This question is constantly stirring public and professional discussions among ecologists and fish farmers, as well as the broad public that often blames the fish farmers from deteriorating the water quality associated with the massive development of algae and cyanobacteria. A team of scientists from the FFPW USB, while monitoring the performance and production parameters (e.g., survival, growth, carp production per unit of pond area) of common carp stocks with different genetic productivity potential, also evaluated the effect of these stocks on water quality parameters (e.g., total phosphorus, inorganic nitrogen, COD, BOD5). The study was conducted under the commercial conditions of a fish farm from the yolk-sac fry stage throughout the three growing seasons. The scientists obtained data on fish performance, production parameters and water quality at the outlet from 32 fishponds. Water quality at the tributaries was also monitored in 20 fishponds.
Until now, no similarly focused and extensive study that, among other things, aimed to answer the above question could be found in the scientific literature. No significant effects of the carp stock size on the water quality in fishponds was observed in this study. The data obtained also indicate that under certain conditions, water quality parameters does not fundamentally change even at the carp stock size of 1200 kg / ha of fishpond water surface area, which is a double the Czech average.
The results of the presented study also support some previous findings concerning the dynamics of water quality in fishponds in connection with the nutrient load of the pond basins. The water quality parameters improved in fishponds with nutrient-rich tributaries, and on the contrary deteriorated in fishponds with nutrient-poorer tributaries, regardless of carp production size in fishponds. Therefore, it seems that the above-mentioned water quality parameters in fishponds are not related to carp farming, but to the overall nutrient load of the fishpond basins resulting from natural and other anthropogenic factors acting in the area.
More detailed information can be found in the original scientific article:
Kocour, M., Prchal, M., Lipka, J., Valentová, O., Kroupová, H.K., 2025. Effect of common carp group, mass yield and supplemental feeding on basic water quality parameters under semi-intensive pond management in Central Europe: Implications for selective breeding under near-natural conditions. Aquaculture, 742168.
