Calcium and Other Ions in Blood and Skeleton of Nicaraguan Fresh-Water Shark

Science  21 Sep 1962:
Vol. 137, Issue 3534, pp. 984-986
DOI: 10.1126/science.137.3534.984-a


The bull shark, Carcharhinus leucas, employing archaic but effective means of regulating the physical-chemical composition of its body fluids, thrives in tropical fresh-water rivers and lakes. The ionic strength of the serum and the concentrations of total solutes, calcium, urea, and other ions are below the levels found in marine elasmobranchs but higher than the levels in teleosts. The patterns of the calcium deposits of the vertebrae are identical in marine and fresh-water subspecies.