Breeding fish and tomatoes together

When fish farming fall as waste products exactly the nutrients that need tomatoes to grow. Scientists have now developed a system in which they breed fish and tomatoes together in one plant. This creates an almost closed cycle that requires extremely little water and is very environmentally friendly.

A rich harvest at the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB): the scientists were able to bring in almost 600 kilograms of tomatoes, and they were able to multiply their edible fish by 150 kilograms. With this, their idea of ​​a combined fish and tomato cultivation has proven to be practicable. The so-called aquaponics system opens up new possibilities for sustainable protein and vegetable production in dry areas.

Fish regularly need purified water because their excretions are converted into harmful substances in the water. In nature, plants essentially take on this cleaning function because they use the waste products of the fish as nutrients. Following this example from nature, the IGB scientists have developed a greenhouse in which they grow fish and tomatoes under one roof: After mechanical and biological filtering, the wastewater from fish farming is fed to the plants, which are then completely supplied with nutrients. The roots of the plants are washed directly by the nutrient-rich water, they do not need any soil. Specially developed valves allow the tomatoes to use minimal water. The cleaned water is then returned to the aquarium as fresh water. Dr. Bernhard Rennert from the IGB explains: "This cycle enables emission-free fish and vegetable farming, which is only fed with fish feed and an extremely small amount of water."

To ensure that the aquaponic system is as closed as possible, the scientists have integrated a great deal of technology: cold traps catch the transpiration water of the tomato plants from the air, which is then returned to the fish tank. A heat pump ensures a constant temperature throughout the year - cooling in summer and heating in winter. The electricity for the entire system comes from a photovoltaic system on the roof.

The tomatoes were planted in May, the fish seedlings were also grown in August and the aquaponic system has been running in a cycle ever since. While the scientists are further optimizing the system in the test facility at the IGB, there are already plans to build a similar facility in Spain. The new approach offers advantages for this location in particular, because in addition to the low water consumption, the system is very environmentally friendly in contrast to the vegetable production that is currently widespread there.

Bernhard Rennert made the first attempts in this direction in the GDR as early as the 1980s. But the goal of environmental compatibility was not considered relevant by the donors at the time and the research work came to a standstill. Today, however, the ecological benefit is seen - but the economic benefit can also play an important role for arid regions.

Source: Berlin [IGB]