Pond cascades as a tool for ecological aquaculture allowing natural zooplankton succession, nutrient retention, and multiple stocking-harvesting cycles

Fishpond cascades represent interconnected artificial ecosystems with multifaceted ecological and economic potential. This study investigated the fishpond cascade integrated into an agricultural landscape in South Bohemia (Czechia), employed for advanced fry production without any manuring and feeding. Four inter-connected fishponds (area 1-3 ha, 1 m mean depth, batch release-refilling of water) were studied over one growing season. Results demonstrated effective nutrient recycling and removal through the cascade, showcasing its self-purification ability. Both total phosphorus and total nitrogen concentrations in the last pond of the cascade averaged at 55 % and 61 % of those in the first pond, respectively. Zooplankton communities displayed seasonal succession patterns with the dominance of microcrustaceans (mainly Daphnia spp.), influencing the early diets of predatory fish. The multiple stocking-multiple harvesting strategy (MSMH) was employed to maximize fish production. Albeit naturally low survival rates (3-16 %) of advanced fish fry in ponds, the ecological and economic benefits of MSMH in the pond cascade system were evident. The study indicated that pond cascade systems can be environment-friendly and economically efficient for advanced fry production, contributing to landscape sustainability, water quality, and cultural heritage. The study encourages, where appropriate local conditions allow, the establishment of pond cascade systems as an ecological engineering concept bridging aquaculture and sustainable landscape development, as well as contributing to bioremediation and other ecosystem services.