Introduction: The objective of spawn rearing in nursery ponds is to raise maximum number of fish fry in minimum water area. When newly constructed, an area of 0.04 ha (25 Χ 16 m or 20 Χ 20 m) in area and having 0.8 m to 1m depth of water is an ideal size. However, any pond practice conforming ton the above specifications would be ideally suited to nursery requirement. In practice, however, even 4-6 times larger and 2-3 times dipper ponds are used as nursery ponds. Nursery ponds should be free from over flooding, heavy seepage or sudden fluctuations of water level. Inlets and outlets are most undesirable.

Stocking : Spawn should be stocked at a rate of 5-10m/ha. Preferably stocking should be done in the morning or late in the evening when the water temp is low. Spawn must not be stocked during mid-day.

Size and Depth :  0.04 - 0.06 ha. (size)  0.75-1 m depth.

Pre-Stoking Management :

Eradication of Weeds :  All kinds of weeds, marginal sub-merged, floating and rooted should be removed thoroughly by manual labour. Application of chemical should be avoided.

Eradication of Predatory and trash fish :  In perennial ponds, predatory and weed fishes would take direct toll of tender spawn, while trash/weed fish would not compete with spawn for planktonic food and the two together for space oxygen and supplementary feed and hence need to be controlled by application of mahua oil cake @ 2500 kg./ha-m followed by bleaching powder @ 175 kg/ha-m the next day. This kills all the fishes. The ponds become ready for stocking of fish after 6-7 days. For seasonal ponds mohua oil cake is normally not applied.

Liming :  Liming is not essential in ponds where soil/water pH is in acidic range but also in pond where it is slightly alkaline range with a view to control fish parasites and diseases, and meets lime deficiency likely to be created by the application of organic and inorganic fertilizers. Lime should not be applied in ponds where the soil/water pH is above 8.5. Normally, the dose of lime in nurseries varies from 1000-1500 kg/ha.

Eradication of aquatic insects and larvae :  All aquatic insects and larvae should be killed before stocking. This can be achieved by the application of soap oil-emulsion (18 kg. ordinary detergent powder is mixed with 56 litres of diesel oil to make an emulsion to be applied/ha). This should be applied at least 12 hours before stocking.

Stocking : Spawn should be stocked at a rate of 5-10m/ha. Preferably stocking should be done in the morning or late in the evening when the water temp is low. Spawn must not be stocked during mid-day.

Culture duration : 12 days. Spawn grows to 20-25 mm size weighing 200-300 mg. each.

Post-Stoking Management :

Supplementary feeding : Supplementary feeding is required to enhance the growth of the stocking material. In case of spawn a mixture of oil-cake: rice polish at 1:1 is applied in powder form. The rate of feed is for first 5 days four times the weight of spawn during second 5 days at eight times the weight of spawn. On eleventh day no feed should be applied and on twelfth day, the fry (20-25 mm.) should be harvested. One spawn weighs 0.0014g.

Harvesting : On twelveth day by repeated netting only.

Quick Preparation Of Nursery Ponds For Subsequent Crops -

After harvesting of the first crop of fry from the nursery, the pond may be prepared to raise subsequent crops as follows:

• Apply single Superphosphate at 150 kg/ha, RCD 700 kg/ha, GOC 700kg/ha, add 30-50 ml. of live plankton/ha. On first day.

•  Second day : No manuring-stock with spawn.

• Third day : RCD-87.5 kg/ha., GOC-350.0 kg/ha.

• Fourth day : RCD-43.75 kg/ha, GOC-175.0 kg/ha.Fifth day to tenth day (daily): RCD-22.0 kg/ha., GOC-87.5 kg/ha, Ricebran 100.0 kg/ha

• Eleventh day : no feed

• Twelfth day : harvest.

In this way 3-4 crops of fry may be raised from a single pond.