Fishery management shapes limnological dynamics in hypereutrophic fishpond ecosystems

Decades of intensive carp aquaculture, along with agricultural and municipal nutrient inputs, have driven many central European fishponds into a hypereutrophic state, while their responses to different management strategies remain insufficiently understood. We studied four hypereutrophic fishponds in Czechia over 4 years (2021–2024) under contrasting fishery management regimes: traditional business as usual (BAU) with high fish stocking and reduced supplementary feeding, and those adjusted regimes with reduced stocking aligned to fishpond carrying capacity, winter drying, and either the presence (SF+) or absence (SF−) of cereal supplementary feeding. The adjusted management showed greater seasonal variability in nutrient ratios and phytoplankton biomass, while BAU exhibited uniform seasonal patterns. Supplementary feeding under adjusted fish stock did not increase total nutrient concentrations, suggesting that the feeding alters nutrient pathways rather than exacerbates eutrophication. Nutrient stoichiometry (DIN:TP) and chlorophyll a were the main drivers of management effects. These results indicate that even chronically hypereutrophic fishponds remain responsive to fishery management. Aligning fish stocking with natural production, combined with winter drying and controlled feeding, can ameliorate limnological functioning without reducing fish yields, offering a pathway toward more sustainable carp aquaculture.