New analysis finds that extensive systems aquaculture systems with a nature-based approach perform 36% better than intensive ones when taking into consideration external factors such as environmental, social, and economic impacts.

This analysis was undertaken by the IISD Nature-based Infrastructure Global Resource Center, using its Sustainable Asset Valuation (SAVi) methodology, in collaboration with GIZ and the Shamba Centre for Food & Climate. As part of the analysis, it assessed the performance of four aquaculture systems in Madagascar.

The research question

In Madagascar, 80% of the population lives inland with limited access to protein and nutrient-rich foods, leading to undernourishment and malnutrition in rural areas. Traditionally, inland fish production have relied on intensive or semi-intensive aquaculture methods. However, an alternative aquaculture approach – extensive rice-fish system -  could be transformative in Madagascar by providing the population with a steady supply of fresh fish and additional revenue streams.

Rice-fish systems enable carp and tilapia to be farmed alongside rice production in paddy fields and provides symbiotic benefits for both species: the rice provides fish with a sheltered habitat and insects to feed on, while the rice is fertilized by the fish waste. Local rice farmers can make additional revenue by farming fish as well as rice and improve their animal-sourced protein consumption.

However, how does this method of aquaculture compare with other aquaculture systems? To answer this question, researchers compared and assessed the performance of four aquaculture systems:

• Extensive rice-fish farming: land-based aquacultural system using earthen ponds to cultivate fish symbiotically with rice, optimizing nutrient exchange to balance natural feed use and promote mutual growth.

• Semi-intensive fish farming: This method in earthen ponds utilizes its natural productivity, in combination with supplementary feeding to achieve higher productivity.

• Intensive net cage fish farming: Fish farming in large bodies of water, relies on feeding caged fish with formulated feeds.​

• Intensive fish farming in tanks: This aquaculture system relies on fish tanks using recirculating aquaculture systems and feeding fish with formulated feeds.

The assessment modelled the economic, social and environmental costs and benefits of these four aquaculture systems over a 25-year lifecycle, from 2025 to 2050. Using quantitative modelling informed by qualitative methods, such as system mapping, the assessment examined the interactions among variables such as water and nutrient dynamics, fish and rice production to analyze both the sustainability and profitability of the different approaches.

And the results….

The assessment found that extensive rice-fish farming demonstrates high environmental performance with minimal water usage, efficient nutrient utilization, and a reduction in green house gas (GHG) emissions of -0.81 kg-CO2e/kg rice. By introducing fish into a rice paddy reduces methane emissions by increasing soil oxygenation, thereby limiting the conditions favourable to methane-producing bacteria. It also contributes to biodiversity, supporting diverse aquatic and terrestrial species, fostering ecological balance, habitat diversity, and conservation efforts.

In contrast, intensive systems, such as net cage and tank farming, exhibit higher environmental impacts, including GHG emissions, significant water demands, and up to 14 times greater water pollution due to nutrient export.

While intensive systems are financially attractive given the scale of operations, they underperform economically due to high external costs. Extensive systems, characterized by a higher labour-to-capital cost structure, not only support substantial employment and community development but also show strong viability from societal and financial perspectives. For rural communities, extensive rice-fish farming enhances nutritional diversity and food security while also fostering rural employment and economic stability.

To read the full report: Sustainable Asset Valuation (SAVi) of Aquaculture in Madagascar: An integrated assessment of aquaculture systems beyond production