1. When farming fish, it may at times be necessary to hold fish alive for several days, outside their normal rearing facilities, for example:
2. Storage facilities are specifically for holding fish temporarily; to keep costs down, quite high stocking densities are used; usually storage does not exceed one week. As the fish are stocked at a high density, it is best not to feed them, to reduce dissolved oxygen consumption and water pollution.
3. To hold your fish alive successfully, plan your storage well:
(a) You will need an ample supply of well-oxygenated water. Use aeration if necessary to maintain good water quality.
(b) Fish transport should be fast: locate storage close to harvesting sites and ensure easy accessibility by whatever transport means you choose.
(c) Simplify harvesting and handling as much as possible, to reduce stress and damage to the fish.
(d) Protect your stored fish well, against predation and theft, for example by fencing (see Section 4.5) and by special devices against bird predation (see Section 4.8).
(e) Adapt the stocking rate of the fish in the storage facility according to the conditions: water temperature, dissolved oxygen availability, water exchange rate, length of storage and kind of fish. Under the best conditions of cool, well-oxygenated water and short storage time, you may store:
4. In net enclosures or cages, water is exchanged by local currents, or by the movement of the fish themselves. Check that the fish are reasonably active, that netting is clean and allows water exchange, and that external water quality is good.
5. As an approximate guide, you will need in tanks or ponds a water flow of:
6. Aeration is usually provided in small areas with a simple air pump and porous piping, to supply a steady flow of air bubbles. For good aeration the water should be stirred by the bubbles to a steady but gentle "boiling" level through most of the area. For moderate aeration this level of aeration is provided for over one-third to one-half of the area, or is spread over the area to create fairly quiet, undisturbed conditions.
7. As an appropriate guide, a 300 W (0.4 hp) air pump will give:
1. There are several ways to use existing farm structures such as ponds and water canals for temporary holdings of fish. You may use one of the following, according to your needs:
2. The net enclosure can be one of the following:
3. Remember to adapt the mesh size to the size of fish you have to hold. Some grading can be done at the same time if necessary (see Section 12.3 for example).
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Live fish storage using net enclosures: some examples
1 Wood frame and net
bag: similar to the single enclosure incubator shown in section
9.3, para. 9
2 Free standing wooden poles with suspended net bag: similar to the incubators
shown in section 9.3
3 Oblique poles in side of pond with suspended nets: a quick and simple method
4 Nets hung in a water canal: another quick and simple method
1. When large quantities of fish have to be regularly stored, it is useful to build more permanent and specialized storage facilities. Design them as suggested above (see Section 13.0) so that:
2. Average stocking densities according to kind of fish and water quality are suggested in Table 31 for guidance only. There are basically two kinds of permanent storage structure, basins (tanks) and ponds. There are several ways to build these as you can see from the examples given below.
3. Storage basins made of earth, bricks or cement blocks are usually designed as elongated structures through which a good water flow can be maintained.
4. Separate batches of fish can be held in a series of storage nets hanging from the sides of the basin, or in individual pockets made from a seine net and horizontal supports (see Section 13.1).
5. Storage tanks can easily be built from brick or cement blocks, as explained earlier for permanent harvesting basins (see Section 11.3). Make inside walls very smooth to reduce injuries to the fish. Wooden boards and screens may be used to subdivide these tanks as necessary, as well as to regulate their water depth.
Note: particles can dissolve from newly constructed storage structures with cemented inside walls. Before being used for fish, these structures should be flushed out with water, either with a continuous flow (allow at least 20 complete exchanges) or by repeatedly filling, allowing water to stand for three to four hours and draining at least 15 times. If in doubt, store a few fish for several days to make sure there are no ill effects.
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6. According to the type of fish ponds on your fish farm (see Section 1.3,Construction, 20) you can design storage ponds in different ways:
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7. The individual size of storage ponds depends on the weight of fish to be held in each of them. Under available storage conditions, you can estimate your needs on the basis of the average stocking densities given in Table 31.
Example
You will need to hold alive a maximum of 2 000 kg of market-size tilapia for four days at most, in the presence of a moderate water exchange, about 10 l/s equivalent to 0.3 I/min/kg fish in this case.
Which size of storage do you require?
