Potential pathways for interaction between fish and cyanobacteria include fish grazing directly on
cyanobacteria, fish preying on grazers of cyanobacteria, fish supplying nutrients through excretion, fish
providing nutrients by resuspending sediments, and fish altering the availability of nutrients and light by
damaging macrophytes. The dominant interactions in Australia are likely to be through pathways that
increase the availability of nutrients at the bottom of the food web. Carp probably contribute to these
pathways more than do other species by excreting nutrients, resuspending sediments and damaging
macrophytes. Further research, on both alien and native fish species, is needed to quantify these
processes. Grazing of cyanobacteria by fish is probably trivial because freshwater fish in Australia lack
mechanisms to process cyanobacterial cells effectively. Trophic interactions between planktivorous
fish, zooplankton and cyanobacteria require closer study to assess the potential for preventing
cyanobacterial blooms by manipulating natural predator communities in Australia. However, the need
to protect and strengthen native fish stocks precludes removal of native fish to reduce predation
pressure on zooplankton communities. Alternative solutions that combine control of nutrients entering
waterways and removal of carp have a higher likelihood of success.
The hidden role of multi‐trophic interactions in driving diversity–productivity relationships
