Seasonal dynamics of primary and secondary production in carp ponds

The aim of this study was to evaluate the interdependency between seasonal successions of phytoplankton, zooplankton and macrozoobenthos community structure in carp ponds. The main objectives were to examine shifts in dominant species (or groups), changes in size structure and biomass dynamics of these aquatic communities as key groups dominating in carp ponds. The study was conducted in three earthen fish ponds at the experimental fish farm of the Faculty of Agriculture, University of Belgrade (Serbia). Values of physical and chemical environmental parameters were similar between ponds, with exclusion of electroconductivity and transparency. Zooplankton was dominated only by one small bodied Cladocera Bosmina longirostris, dominating usually in ponds with planktivorous (and bottom feeding) fish. In the case of investigated ponds stocked with common carp yearling having low density (and biomass) of macrozoobenthos, probably the supplemental feed was the main source of nutrients for the fish. Nevertheless, the size structure of zooplankton in this study was also shaping the algal biomass primarily by grazing pressure. As a result, a high production of inedible algae occurred in ponds, probably not only as a result of low competition for nutrients with other algae, but also by favorable environmental conditions, as very high water temperatures and a vast amount of nutrients present in ponds. Macrozoobenthos organisms were in the early phase of inhabiting the ponds substrata, thereby having low densities and biomass. Knowing that three type of supplementary feed, were applied to ponds, the obtained results concerning fish are logical. However, in pond D3 fish were fed with row cereals (wheat, maize and barley) the lowest fish mass was obtained, the highest Cyanophyta domination and algal bloom occurred, as well as the lowest zooplankton biomass production. Pond L2 had extruded pellets as supplemental feed, presuming to be the best utilized by fish. During the first two months of the study period, a mistake concerning feed calculation for L2, resulted in a amount of uneaten feed in the pond, probably causing a lower weigh gain in fish. Consequently, pond L3 had the highest weight gain in fish and highest zooplankton production. Finally, it can be concluded that aquatic communities are influenced by a complex of physical, chemical environmental factors as well as by strong interdependencies. In the present study a significant negative correlation between crustacean biomass and chlorophyll a in pond D3 suggests that there was a high control of phytoplankton production, mainly Cyanophyta, on zooplankton biomass, indicating a more prevailing bottom-up than top-down process.