Introduction
Fishponds are essential ecosystems inhabited by many different species and serving commercial and non-commercial functions. Therefore, the management of fishponds can be a crucial factor affecting all the organisms inhabiting a given pond, as well as the physicochemical parameters of the pond water.
In this study, we investigated the effects of traditional (business as usual, BAU) and adjusted fishpond management (natural production, NP; natural production with supplementary feeding, NPF) on biota diversity and its seasonal development (macrozoobenthos, zooplankton and phytoplankton), the development of physicochemical water parameters, and the food source preferences and movement ecology of common carp.
Materials and Methods
To evaluate the impact of above-mentioned management strategies, four ponds were monitored monthly throughout the vegetation season over a period of three years (2021–2023). At each sampling point, the entire biota of the fishpond (fish, macrozoobenthos, zooplankton and phytoplankton) was sampled. In addition, physicochemical water parameters were monitored over the same period. To reveal the movement ecology of common carp, acoustic telemetry was employed. Additionally, stable isotopes and a fatty acid approach were employed to reveal the common carp’s feeding preferences. The management of fish stocks was based on the natural production of the given ponds and the level of supplementary feeding planned.
Results
Biotic communities: Fishpond management significantly impacted the seasonal development of the macrozoobenthos, zooplankton, and phytoplankton communities. Macrozoobenthos communities were the most sensitive to differences among BAU, NP and NPF, while zooplankton and phytoplankton communities were less sensitive.
Water physicochemical parameters: Fishpond management had a significant impact on the physicochemical parameters of the water. In addition, the seasonal development differed between BAU, NP and NPF management. The most important of parameters affected by pond management were dissolved inorganic nitrogen, chlorophyll a, and total phosphorus.
Common carp food source preferences: The preferred food sources changed over the season, regardless of the type of pond management. In NP management, common carp simply follow the most abundant food source. Nevertheless, when supplementary feeding was applied, the common carp utilized it at a higher rate, regardless of the abundance and biomass of other potential food sources.
Common carp movement ecology: The activity and spatial use of carp changed over time, influenced by temperature, food availability, and stocking density. Their activity peaked in spring and early summer, with the highest levels occurring at night and dusk. During warmer months, the fish favored shallow areas (less than 0.5 meters deep), probably due to thermoregulation, oxygen levels or access to prey. Variability in the use of foraging sites and food composition among individuals correlated with growth, highlighting the importance of behavioral traits in resource acquisition.
Discussions
This study highlights the complex interactions between fishery management practices and the aquatic communities of Central and Eastern European carp ponds. The management of fishponds is a key factor influencing the communities that inhabit them, as well as the physicochemical parameters of the water, the movement ecology of common carp and their food source preferences.
While the ponds may appear similar, the combination of environmental and human-induced factors has caused them to evolve in slightly different ways. Fish stocking based on the pond’s natural production and proper supplementary feeding (here calculated to achieve a net production of 220 kg/ha of carp from additional feeding) does not negatively affect the communities and temporal trends of zooplankton and macrozoobenthos.
Acknowledgment: The study was funded by NAZV QK21010131 (PI: Lukáš Veselý).