RAS technology brings climate-resilient mud crab farming to the Mekong Delta coast

Mangrove root systems and associated microbial communities perform natural water treatment functions (nutrient uptake, organic matter decomposition, and pathogen attenuation) that complement RAS. By reducing the volume of nutrient-rich effluent discharged from crab culture, RAS reduces the organic loading pressure on mangroves and tidal flats.

The RAS model does not replace the ecosystem services that mangroves provide — it reduces the pressure on them, creating space for coastal habitats to recover and regenerate.

This integrated model represents the hybrid NbS as the heart of the TCCF-Coastal Squeeze project approach. Sustainable aquaculture and mangrove conservation are framed not as competing land uses but as mutually reinforcing components of a coherent livelihood and resilience strategy for coastal communities.

How RAS Works: Engineering a closed loop

RAS is a water treatment and reuse technology that continuously processes pond water through a series of mechanical and biological filtration stages before returning it to culture units thereby eliminating or dramatically reducing the need for external water exchange.

RAS deployed under this project have three core treatment stages. Drum filters remove suspended solids and organic particulate matter through mechanical screening. Protein skimmers eliminate dissolved organic compounds to improve water quality. Biological filtration units house nitrifying bacterial communities that convert toxic ammonia (NH₃) into nitrite (NO₂⁻) and then into the less harmful nitrate (NO₃⁻). Together, these three stages maintain stable water chemistry and reduce pathogen load without the need for water exchange.

By eliminating routine water exchange, the RAS model severs the direct pathway through which pathogens and poor-quality canal water enter the culture environment — the single greatest source of disease risk in coastal mud crab farming.

IUCN technical team and Vinh Xanh Company install an RAS unit at a household site in Ca Mau Province © IUCN Viet Nam

A further design feature distinguishes RAS from communal pond culture: individual compartments. Each crab is housed in a separate rearing unit, eliminating cannibalism, a major source of mortality in high-density mud crab culture, and allowing farmers to monitor individual growth, adjust feeding, and identify health issues before they escalate.

The compartmentalised structure also offers a commercial advantage: farmers can hold animals at market weight and release them selectively when price conditions are favourable, rather than accepting prevailing prices at the end of a fixed fattening cycle. In a market characterised by seasonal price volatility, this flexibility can meaningfully improve profits per cycle.

Installation, technology transfer, and capacity building

On 27-30 May 2026, a team from IUCN and Vinh Xanh Company installed six RAS units in three locations: Vinh Hau and Long Dien Communes in Ca Mau Province, and Cu Lao Dung Commune in Can Tho City. Working directly with households, the team assembled and pressure-tested each system, verified hydraulic connectivity between treatment stages, and ran initial start-up cycles to confirm system stability before handover.

Installation was immediately followed by a 1-day hands-on technology transfer session for participating farmers. The training was designed around operational competency: farmers worked with the equipment directly, learning to operate and adjust each system component while trainers guided them through normal operating conditions and common fault scenarios.

The training covered the operating principles of the three filtration stages; interpretation of water quality test results for pH, total alkalinity, total hardness, and NH₃ concentration; recognition of early warning indicators and the corresponding corrective actions; and routine maintenance procedures including filter cleaning cycles, media inspection, and pump maintenance.

Water quality monitoring was focused. Participants conducted hands-on test kit reading during the session and read results against target parameters for mud crab culture. The ability to monitor and respond to water chemistry independently was identified as a core competency for sustainable system operation at the household level.

Trainer guides households through hands-on water quality testing, demonstrating the use of test kits to measure pH, alkalinity, hardness, and ammonia levels © IUCN Viet Nam

The installation in May 2026 represents the first full deployment cycle of RAS technology under the project. IUCN and Vinh Xanh Company will provide ongoing technical support to households, monitor system performance and water quality parameters, and document production outcomes including crab survival rates, growth performance, and fattening cycle economics.

Lessons learned from this pilot including system design adaptation for smallholder conditions, training methodology, and the integration of RAS with mangrove management will inform the development of scalable, replicable livelihood models for coastal communities in the Mekong Delta. The project shows that technology-enabled aquaculture intensification and coastal ecosystem conservation are not only compatible but can be mutually reinforcing pathways toward long-term community resilience in the coastal landscape.