Annual Changes in the Nitrogen Compound Ratios between Urine and Plasma in Carp Cyprinus carpio

In the plasma of carp, no statistically significant annual variation was observed in the concentrations of protein, creatine, ammonium, creatinine, and uric acid except for urea. The concentration of protein remained relatively constant throughout the year. Annual variation patterns of U/P ratios of nitrogen compounds were similar to the corresponding urinary ones. The U/P ratio of protein was always low, less than 0.05, while that of ammonium exceeded 16.6. That of urea varied from 0.1 to 8.7 according to season. Those of creatine, creatinine, and uric acid were more than 1.0 and annual variations were large. These results suggest that carp kidney possibly plays some essential role in the homeostasis of these compounds in the blood.