With new practices of less water exchange and maintaining water quality with probiotics, Soc Trang farmer Anh Tai says he achieves higher survival rates at target harvest sizes, if he adheres to the pond carrying capacity
In conversations on the performance of the shrimp industry in Vietnam, industry players will give a regional picture of success rates of crop cycles, based on the pond system. In the central and northern region where more of the earthen ponds have HDPE liners, it ranges from 70-80% whereas in the southern region, namely in the Mekong Delta, it has been as low as 15% attributed to farming in unlined earthen ponds.
Additionally, in the south, the poor quality of shared water resources is a very serious concern. This raises the cost of water treatment which now comprises 10% of the cost of production. Success rate is taken as the percentage of crops with good margins. Another woe is the extremely high costs of production as compared to Vietnam’s major competitors in the global shrimp market, namely India. In Vietnam the average cost of producing 20~25g shrimp is USD4.00/kg.
Soc Trang and Bạc Liêu in the Mekong Delta are the leading shrimp farming provinces, which produced 200,000 tonnes of vannamei shrimp in 2022. Feed company, Uni President Vietnam (UPV)’s technical team, based in Soc Trang, recently said that the success rate in Soc Trang has gone down to around 25%. Three years before, success rates were much better. Water salinity in the Mekong Delta ranges from 5 to 15ppt and at the lower salinity, farmers face soft shell shrimp. A popular yet costly practice over the last few years is to exchange pond water frequently. Today, an accepted practice is treating water in reservoir ponds, exchanging water as little as possible and using more pond probiotics.
Over the last few years, most of the leading shrimp feed millers in Vietnam have been developing culture models for their farmer clients. They have tackled water quality as the route against disease outbreaks and for more predictable harvests, thus improving success rates for their clients. These systems were on display at the recent VietShrimp 2023 (see pages 5-6).
Control biomass and water exchange
One example is farmer Anh Tai in Soc Trang, who was exchanging water at 30-40% daily and now is only topping water at 30% over 3-4 days. He applies chlorine to his two water treatment ponds. He also follows protocols on water quality management with probiotics as suggested by UPV which have been selecting farmers facing challenges and grooming them to be successful. In Soc Trang, the strong team of Vu Trong Huy and Nguyen Van Minh Tuyen, two field technical managers, has been nurturing Tai to reach his target production of 50g shrimp at a much lower cost of production. “Here in Soc Trang, many farmers face issues with water quality. With the poor water quality in the
Mekong Delta, intake water must go through four levels of water treatment. Despite this, Vibrio levels remain high and so we have proposed the use of water probiotics. Even though the probiotic dosage used is higher, in the end it is more cost effective for the farmer. Ultimately, the target is to reduce Vibrio loads and outbreaks of Enterocytozoon hepatopenaeid (EHP) and white faeces syndrome (WFS),” said Huy, technical advisor at the R&D Centre in Soc Trang.
UPV has been encouraging farmers to follow its pond and water management protocols. “Since 2022, we have conducted seminars weekly; in 300 demonstration ponds (3-4 ponds of 1,000m2 to 1,500m2 we have achieved 80% success rates. Of course, it was difficult during the pandemic period. Farmers reported many disease outbreaks, the most serious was WFS where the final result was slow growth. Other diseases are early mortality syndrome (EMS) or acute hepatopancreatic necrosis disease (AHPND) and EHP. In the background is white spot syndrome virus (WSSV),” said Huy.
The model that UPV has been proposing to shrimp farmers in Soc Trang is stocking PL8 at 1,300 -1,500 PL/m2 in nursery ponds over 30 days to reach 1g. The stocking density in grow-out ponds is 200-220 PL/m2.
UPV Director Wu Sheng Wei who is the major force in this development of the UPV model, said, “Using the nursery phase and with our technical support, farmers can overcome the disease challenge during the first 30 days of culture (DOC), and look ahead to a higher survival rate. We have set ‘8 Protect Lines’ to guide farmers on how to increase their success rates. These include feed nutrition, sludge removal, feed management, biomass control, water disinfection, probiotic bacteria system, health products and confidence.”
Tai started shrimp farming, initially with the black tiger shrimp, when he was only 21 years. Today, at 34 years Tai has four ponds at his farm in Soc Trang in the Mekong Delta. “Disease is my worst nightmare. When I exchanged water, it not only was time consuming, but the survival rate was only 50%. Today with this new practice, I can achieve 90% survival rate. I remove the sludge three times daily and the protein scum four times daily. I keep the dissolved oxygen level at 7 mg/L.” Today, Tai is an exemplary farmer for UPV.
A model with many phases
In Vietnam, the three main pond models are earthen ponds, lined earthen ponds and round tanks. Wei Che Wen, Asia Sales Manager said that UPV is suggesting two carrying capacity limits per tonne of water. “Depending on the pond system design, we specify from 2 to 2.2kg/tonne water for round tank systems and lined earthen ponds, and one kg/tonne water for earthen ponds. In round tanks and lined earthen ponds, the stocking density is 200 PL/m2. Partial harvesting is essential to achieve these carrying capacities. In final harvests the total production capacity can be 5kg shrimp per tonne of water. Our strategy is also to bring down the cost of production of 20-25g shrimp to under USD3.5/kg.
In the case of Tai, his pond now fits into the lined earthen pond model since they were lined with 0.5mm HPDE liners a year ago. His culture starts with a shaded nursery pond of 1,000m2 stocking 1,000/m2 post larvae (PL8) which come from the nearby Viet Uc hatchery. The nursery phase is over 30 days until shrimp reach 1g. Tai added, “I use as nursery feed, UPV’s starter feed TOPONE, the premium grade feed with 45% crude protein.” According to Wei, it is usual for farmers in the Mekong Delta to use this premium feed for the first DOC 40. Tai himself is convinced that using this feed helps him secure a steady crop. “I have achieved a feed conversion ratio (FCR) of 1.25 for a harvest size 43g with this feed,” he said.
In the grow-out phase, Tai uses two 1,000m2 ponds and transfers shrimp interchangeably as he fulfils the pond carrying capacity of 2kg/tonne of water. Ponds are aligned in a row, close to each other so that transfer is a quick process. Initially, 1g post larvae from the nursery pond are transferred into two parts of the first grow-out pond, one at a stocking density of 350 PL/m2 and the other stocking at 175/m2. Shrimp from the pond portion with higher density are then moved to another pond to match the stocking density of 175 PL/m2.
Tai continues to spread out his shrimp over the three ponds as they grow. Such a practice is not unique to Tai’s ponds but is a common practice all over Vietnam. What is unique here is using the premium feed to achieve 50g vannamei shrimp over a culture period of 4 months and 4 days.
According to Tai, “So far, for this season (stocking early December 2022), he has had two partial harvests which started when the crop reached size 55/kg (18g) at DOC70. The volume was around 2 tonnes and next was another harvest of 4.5 tonnes of size 35/kg (28.6g) shrimp at DOC 105. The third harvest is 1.5 tonnes of size 25/kg (40g) at DOC 134 and the final harvest at DOC 142 for size 23/kg (43.5g) at 3.5 tonnes. After each partial harvest, Tai moves the shrimp in his three ponds to balance back the carrying capacity.
R&D on the best water treatment and farming protocols
In general, shrimp culture is in earthen ponds and only 20% are in round tanks. The trend to line ponds with HDPE liner is catching up; in 2023, it was estimated that in Vietnam, only 30% of earthen ponds are lined and most of them are in the central region. The deterrent is the cost of liners. Nevertheless, when conducting research into developing management strategies at its R&D centre, UPV is taking into consideration the needs of all these three farmer groups, i.e., those operating earthen and lined ponds and round tanks.
In Vietnam, genetics-wise, the preference is for fast growth and robustness, with the balanced line genetics proposed by three broodstock suppliers – Shrimp Improvement Systems (SIS), Kona and SyAqua. Charoen Pokphand has the turbo range of fast growth shrimp. “Farmers focus on fast growth of 30g shrimp in DOC 100. Working with feed conversion ratios, we calculate the feeding rate for each scenario and each farm. The average FCR is 1.4 but we work with farmers who strive for better success to achieve an FCR of at least 1.2~1.3. We want them to bring down their cost of production to under USD3.5/kg for size 50/kg shrimp. Considering partial harvesting we can also push for the harvest capacity to be at 5kg/tonne of water,” said Wei.
The round tank production model is the central feature at the R&D centre in Soc Trang. UPV collaborated with Canadian startup, Wittaya Aqua on an innovative water treatment technology for the nursery and grow-out tanks. Each round tank for grow-out or nursery is associated with two treatment tanks for water settlement and treatment. “During the grow-out cycle, we exchange water every 4 days at 30% and for the nursery cycle we exchange water every 5 days at 20%. After each cycle, wastewater is channelled out if the water is not used for recycling. These practices depend on the ammonia, nitrate and nitrite levels in the water. There are six round tanks for grow-out and two for nursery culture,” said Wei. “Our round tanks are 500 tonnes in capacity. However, in some farms, the capacities range from 800-1,000 tonnes.
“Ultimately, the aim at this centre is to develop the appropriate technology to increase productivity and reduce cost of production and bring up the success rate in Vietnam’s shrimp farming,” concluded Wei.
The article was published in issue May/June 2023
