Germany: Tilapia fish and tomato; a sustainable combination?

Tomatoes and fish are being farmed together in the same environment. Dirty water from the fish tanks is used for providing mineral nutrients that are essential for plant growth. The fish are very hungry. When Hendrik Monsees - a biologist at the Institute of Freshwater Ecology and Inland Fisheries in Berlin - throws dry food into the aquarium, the tilapia (a type of fish) immediately swim to the surface to snap it up. They fight for the food. Water is sprayed out of the chest-high aquarium. Monsees ducks for cover. "When tilapia are hungry, there's a lot of spray," he says with a smile.

A few hundred tilapia are held in a dozen fish tanks at the institute. They are kept in a greenhouse where numerous tomato plants are grown. Air-conditioning keeps the temperature of the greenhouse constant at 27 degrees Celsius (81 degrees Fahrenheit) - making the environment conducive for tomatoes and tilapia. The aim of the project is to grow vegetables and farm fish in zero emission conditions.

Food production in a highly technical environment

Tomatoes and fish thrive in an artificial environment that uses technology to ensure optimal results. The fish are kept humanely, says Werner Kloas who also happens to be the founder of the greenhouse. The tanks do not contain more fish than are normally found in their natural habitat - no more than a school of fish. And the tomatoes grow in an artificially enhanced environment. Instead of soil, they are planted in mineral wool.

Picture courtesy DW/Thomas Gith

"The cultivation of plants without soil is called hydroponics" Monsees explains. He moves a few leaves to one side and points to the small tomatoes. Growing tilapia and the vegetables has been successful as the researchers have demonstrated several times in the greenhouse.

This type of cultivation and farming is nothing new. Vegetables are grown in greenhouses around the world. And farming fish in tanks is nothing revolutionary. What is new is that water from the fish tanks is being used to grow the tomatoes. Aquaculture, the farming of aquatic organisms, and hydroponics - growing plants using mineral nutrient solutions in water, without soil - have been separate domains, Kloas explains.

Essentially, this project combines aquaculture and hydroponics. "When the plants need water and the nutrients, it is delivered from the fish tanks," Kloas says.

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