Some success stories overcome EMS in Vietnam
How some shrimp farms in Vietnam are overcoming the EMS in Vietnam.
This year, it will be two years since early mortality syndrome/acute hepatopancreatic necrosis (EMS/AHPNS) was first reported in shrimp farms in Vietnam. It started in the Mekong Delta in farms culturing mainly the black tiger shrimp Penaeus monodon which contributed more than 60% of shrimp production in the country. EMS gradually spread to many farms all over the entire country, bringing fear among farmers in the country. Today, farmers are putting all their efforts to overcome EMS.
Shrimp with hepatopancreas destroyed
Recently, I had the opportunity to visit many farms along the coastline of Vietnam from Cam Ranh to Ho Chi Minh City. Usually, during March, over 50% of ponds in the shrimp farming areas would have been stocked. This was not the case this year as most ponds are still empty and about 30% were still in the preparatory stage. Since 2011, the provincial fishery officials have instructed that farmers stock after April, to avoid EMS. Most farmers will follow but others have given up hope. They no longer have sufficient funds to restock their ponds after experiencing several crop losses. I compared this situation with the initiatives in Thailand. While in Thailand, we have launched a campaign on post larvae quality, the same is not being considered by the Vietnamese government.
During my trip, I talked to some farmers who have managed to continue farming and are harvesting shrimp of good sizes such as at size 40/kg. This was in spite of stocking during the critical periods such as during December 2012. l have estimated that now among 100 farmers, only 3 – 5 farmers have actually managed to farm shrimp continuously without any losses from EMS. Following a visit to five farms recently, I have discussed and obtained some ideas on how they have managed to overcome EMS. In general, their practices are quite similar to that of Thailand. They focus on post larvae quality, feed management and aeration.
Post larvae quality
Usually it is not easy to select post larvae but the successful farmers have the same advantage; they either have their own hatchery or a reliable source of quality post larvae. Farmer Toan, has his own hatchery. He will continue to rear post larvae up to PL20 to stock his own ponds. During this time, he uses the best quality feed such as Artemia with enrichment diets. In contrast, Vinh has a close relationship with a hatchery owner and is able to select a good batch by tracking the growth history in the hatchery. Another three farmers have their own ways to secure good quality post larvae.
Successful farmers, from left, Khoa, Phi and Kha
Nursing to post larvae
With the exception of Toan, all the four other farmers have their own nursing unit, most of them nurse post larvae at a density of around 1,500 – 2,000 PL/m2 for the first stage in a nursing unit. When shrimp is bigger at size 500/kg or based on water quality, they will transfer shrimp to a pond. Again, when the shrimp reach size of 200/kg or when the water quality deteriorates, shrimp are transferred again to another pond. This continues until shrimp reaches size 100/kg, when they start partial harvesting to reduce the biomass and hence prevent the pond from exceeding the carrying capacity.
How do they judge when to transfer or start partial harvesting? All five farmers have different ways. Sometimes this is based on water color, dissolved oxygen concentration or average daily growth (ADG). The key factor is management on demand with careful monitoring.
Feed management and pond additives
The other common link among all five farmers is feed management. All follow strictly feeding on demand protocols. They adjust the amount of feed according to weather conditions, shrimp behavior, environment, water color and temperature. The use of pond additives is common in Vietnam’s shrimp farming industry. However, today the farmers use them carefully. They now follow the right dosage, time and usage instructions. This raised the production cost to almost USD 4/kg. “The culture has absolutely changed. We have to do our best and understand that a high investment cost for the right product which really works is actually cheaper than a low cost investment on products with unknown performance results.” said a farmer.
Previously, although products carry on how to use them effectively, few farmers follow them. Some of these instructions are for the following products: Iodine must be stored away from light; vitamin C should be added quickly and also used as fast as possible; microorganisms need a balance of C:N ratio and alkalinity of over 80 ppm; chlorination must be applied at low pH and insecticide must be used under higher pH.
The right dosage has always been neglected by the farmers because they never take into consideration the pond size to calculate the exact water volume. Often, there is a worry of costs and farmers merely want to under-dose to save costs. Most farmers are not aware that they need to take into consideration many parameters (such as organic matter content in the water, pH, alkalinity, salinity, water transparency) before they use a product in their culture system. Only the successful farmers actually pay full attention to these details. Attention to aeration is another change which we see in the successful farms.
Among the 21 farms visited, there were 2 farms facing problems. Although they are careful with PL selection, they overstocked in the first nursing pond, up to 3,000 PL/m2. This is a mistake because the farmer plans to transfer the shrimp to grow-out ponds when shrimp size is 3g at around 35 days of culture (DOC). The total biomass at maximum size in this pond can be up to 10 kg/m2, this is too high to load even at a maximum carrying capacity. Generally carrying capacity in the commercial pond should not be more than 2,5 kg/tonne of water.
Another farmer stocked 500 PL/m2 but is using the same aeration protocol as in a normal grow out pond with only 12 HP. He also expects to transfer shrimp at 40 DOC when the shrimp weight average around 4g and his pond area is 5,000 m2. When extrapolated, this means a total stocking of 2.5 million PL. When shrimp reach size about 4g the total biomass will be 10 tonnes! Since one HP can support 400kg of shrimp biomass, this pond aeration system should accept only a biomass of 5 tonnes only. Here the limiting factor is aeration.
Farmers May (left) and Vinh
In conclusion, we can see that the working techniques to avoid EMS in Vietnam are as follows:
- A strict implementation of post larvae selection, i.e. to select only high quality post larvae and reject all sub-standard quality post larvae
- Nurse post larvae before stocking with enrichment diets
- Apply feed on demand management
- Supply high levels of aeration
- Use only quality products with right dosage, techniques and time.
- Carrying capacity, i.e. stock below carrying capacity, the optimum carrying capacity should be around 1.5 kg biomass of shrimp/m3
Farmer Toan (middle) is all smiles.
For the moment, these guidelines should be used. It is also important to be open, to learn and share with each other.
By Soraphat Panakorn/AQUA CULTURE Asia Pacific – May/June 2013