by Niels O.G. Jørgensen(The Royal Veterinary and Agricultural University)
Microorganisms are important organisms in the regulation of potential environmental effects of fish ponds. Through the activity of microorganisms, released organic matter from fish and undigested food pellets are mineralised to inorganic nutrients that may stimulate the algal growth. Production of organic matter during an enhanced algal growth can cause anoxia, and killing of fish and other aquatic organisms. An additional effect of nutrient release from fish ponds may be a stimulation of toxic, photosynthetic cyanobacteria (“blue-green algae”). The cyanobacterial toxin microcystin is lethal to cattle drinking stream water with a dense cyanobacterial population. Furthermore, transport of microcystin to groundwater reservoirs, as has been observed in some European countries, may lead to human health problems. Other cyanobacteria produce the off-odour geosmin, which penetrates the fish and reduce their quality and commercial value.
The application of copper as an algicide and substance against ectoparasite infection in fish ponds introduces another environmental risk, as copper in higher concentrations is toxic and growth-reducing, e.g., to microbes. Also, copper is suspected to change microbial communities, which may explain the stimulation of geosmin-producing bacteria and moulds after addition of copper.
In the present research proposal we address the following environmental issues related to freshwater aquaculture:
- Occurrence and degradation of microcystins and geosmines will be measured in aquacultures with a variable fish production to establish possible relations between abundance of fish and concentrations of microcystines and geosmines.
- Environmental consequences of copper addition will be analyzed by relating the amount of bio-available copper, measured with a new biosensor, to the total amount of copper in water, sediments and in sludge from the ponds. In addition, the effect of copper on nutrient cycling, bacterial activity and diversity of microorganisms will be investigated.