Abstract
Freshwater catfish, Heteropneustes fossilis, were injected daily intraperitoneally either with vehicle (0.1 ml of 0.6% NaCl/100 g body wt) or calcitonin (0.5 MRC U/100 g body wt) and maintained either in artificial freshwater, calcium‐rich freshwater, or calcium‐deficient freshwater for 10 days. The blood samples were collected on days 1, 3, 5, and 10 after initiation of the experiment, and serum calcium and inorganic phosphate levels were analysed.
(i) Artificial freshwater: There is no change in the serum calcium and inorganic phosphate levels of calcitonin‐injected fish.
(ii) Calcium‐rich freshwater: In vehicle‐injected fish there is a progressive hypercalcemia from day 1 to day 5. On day 10 the value decreases but it is still hypercalcemic. No change has been noticed in the serum calcium level of calcitonin‐treated fish. In vehicle‐treated fish the serum inorganic phosphate level indicates a decrease on day 10. The serum inorganic phosphate level of calcitonin‐treated specimens exhibits no change.
(iii) Calcium‐deficient freshwater: There is a progressive decrease from day 1 to day 3 in serum calcium level of vehicle‐injected fish. Thereafter, from day 5 the level increases thus resulting in hypercalcemia on day 10. Calcitonin treatment to the fish evokes a decrease in the serum calcium level from day 1 to day 3. Thereafter a significant hypercalcemia is recorded on day 5 and day 10. In vehicle‐injected fish the serum inorganic phosphate levels decrease from day 3 to day 5. However, the value increases on day 10. Serum inorganic phosphate level of calcitonin‐treated fish exhibits a decrease on day 1. Thereafter, it rises progressively from day 3 to day 10. © 1993 Wiley‐Liss, Inc.