Fishpond management and ecological stability of fishponds -as a key water habitats of the Třeboň region

Fishponds have an important role in the hydrological system of the Třeboň region and generally they represent the most common type of stagnant water habitat in the Czech Republic. Most of the fishponds are several hundred years old, and have therefore lost most of their man-made character. The period of intensification of fish production started in the 1930s, when liming and fertilization of the fishponds became a common practice. Since the 1930s, fish production has increased from a mean of about 50 kg ha-1 to more than 500 kg ha-1. Common carp, Cyprinus carpio L. has been the main cultivated fish species. Management for higher fish stock densities, accompanied by higher nutrient loads result in increasing trophic levels, ultimately reaching a state of 'hypertrophy'. The main symptoms of this state are the massive development of phytoplankton and cyanobacterial ' algal blooms', great fluctuations in oxygen concentrations, pH, which, in turn, destabilise the fish pond ecosystem