Temperature and Mass-Dependence of N and P Excretion By Common Carp: Contribution to Lake Nutrient Budgets

We used the metabolic theory of ecology (MTE) to determine scaling of metabolic nutrient excretion rates by common carp (Cyprinus carpio) with body size and temperature. At high biomasses, common carp have negative impacts on water quality, and one mechanism is excretion of the nutrients N and P, but this has rarely been put in the context of other nutrient sources. We measured whole-body and mass-specific excretion rates during summer and winter for carp of different sizes (28−1,196 g) to produce an allometric scaling model capable of predicting excretion at different temperatures.  We found positive relationships between both dissolved and total nutrient concentrations and fish wet mass in summer and winter, with greater excretion rates in summer (mean water temperature 24^oC) than in winter (mean water temperature 9^oC). Mass-specific excretion rates decreased with increasing fish size, consistent with the MTE, and the temperature-adjusted model explained more variation for N excretion than for P.  The proportion of dissolved nutrients (NH₄ and PO₄) to total nutrients increased with increasing fish size. We used lake models to estimate the significance of fish excretion to lake nutrient dynamics, and determined that carp can contribute significant amounts of N and P to the lake ecosystem.