Integrated agriculture-aquaculture: A primer

Nursery system for carp species

by Md. Golam Azam Khan

Anursery is a facility where fish seed (spawn, hatchlings or fry) can grow. Efficient fishpond culture requires special preparation of nurseries for receiving spawn and hatchlings. The ideal size of a nursery is 0.02-0.05 ha with a depth of 1.0-1.5 m. The following is an example of a 0.02-ha nursery as prepared in Bangladesh for 15-20 days.

Pond preparation

Remove all aquatic weeds (day 1).
Drain and dry the pond.
Apply 5-6 kg lime/200 m² which helps release food nutrients available and kills pathogenic organisms in the pond (days 3 to 16).
Refill water if necessary and fertilize (day 19).
To determine if enough food organisms (plankton) for the fish fry have developed in the pond, the most basic and reliable test involves filtering approximately 50 litres of water through a fine mesh net or cloth into a 2.5 cm diameter specimen tube. Alternatively, a very simple field test in nonmuddy water is to dip one's hand in the water to the elbow. If the hand is no longer visible, the plankton is probably sufficient.

Stocking

Apply 80-100 g insecticide (e.g. Dipterex) at least 20-24 hours before stocking to kill the back-swimmers or other aquatic insects in the pond (day 29).
Stock 60 000-70 000 hatchlings/200 m² of 4-5 days age (200-250 g). The hatchlings should be of same age, uniform size, vigorous and released either in morning or late afternoon (day 30). Common carp seed is available throughout the year in Bangladesh.

Before the hatchlings/fry are introduced to a new environment, it is important that the temperature inside the plastic bag is approximately the same as the pond water.

Place the bags, unopened, in the pond for 10-15 minutes. Open slowly and introduce small quantities of pond water to equalize the temperature. The fry is now allowed to swim into the pond.

Feeding

It is often difficult to maintain a high level of natural food for growing fry so that supplementary feeds become necessary (day 31). A mixture of finely powdered oil cake (soya beans, mustard, etc.), rice or wheat bran and fish meal in the ratio of 5:4:1 is to be supplied to fry, at 200 g divided into several portions per day.

Fertilization

Fertilization is necessary to maintain an adequate level of natural food organisms in the pond.

Care of fry/fingerlings

Check the pond daily and see if there is an excess of green algae. If so, discontinue application of supplementary feeds. Remove frogs/snakes, if any, in the pond. Increase feed by 10 percent of the rate mentioned above if the growth of the fish is not found steady and good.

Harvesting and transportation

Harvest the fry/fingerlings (day 60) by using a fry catching net, either in the morning or late afternoon and keep them in the enclosure (hapa) or cistern at least 3-4 hours before transportation (day 60). Transport the fry/fingerlings in oxygenated plastic bags.

Before transporting, it is important that fingerlings are conditioned. The principle behind this is that they have time to empty their guts before being packed in high densities, so that the pollution of the water in the transport container through excreta is reduced. Clean water from a tube well should be used for conditioning the fingerlings.

Traditionally, young fish are transported in clay or aluminum pots. Recently, the use of plastic bags with compressed oxygen is becoming more widespread, as this allows the fish to be transported in higher densities and longer distances with substantially less mortality. Approximately, 5 litres of water and 15 litres of oxygen are placed in each bag (assuming plastic bag volume is 20 litres).

Budget (in Taka) for a 0.02 ha nursery pond preparation for fingerling production

Costs
Draining/refilling or poisoning of pond	75
Lime (5 kg)	25
Cattle dung (200 kg)	100
1.75 kg urea and 2 kg triplesuperphosphate	20
Dipterex 0.2 kg	80
60 000 carp hatchlings	600
Supplementary feeds: 20 kg mustard oil cake + 10 kg rice or wheat bran and 4 kg fish meal	180
Netting, labour and others	400
Total	1 480
Income from sale of 30 000 (3.5 - 4.5 cm) fry/fingerlings	3 000
Balance	1 520
1992: US$1 = TK38

Issues for further consideration

From experience, farmers who adopt these techniques are relatively resource-rich and/or have had access to specialized information. Options for sanitation of nursery ponds (e.g. to eradicate aquatic insects that prey on fish larvae) that do not involve the use of dangerous chemicals should be used, e.g. higher levels of quicklime, eradication of pest habitat and continual trapping and removal of pests, etc.

Many nursery operators do not have access to tube-well water, and to condition fish under this situation, farmers may need more detailed information. The conditioning process has more important details, such as what exactly is done and what fish are in good condition and suitable for transporting.

The role of women may be very marginal in Bangladesh nursery systems (from where this example is taken) but in other locations in Asia they represent a major part of the labour force. The methods described are broadly similar to those used elsewhere by commercial nursery operators although they tend to be most intensive in Bangladesh. There they also use the practice of fry and fingerling production in the same pond (one-tier system) in bigger ponds.

The practice of fish seed rearing is followed by a large number of small-scale farmers in Bangladesh, who themselves do not necessarily grow fish to market size. This part-time occupation may be an option for other farm families in areas where the availability of fish seed is still a limitation in the popularization of aquaculture.