Studies on fish urine. III Annual changes in the osmolarity and inorganic ion level ratios between urine and plasma in carp Cyprinus carpio.

The blood properties of free swimming carp were examined as a function of annual changes in urine properties. Statistically significant changes were found in Ht values and concentrations of K+ in the plasma. Throughout the examination period, U/P ratios with values below 1.0 were observed in osmolarity (minimum 0.06-maximum 0.19) and inorganic ions (Na+, 0.05-0.20; K+, 0.10-0.86; Ca2+, 0.03-0.19 and Mg2+, 0.02-0.60). Individual differences and annual changes in most of the blood properties were not particularly remarkable compared to those found in urine. The changing patterns of U/P ratios were close to those of the concentrations of urine components.