According to Laval University in Canada, not only could used water from fish farming stimulate tomato growth, but it could also protect them against certain pathogenic fungi.
The researchers measured the reaction of tomatoes grown in greenhouses watered twice a week with used water from a rainbow trout farm. The trout farm was also located on campus.
Tests showed that thanks to this water rich in nutritious elements, leaf surface area, root biomass and plant heights increased by 31%, 19% and 6% respectively. Moreover, microorganisms that pollute these used waters seemed to fight certain pathogenic fungi that attack tomatoes. Growth of P. ultimum and F. oxysporum fungi diminished by 100% and 32% respectively during in vitro tests. Grant Vandenberg says that the increase in tomato growth and decrease in fungi means that “it is a very interesting way to value waste and deal with environmental problems that hold back fish farming development in Quebec.”
A well made fish farming system would have a small ecosystem, where the water, nutrients and carbon dioxide go from the farming basin into the greenhouse, rather than being thrown back into nature. “We could integrate fish and vegetable productions under one roof, or install them in adjacent buildings” explains the researcher. In a closed circuit system, the water is recycled and it is therefore interesting to heat it. Fish growth is twice as fast when the water is at 15 degrees rather than 5 degrees Celsius.