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Nam Sai can produce cages to any size, shape and depth. They can be made in many types of material, including knotted and knotless mesh from 1 cm upwards. They take more time and are more difficult to make than hapas, as they cannot be simply stitched with a sewing machine. For this reason they are more expensive and more time will be needed to complete an order.

Cages:   Cages are usually made from large mesh netting (1.5 cm upwards) and are suspended from a floating structure of some sort. They are best used in rivers and lakes for grow-out purposes, but can be used in earth ponds, such as in farm reservoirs. Fish densities of 15-30 kg per m3 can be supported, depending on water quality, water flow rate and depth. Large fingerlings (perhaps pre-nursed in hapas) are stocked to avoid fish escaping through the mesh. Polyethylene net is most commonly used, as it is very robust and UV tolerant. Fouling is not a problem in cages with large mesh size (over 2 cm) and cleaning is not necessary after use. They are simply dried and then repaired.

Hapas and Cages

Hapas:    Hapas are cages, usually made from fine mesh, that can be set up in any shallow pond, canal or ditch. They are fixed to poles pushed into the pond bottom and are only suitable for shallow water (less than 1.6m) with low water flow rate and level fluctuation. All spawning, sex reversal and nursery operations at Nam Sai are carried out in hapas fixed to bamboo poles that provide flexibility in high wind. They are cheap, durable and quick to set up a matter of minutes. Harvesting of fish is simple using a bamboo pole to confine the fish in one corner. They are easily cleaned by scrubbing with a hard brush whilst washing with pond water.

Hapas are not suitable for growing fish to market size, as they are fouled quite quickly and water exchange is insufficient to maintain very high stocking densities. Nevertheless, there is sufficient oxygen supply for moderate stocking densities (0.5 to 2 kg per m3) and ammonia and nitrite build up is not a problem. Natural food is also available in hapas, as phytoplankton and other small food particles can pass through the material and the material itself provides a surface for algal growth. This can be enhanced by using chemical fertiliser to promote phytoplankton growth, a technique particularly useful with tilapia.

Hapas can be used for other aquatic animals, such as prawns, shrimp, frogs, fancy fish, etc. Grading, vaccination and handling of fish is made easy with hapas. They are often fitted inside rearing tanks to make harvest of fish simple.
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The hapas produced by Nam Sai are constructed from only the best quality nylon material and twine. This is important if they are to withstand strong UV light and the destructive, gale-force winds associated with early monsoon rains. They are available in standard sizes of 5, 6, 10, 20, 40 and 120 m2 with 90 cm depth, but can be made to any size and shape specification. All the hapas that we use are made from 20 strands of nylon per inch (S.P.I) material (both fry and brood fish), but they can be made in smaller or larger mesh sizes. 20 S.P.I. material is robust and doesn't foul too quickly. Tilapia swim-up fry can be stocked without fish escaping. 16 S.P.I. material is less robust and sometimes used for nursing larger fry to fingerlings. 24 S.P.I. or smaller is very robust, but is fouled very quickly. It is useful for nursing hatchlings of fish species that are quite small.
Standard hapas:
      Hapa size     (m2)
Dimensions    (m)
Volume  (m3)
  Weight   (kg)
5

2.8 x 1.8

0.024
2.1
6.25
2.5 x 2.5
0.024
2.5
10
2.5 x 4.0
0.027
3.1
20
2.5 x 8.0
0.055
5.5
40

5.0 x 8.0

0.080
10.0
120
5.0 x 24.0
0.240
27.0

Please note that when calculating freight costs, the volume is used, as hapas are quite light. For converting volumes to weight, divide the volume in m3 by 0.006.

Please note that all equipment exports are now handled by Mr.Angus MacNiven at Baan Pramong Co.Ltd. A new website www.farmaqua.com has been established for this purpose. Customers will be pleased to hear that the range of equipment now supplied has been increased.