The demand for protection of natural resources has stimulated the development of environmental friendly aquaculture technologies. Freshwater pond fish farming is a unique segment of European aquaculture. Pond fish farms besides producing fish provide ecosystem services, contribute to achieve the goals of NATURA 2000, a network of nature protection areas in the territory of the European Union. Extensive fish ponds are usually surrounded by reed belts and natural vegetation, thus providing important habitats for flora and fauna. Many pond fish farms have been turned into multifunctional fish farms, where various other services are provided for recreation, maintenance of biodiversity and improved water management.
The technology on combined intensive-extensive pond systems for water-efficient fish production offers a solution for the treatment of nutrient-rich effluents of intensive pond aquaculture systems. The objective is to reduce pollution from intensive systems and utilize the waste organic content of the effluent water for additional fish meat production, thus increasing the production efficiency and reusing the water. First pilot system established in Hungary in 1998.
The principle of the method is to treat the effluent water enriched with organic and inorganic nutrient of intensive fishponds (high stocking density, intensive feeding) in an extensive pond (medium stocking density supplementary feeding). In the extensive pond, a part of the nutrients is utilised through various biological production processes and the other part is fixed in the pond sediment, and the water treated or purified is recycled to the intensive fishponds. Filtering and bottom-feeding herbivorous and omnivorous fish are reared in polyculture in the extensive pond. The nutrient retention capacity of the system allows for an efficient treatment of the water, after which it is returned to the intensive ponds, ensuring water-efficient fish production.
This solution reuses the waste nutrients, which would otherwise be lost, results in a 20-25% improvement in nutrient utilization. The combined fish production resulted in higher protein utilisation by 26%. The system proved itself efficient in reducing water pollution while obtaining additional fish yield in a water-efficient way.
By using the solution, both the water demand of fish production and the nutrients loading in the environment are decreased.
The system can be adapted to existing or newly built pond systems. Its efficiency is limited by the nutrient retention capacity of the extensive pond but, in case of using carp-based polyculture, 1 ha of pond area can efficiently treat the water from the intensive production of about 10 t fish in Hungarian conditions. Higher treatment efficiency may be expected in warmer climates.
The solution was thoroughly researched in order to better understand the nutrient flows in the system, thus allowing to fine-tune the system and enhance its efficiency. This scientific knowledge and know-how can be of use to other countries.
Budget: The investment and operating costs are about 2.5 and 1.25-2.25 EUR/kg fish yield, respectively. However, it depends on the local material and labour costs, as the system is based on ordinary fish ponds, the investment costs are basically the same as those of pond construction, i.e. they depend on the availability of water, the costs of labour etc. If the system is developed on the basis of an already existing pond system, it significantly reduces the investment need. The operating costs are also similar to the typical local operating costs of pond systems, although the system uses less water, feed and manure than comparable conventional systems while providing extra fish production.
National Agricultural Research and Innovation Center, Research Institute for Fisheries and Aquaculture (NARIC HAKI)
Contact person: Dr. Dénes Gál, Research Institute for Fisheries and Aquaculture (NARIC HAKI)