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FEEDING BOTH POND AND FISH: A PATHWAY TO ECOLOGICAL INTENSIFICATION OF AQUACULTURE SYSTEMS

The nutritious pond concept is a novel approach that enables the pond itself to contribute significantly to the diet of the farmed fish/shrimp. Our research shows that feeding the pond by balancing the carbon-to-nitrogen ratio can increase the contribution of naturally occurring food in the diets of the cultured animals, thus enhancing reliance and reducing production costs and environmental impact. Field trials are currently being conducted in Vietnam and Bangladesh to better understand nutrient transfer in aquaculture ponds. The results of these trials will inform the development of products for fish farmers that have high potential for scaling to other developing countries.

Introduction

Aquaculture is one of the fastest growing food production sectors in the world and now provides more than 50% of the fish and shellfish consumed globally. This growth is predicted to continue in the coming years. However, the sector is highly dependent on agricultural crops and wild fish for feed as well as freshwater and land resources for inland aquaculture. At the same time, scientists and policy analysts have raised concerns about the environmental impact of such growth and the need to steer the sector toward more resilient and sustainable production.

As aquaculture has expanded and intensified, so has its dependence on natural resources. Future growth will depend on the sector’s ability to overcome this dependence, and  Credit: Olivier Joffreincrease feed supply while mitigating environmental impact. Research  on  the  impact  of  aquaculture  on  surface  water  quality and greenhouse gas emissions shows that aquaculture is lagging behind livestock and agriculture. This is despite significant improvements in recent decades in aquaculture system efficiency through, for example, the reduction and replacement of fish meal and fish oil in diets. At present, however, feeding systems target the cultured animals with little attention paid to the possible contribution of the pond ecosystem and its food web to the animals’ diet.

What is a nutritious pond?

In a typical aquaculture production system, the food web (i.e. the food chain within the pond, from phytoplankton, microbes and other organisms through to the fish or shrimp cultured in the pond) is stimulated by uneaten and undigested feed, which essentially acts as an expensive fertiliser in the pond.

This fertiliser is not designed to be efficient for the pond ecosystem, as its nutritional composition is aimed at fish or shellfish and not the other pond organisms. This creates imbalances in the system and in the nutrient cycles. The recycling of animal waste becomes suboptimal, making the pond  environment  unhealthy  and  vulnerable  to  disease. In  general,  farmers  around  the  world,  and  especially  in developing countries, use a variety of probiotics, prebiotics and other additives to mitigate these imbalances, increasing the production cost without necessarily achieving the desired outcomes.

One solution is a system that feeds both the pond and the cultured animals, limiting imbalances in the nutrient cycles by producing wastes that are easily decomposed. As a result, mineralisation is fast, the production of natural foods for the animals is optimal, waste accumulation is minimised and the pond environment stays clean and healthy. This is the idea behind the nutritious pond concept, which aims to harness the  potential  of  a  largely  untapped  resource:  increasing the harvest of pond nutrients via the food web and turning waste into food for the animals. It is an approach that could, in theory, be scaled to a large number of semi-intensive production systems as it is estimated that more than 60% of all finfish and shrimp comes from these systems. Such an approach would support the intensification of aquaculture while minimising environmental impacts.

How are we developing the concept into a product?

The nutritious pond project is a five-year research initiative funded by the Netherlands Organization for Scientific Research (NWO)  and  the  WorldFish-led  CGIAR  Research  Program on Fish Agri-Food Systems. It involves a multi-stakeholder approach to embed fundamental and applied research along with product design to adapt the new feeding system to the local technological, social and institutional context.

This array of research, which is providing deep insight into pond  ecology  and  nutrient  transfer,  is  shared  with  and discussed by different stakeholders involved in the innovation platform to design new protocols for on-farm trials. Platform members  defined  their  requirements  and  expected performance to evaluate the trials. Since the beginning of the project in 2016, four different formulations combining pelleted feed and different types of carbohydrate (molasses, cornstarch, a mix of rice bran and cassava, or cassava on its own) have been tested in semi-intensive shrimp ponds in Vietnam. In Bangladesh, on-farm testing was performed on GIFT, and the nutritious pond feed was designed as a single pellet with a higher carbohydrate content.

Source: Joffre O. and M. Verdegem. 2019. Feeding both pond and fish: A pathway to ecological intensification of aquaculture systems. INFOFISH International 3. https://www.worldfishcenter.org/content/feeding-both-pond-and-fish-pathway-ecological-intensification-aquaculture-systems.

 

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