In artisanal salt works ponds are only a few hundred square meters in size and have depths of 0.1 to 0.6 m.
Lay-out of a typical artisanal salt farm (Vinh Tien salt co-operative - Vietnam).
Most salt farms only operate during a few months, when the balance evaporation/precipitation is positive. Salt production is abandoned during the rainy season, when evaporation ponds are often turned into fish/shrimp ponds.
Although salt production in these salt streets is based on the same chemical and biological principles as in the large salt farms, production methods differ slightly (Vu Do Quynh and Nguyen Ngoc Lam, 1987).
At the beginning of the production season all ponds are filled with sea water. Water is supplied by tidal inflow, but small portable pumps, wind mills and/or manually operated water-scoopers are also used, allowing for better manipulation of water and salinity levels.
Water evaporates and, usually just before the next spring tide, all the water, now having a higher salinity than sea water, is concentrated in one pond. All other ponds are re-filled with sea water, which once again is evaporated and concentrated in a second pond. This process is repeated until a series of ponds is obtained in which salinity increases progressively, but not necessarily gradually!
For the remainder of the season water is kept in each pond until the salinity reaches a predetermined level and is then allowed to flow into the next pond holding water of a higher salinity. Note that the salinity in the different ponds is not kept constant as in permanently operated salt works. Sometimes, to further increase evaporation, ponds are not refilled immediately but left dry for one or two days. During that time the bottom heats up, which further enhances evaporation. Once the salinity reaches 260 g.l-1, water is pumped to the crystallizers, where the sodium chloride precipitates. Artemia thrive in ponds where salinity is high enough to exclude predators (between 70 g.l-1 and 140 g.l-1).
As seasonal systems often are small they are fairly easy to manipulate. Hence higher food levels and thus higher animal densities can be maintained. Also, factors such as temperature (shallow ponds), oxygen level (high algal density, use of organic manure) and salinity (discontinuous pumping) fluctuate creating an unstable environment. This, together with the fact that population cycles are yearly interrupted seems to favor oviparous reproduction.
Integrated systems in which Artemia culture (high salinity) is combined with the culture of shrimp or fish (stocked in the ponds with lower salinity) also exist. As for the small salt works, brine shrimp culture usually depends on the availability of high saline water and is often limited to certain periods of the year. Management of these ponds is similar to the management of the Artemia ponds in artisanal salt farms.
Intensive Artemia culture in ponds can also be set up separately from salt production. Ponds are filled with effluent of fish/shrimp hatcheries and/or grow-out ponds. As salinity in these systems are often too low to exclude predators (45 to 60 g.l-1), intake water is screened, using filter bags or cross-flow sieves. Agricultural waste products (e.g. rice bran) and chicken manure can be used as supplemental feeds. Systems can be continuous (at regular intervals small amounts of nauplii are added to the culture ponds) or discontinuous (cultures are stopped every two weeks).