Original paper

The effects of size and density of carp (Cyprinus carpio L.) on water quality in an experimental pond

Driver, P.D. Closs


A field experiment was used to quantify the effects of carp (Cyprinus carpio) biomass density and size-structure on dissolved oxygen, conductivity, turbidity, pH, temperature, nutrient concentrations and algal biomass in replicated enclosures. The treatments in this field experiment comprised different combinations of large (2 kg) and small (0.7 kg) carp, and low (330 kg/ha), intermediate (570 kg/ha) and high (650 kg/ha) biomass densities. The impacts of carp were more size-dependent than described in previous studies. In particular, carp size was more important than carp biomass density in determining the concentration of total phosphorus and algal biomass. On the other hand, a more even mix of carp sizes increased total nitrogen. These results were compared to other studies of carp impacts. Although carp size tends to be poorly and inconsistently reported, and focused on small carp if mechanisms of nutrient mobilization are tested, there is evidence that differences in carp size explain some of the conflicting results among carp studies. We argue that there is a continuum of effects where larger carp tend to mobilise phosphorus through sediment suspension and smaller carp tend to mobilise phosphorus through excretion. Additionally, we suggest that there is little evidence for a carp size effect on nitrogen among various studies, regeneration of nitrogen by carp is mostly from excretion and, consequently nitrogen regeneration is likely to be proportional to the biomass of carp.


nutrient releaseexcretionnitrogenphosphorussediment suspension