It is usually not a good practice to extend the pond area to the waters edge along the sea or a major river or canal. A buffer zone should be left for protection against erosion. Mangrove should not be cleared from these areas, and if no vegetation is growing, some should be planted.
Small streams, or other paths of runoff, should not be blocked unless a water diversion canal is constructed to carry off drainage water. Water which can not be drained from areas adjacent to ponds can sometimes seep into a pond in sufficient volume so that the pond bottom cannot be dried.
If it can be located elsewhere, the main water supply gate should not be located either at a bend in a river or facing the open sea. These areas are subject to strong currents and wave action which can cause damage to the gate which result in costly repairs.
It is important to place the sluice gate so incoming water sets up a good circulation of water within a pond. This is best achieved by placing the gates near the corner on the short side of a pond. This is an important point, because letting in water is sometimes the only way to break up stratified pond water and prevent shrimp die-offs.
Areas with a high level of silt or mud in the incoming water have special problems. Ponds with internal canals along the dikes are good, because under this condition, the sediments are eventually deposited in the canals where they can be most easily removed. In an area facing a mud flat, it may be necessary to construct a small setting pond in which the silt can be trapped before the water enters the growing pond.
If possible, shrimp ponds should have separate water intake and discharge canals. Water should be taken in at one corner of a pond and discharged from the opposite corner. This is especially important for large pond complexes with extensive canal systems.
A single canal for intake and discharge of water from a pond complex has the following disadvantages:
All water drained from the ponds is usually not completely discharged from the canal and some of it will reenter the ponds the next time water is taken in.
The spread of disease from one pond to another is encouraged because water from one pond can enter another.
Water that is fouled with H2S, ammonia or other contaminants can move from one pond to another.
There can be a conflict between farmers concerning usage. For instance, one farmer might want water in the supply canal high so he can harvest milkfish, while another farmer wants the water level low so he can harvest shrimp.
If a single gate is used for both intake and discharge water, exchange within the pond will be poor. Water at the far end is just moved toward the front during draining and then pushed back when new water is taken in.
Separate water intake and discharge canals in a pond complex have the following advantages:
Ponds can be filled better and water will not be contaminated by the discharge from other ponds.
The chance of spreading disease is reduced greatly.
A constant head can be maintained in the intake canal. This can reduce water loss through leaks in the pond dikes. It also cuts down seepage of water through the dikes and consequently reduces leaching of acid into the ponds from dikes with acid sulfate soils.
No conflict of usage should occur between farmers.
A better exchange of water is provided for individual ponds.
Flow-through systems can be used. With pumping, a constant head for continuous flow-through can be maintained.
It was brought out during the discussion that shrimp in extensive ponds with no feeding, generally grow well for two months, but after that time, growth is reduced greatly. If the shrimp are placed in another pond with a good supply of natural food, fast growth is resumed. Thus, it appears that a progressive method of shrimp culture is advisable when no supplementary feeding is practiced. For growing to a medium size, a two-stage progression composed of a nursery pond (NP) and a rearing pond (RP) is adequate. For growth to a large size, a three-stage progression composed of a nursery pond, a transition pond (TP), and a rearing pond would be preferable. It is difficult to transfer shrimp from one pond to another without killing or injuring a number of them. See Section 7.6, transferring fry from nursery to growing ponds.
The following design criteria are suggested for progression type pond systems:
The NP, TP, and RP ponds should be adjacent.
The pond bottom elevation should decrease from NP to TP to RP to permit drainage of water and aid in the transfer of shrimp.
The bottom should be contoured to permit adequate drainage so the shrimp will move to the sluice gate and on to the next pond as a pond is drained.
The total area must be used all, or almost all, of the time.
If possible, nursery ponds should not be adjacent to large perimeter dikes. This is because the large surface area for runoff increases the chances for undesirable substances such as silt, acid, etc. to be washed into the nursery. Also, if there are crab holes or other leaks in the periperal dikes, the fry could escape, or predators could enter. Small predators which could enter through a hold would not be much of a problem in a grow-out pond, but they could be dangerous in a nursery.
In polyculture operations fish fry and shrimp fry should have separate nurseries.
In monoculture operations, the yield from one nursery pond should go to one rearing pond. This is because it is difficult to estimate numbers if the harvest from one nursery is split between two or more rearing ponds.
The nursery is operated continuously and drained into the rearing ponds on a monthly rotation scheme so that the total area of rearing ponds is in almost continuous use. The recommended size relation of the ponds to each other is : NP = 1, RP = 3. The growing period in the nursery pond is one month and in the rearing ponds is three months. A layout of this type is shown in Figure 1.
In this system, the shrimp are moved progressively from the NP to the TP to the RP on a set time schedule as they grow larger. A layout of this type is shown in Figure 2. The relative size of pond units and a suggested scheme of management for P. monodon culture is as follows:
| Type of pond | Relative size of pond | Growing period (mos.) | Stocking rate (No./ha) | Size of shrimp (g) | |
| at stocking | at harvest | ||||
| Nursery | 1 | 2 | 58 000 | 1 | 8 |
| Transition | 3 | 2 | 18 000 | 8 | 22 |
| Rearing | 8 | 2 | 12 000 | 22 | 33 |
