Earth Ponds for Fish Farming

If you were considering investing in a fish farm how likely are you to opt for using earth ponds?  To answer this question we need to consider the benefits and limitations of earth ponds as a suitable infrastructure for fish farming.
 
Earth ponds are constructed by removing topsoil and then digging down into the clay-rich subsoil to create a basin.  The clay-rich soil that is dug out of the depression is used to build walls around the pond, which are well compacted to ensure they are watertight.  A drain is fitted to the lowest point of the pond to drain the water as required via an automatic overflow or removal of a pipe to facilitate complete drainage of the pond for the harvesting of the fish.  The sight of shoals of fish gently swimming around in a pond reminds one of nature, which is exactly what earth ponds replicate, with the addition of well managed inputs from the farmer.
 
The first advantage is that earth ponds are far cheaper to construct per unit volume of water than either tanks or cages, which are the alternative infrastructure choices, and this construction can be done by hand without machinery if you have access to inexpensive labour.  However, the counterbalance to this is that earth ponds can only be stocked at low densities, so the cost of the infrastructure relative to output tonnages may not be as economical as initially envisaged.
 
Each species of fish thrives under a specific set of environmental parameters, of which water temperature is a key component.  If the earth ponds are constructed in a tropical climate for the farming of a warm water fish species, then the fish should grow well throughout the year, enabling the farmer to have year-round production and sales.  However, if the farm is based in a cool temperate climate and the farmer is rearing warm water fish, then the growth of the fish will be reduced for part of the year, resulting in less production from the ponds and more complicated marketing to maintain market share and secure regular income across the seasons.  Earth ponds are therefore best suited to climates that do not have significant seasonal temperature fluctuations.
 
The construction of an earth pond requires a high proportion of clay in the soil in order for the ponds to seal and hold water.  Also as mentioned, fish are stocked at low densities in earth ponds, thus requiring large areas of land that have a high clay content, and the slope is not too steep in order for the ponds to be constructed cost effectively.  A final physical consideration is that ponds require large quantities of water to replace evaporation and seepage, and for the draining and filling of the ponds associated with the fish management cycles.  Thus, only a limited number of potential fish farming sites are suitable for the farming of fish in earth ponds.
 
The typical cycle for the management of earth ponds for tilapia is to fill the pond with water and add fertiliser to develop the natural food chain in the pond in the form of algae and various invertebrates.  After 2 weeks the pond is stocked with fingerlings at a moderate density of 20 fish/m2.  After 8 weeks the pond is harvested, the fish sorted and restocked into other ponds that have been prepared as above at 3 fish/m2, and left to grow for a further 3-4 months, whereafter they are harvested and sold.  During harvesting the pond is emptied, limed to sterilise the surface mud and left for 10 days to dry and crack, whereafter the cycle commences again with the filling and fertilising of the pond.  The fish are fed a medium quality pellet twice daily, and a portion of the water is replaced weekly throughout the growth period.
 
Due to the low density at which fish are stocked the risk associated with earth pond fish farming is low.  Production output can be significantly increased (doubled!) from the same infrastructure via the inclusion of an aeration system.  But aeration requires a backup power supply to ensure continuous oxygen supply to the elevated fish densities.
 
In summary, earth ponds are low risk and fairly inexpensive infrastructure which are very suitable for the farming of fish under the correct climatic conditions.  If you have such conditions, and the necessary physical parameters required to construct earth ponds, then this is an excellent infrastructure choice for fish farming.