, drain all water and allow it to dry for 14 days.

Apply lime to the pond bottom and dyke slopes. Choose agricultural limestone (CaCO₃) for application in your fishpond.

Apply organic fertiliser in the pond before filling it with water. The most common examples of organic fertilisers are animal manures (from cattle, poultry, donkeys, rabbits, sheep and goats) and decaying plant matter, such as cut grasses.

Fill the pond with water

Apply inorganic fertiliser in the pond after it has been filled. Apply DAP and UREA to your fishpond at the following rates: DAP: 2g/m²/week (or weekly applications of 15 tablespoons DAP for every 100m²). UREA: 3g/m²/week (or weekly applications of 30 tablespoons urea for every 100m²).

Fish feeds

There are various feeds that can be offered to the fish in the pond. Some commonly available feeds include:

i. Meals

ii. Crumble

iii. Dry sinking pellets

iv. Moist sinking pellets

v. Floating pellets

The feeds can be formulated so as to meet the body requirements of the fish species. This can be done as follows:

i. Cotton seed cake — 37%

ii. Wheat bran — 57%

iii. Fresh shrimp — 6%

iv. Vitamin premix

Feed ingredients can be hand ground or a manual grinder can be used. It’s important to adhere to the four fixes (4Fs) when feeding fish. These are:

·         Fixed feed quality.

·         Fixed feed quantity.

·         Fixed feeding location.

·         Fixed feeding time.

The fish should be fed between 10am and 4pm when the water temperatures and dissolved oxygen content are reasonably high and the fish are active.

Fish farming is a very profitable enterprise if done with good management. Farmers should develop passion towards this less exploited agricultural opportunity. Join me next week as we go through handling, seed production, marketing, hatchery management and fish farming economics among other topics on aquaculture.

About the author: Cheruiyot J. B teaches in the Department of Animal Sciences at Egerton University.