Intensive cage farming
Cage farming is a traditional form of pangasius production. While it was still common to use cages up to the early 2000s, it nearly collapsed due to a combination of factors when the pangasius boom started. As cage farming depends on good water quality and favourable water currents it was mostly practised in the upper Mekong River, in the provinces close to the Cambodian border. Cage farming declined quickly after 2004 and nowadays cage production contributes less than 1% to the total pangasius production. In the provinces An Giang and Dong Thap cage farming is still practised, and some individual household use this type of production to sell to the domestic market.
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Type of farmers
Individual households still use this practice for their own subsistence or to target the domestic market. Farm sizes are small as the cages are put in existing waterways.
Production and harvesting system
The cages are usually made of floating wooden frames containing several cages which vary from a size of 3x5x3m (small) to 5x10x4m (medium) or bigger. Cages are either floating on the surface and reach to a maximum depth depending on the cage size, or are submerged in the river at depths around 5m. Natural currents take care of continuous water exchange. Commercially oriented cage farming of pangasius is practiced in monoculture.
Pangasius is harvested periodically throughout the year. Harvest is carried out by harvesting the entire cage at once. Average grow-out time is 7 months, with a range of 4 to 10 months depending on the stocking season, fingerling size, feed quality and harvesting weight. This allows for an average of 1.7 production cycles per year. Most farmers harvest at a size of 800 to 1,000 grams depending on demand. With a yield of roughly 35%, this results in two filets of 140 to 180 grams. For specific markets the harvest weights can reach 1,200 grams resulting in fillets of 220 grams.
Stocking densities and productivity
Cages are typically stocked with fry at 100-150 pcs/m3. Average productivity is typically 100-120 kg/m3/crop. In comparison with ponds, cages allow higher fish densities and have a higher productivity. Nevertheless, fish survival rate in cages is lower than in ponds, as cages depend very much on water quality. The lower survival rate is one of the reasons why farming shifted from cage to mainly pond farming.
Use of seed, feed and other inputs
Fingerlings come exclusively from approved hatcheries. Pangasius breeding is strongly regulated and driven by governmental support. The Vietnamese government operates the most important research centre for pangasius fry, Research Institute for Aquaculture (RIA), which also produces a significant part of the available pangasius fry. Many privately operated hatcheries exist as well, most of which are located in the provinces Dong Thap and An Giang. Pangasius fingerlings are often placed in nurseries before being stocked in cages. There are a number of specialist nurseries operating in the different provinces. They buy fry from RIA or private hatcheries and raise it to different sizes of fingerlings. For cage production larger fingerlings are preferred as this increases the survival rate.
All commercial operating producers use pelleted feed from approved feed mills. There are many big fish feed companies that produce feed for pangasius with specific formulas depending on the respective fish size. Chemicals are not used as a rule. It might be that some non-certified producers use chemicals such as additives or antibiotics. Home-made feeds bare the risk of containing substances that are not allowed by Vietnamese law.
Pangasius is stocked in cages periodically throughout the year with peak stocking times from March to July. This is because hatcheries generally close down during the cold months from November to January as broodstock does not spawn during that time, and therefore fry and fingerlings are not available. Although fish can be harvested all year round. Peak harvest takes place between October a d February.