Raising sea crabs and mantis shrimp in plastic boxes using recirculating technology is gaining traction among local farmers. This method minimizes environmental dependency, reduces waste, and offers high value.
In the rural area of Long Khánh Commune, Duyên Hải District, Trà Vinh, Trần Minh Nhật, 29 years old, has been engaged in crab fishing. With a passion for agriculture, four years ago, Nhật searched online for YouTube videos that demonstrated how to raise crabs in plastic boxes using circulating technology from abroad. This technology allows crabs to thrive independent of their living environment. The water system is treated, and its quality remains stable, leading to a low mortality rate for the crabs.
Recognizing the potential of this approach, in 2022, Nhật invested in 50 breeding boxes along with a recirculating system featuring coarse filtration tanks, microbial filtration, and UV light for water treatment, costing around 15 million VND. He also purchased 50 juvenile crabs at a cost of 3 – 5 million VND, releasing them into individual boxes.
Initially, without experience in selecting juvenile crabs and managing the recirculating system, Nhật faced failures due to high crab mortality. Undeterred, he learned from online resources and participated in local training courses for crab farming. Nhật adjusted environmental parameters, maintaining natural salinity, a pH of 7.5 – 8.5, and regularly supplementing microbes, while adding water weekly since the farming area is near a river.
Trần Minh Nhật and vacuum-packed soft-shell crab products raised using recirculating systems, showcased in Trà Vinh province at the end of 2023. (Photo: NVCC).
When selecting juvenile crabs, Nhật took great care to find reputable suppliers, choosing crabs that were firm and free from injuries. After several failures, he refined his techniques, resulting in more stable crab growth.
To date, Nhật has expanded his model to 1,000 breeding boxes, investing in additional equipment for fresh oxygen aeration and foam separation, with a total cost of 300 million VND. With a larger scale of farming, he now harvests 180 – 200 kg of soft-shell and green crabs monthly, earning a profit of 20 – 30 million VND.
After over four years of raising crabs in boxes, Nhật estimates that investing in 1,000 breeding boxes will recoup capital within about 1 to 1.5 years. Sharing his successful crab farming experience, Nhật states that 60% of success relies on the quality of the stock, while the remaining 40% is about operating the recirculating system. “Farmers in this model need a certain level of knowledge and understanding of technology to adjust water parameters appropriately, ensuring crab growth“, Nhật emphasizes, believing that the box crab farming model has great potential for economic development. Residents can cultivate in any area without relying on proximity to the sea. Currently, Nhật is guiding three other local farmers to invest in technology and techniques for raising 300 – 500 boxes each. He guarantees the market for their crabs.
Also utilizing recirculating technology, Master Lê Ngọc Hạnh, from the Aquaculture Research Institute 2, is experimenting with raising mantis shrimp in plastic boxes on a larger scale of over 1,000 boxes in Bà Rịa City, Bà Rịa – Vũng Tàu Province.
According to Master Hạnh, the recirculating system for raising mantis shrimp is fundamentally similar to that of raising crabs. However, due to crabs’ unique ability to live both underwater and on land, the oxygen aeration system operates for a shorter duration compared to that for shrimp. Conversely, mantis shrimp require a continuously operating recirculating system to stabilize their environment. They swim constantly underwater, leaving less waste and reducing care labor. The growing period for mantis shrimp is approximately 3 – 6 months, reaching market weight. The largest mantis shrimp size is around 3 – 6 shrimp per kg, priced at about 1.2 – 1.5 million VND.
Master Hạnh notes that with a rearing cost of around 700,000 VND per kg, farmers can earn a profit of 500,000 – 800,000 VND. With over 1,000 boxes, after one cycle of up to a year, they could break even on the investment costs for machinery and equipment.
On selecting stock, experts from the Aquaculture Research Institute 2 indicate that crabs and mantis shrimp are often weakened and die due to environmental shock. Therefore, when selecting crab juveniles, farmers should look for suppliers with a stable salinity environment. The harvesting and transportation methods should avoid causing injuries or stress to the animals.
For mantis shrimp, it is advisable not to select individuals that are too small, as this will prolong the rearing time; it’s better to choose those that are 10 – 12 shrimp per kg. Farmers should also avoid selecting those that have just molted, as they are very weak and prone to death. During transportation, it is essential to provide sufficient oxygen and to place them in an intermediate environment similar to that of their breeding boxes to help them acclimate, reducing mortality from environmental shock. “It is crucial to thoroughly understand the harvesting and transportation processes of the supplier. Farmers should require suppliers to follow these procedures to ensure the stock is healthy,” Master Hạnh advises.
A model for raising sea crabs in plastic boxes at the High-Tech Agricultural Zone in Ho Chi Minh City. (Photo: Hà An).
According to Dr. Nguyễn Thị Kim Liên, Head of Aquaculture Technology Support Department at the High-Tech Agriculture Business Incubator Center (Ho Chi Minh City), the recirculating system fundamentally includes filtration devices to separate waste, biological filtration systems, oxygen supply devices, and UV light for water sterilization. However, depending on the farming conditions, the filtration system may vary. In coastal areas with natural water sources, periodic replacement of 50% of the water can help farmers reduce some filtration systems, thereby cutting costs. She emphasizes that during farming, controlling toxic gases in the water such as NH3 and NO2 is crucial through daily rapid testing. If the concentration of toxic gases is too high, it can cause environmental shock leading to crab deaths.
In addition to crabs and mantis shrimp, Recirculating Aquaculture Systems (RAS) can also be used to raise mud crabs, sea cucumbers, and various freshwater species such as soft-shell turtles and blue river prawns… The RAS technology has been researched and applied in several countries, including Israel, the Netherlands, and China, for nearly 30 years. In Vietnam, this technology has been adopted by many farmers for over a decade due to the rich supply of materials and more competitive prices.
Experts indicate that the cost of each RAS system depends on the type of materials used and the investment in water filtration systems. As these systems are installed indoors, the equipment lasts 5 – 10 years or more. Given the high initial investment, RAS is suitable for high-value, short-term aquaculture. This technology helps save water, control all input factors, breeding conditions, and waste discharge. Consequently, the cultivation environment is designed to minimize or eliminate the need for antibiotics and medications. RAS technology has been recommended by international organizations such as FAO and Eurofish as a sustainable aquaculture method.
The recirculating water system helps farmers control the environment when raising seafood in boxes. (Photo: Hà An).
Associate Professor Dr. Nguyễn Hữu Dũng, President of the Vietnam Marine Aquaculture Association, evaluates that using recirculating systems for aquaculture allows farmers to monitor the growth of each individual in the boxes, ensuring environmental factors, leading to significantly lower mortality rates compared to traditional farming. According to Mr. Dũng, this model can be widely replicated, aiding economic development for local residents. Specifically for soft-shell crabs, he mentions that the domestic market as well as markets in Singapore, South Korea, Taiwan, and China are highly favorable. However, he expresses concern that as the number of farmers increases, it may lead to a shortage of quality stock, disrupting the value chain. He also suggests that for crabs and other high-value aquatic species, the government should collaborate with businesses to establish processing systems and food products from local resources to enhance value for domestic consumption and export.
