INDICATOR BACTERIA AND LIMNOLOGICAL PARAMETERS IN FISH PONDS

The populations of indicator bacteria (mesophilic, coliform and fecal streptococci) together with relevant limnological parameters (temperat ure, oxygen, BOD and chlorophyll-a) were recorded during a 6 year stud y of three eutrophic ponds. Ecosystems were manipulated with fish (Cyp rinus carpio) in 2-year management cycles: in spring of the first year , the pond was stocked with young fish, and in the fall of the second year it was drained and mature fish were harvested. Fish management ha d a direct influence on bacterial numbers and on the basic parameters of the systems. A statistical analysis using t-tests found significant differences in oxygen concentration, chlorophyll-a and BOD during bot h years of fish management. A water temperature model was calculated o n an extensive homogenous data set (197 measurements), by fitting a re gression curve. During each season, populations of indicator bacteria increased with increasing water temperature, and maximal numbers of ba cteria were recorded during the summer months. Correlation analysis (f itted Spearman correlation coefficient) confirmed that temperature had a positive significant effect on population dynamics. The results dem onstrate that fish stocking can affect bacterial population, in the se nse that during high fish biomass (second years) the numbers of indica tor bacteria as well as BOD and phytoplankton were higher. If pond wat er quality must be optimised for the purposes of drinking or recreatio n, the planned fish yield may have to be reduced.