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Calcium and calcitonin studies in Pacific salmon, genus Oncorhynchus, and rainbow trout, Salmo gairdneri Watts, Eric George

Abstract

In mammals, calcium homeostasis is under the control of parathyroid hormone and calcitonin. Fish lack parathyroid glands but large amounts of calcitonin are located in the ultimobranchial gland. The objective of this thesis was to examine calcium metabolism and the possible physiological role of calcitonin in rainbow trout, Salmo gairdneri, and Pacific salmon, genus Oncorhynchus. Ultimobranchial gland calcitonin concentrations were measured in trout and salmon under a variety of conditions, using the rat bioassay. Assays indicated that calcitonin concentrations in the ultimobranchial glands varied widely and showed no consistent relationship to plasma calcium and phosphate levels, sex, sexual maturation, environmental calcium concentration or species. The ultimobranchial gland calcitonin concentrations of fingerling trout (age 7-8 months) were lower than adult trout, suggesting a possible relationship between calcitonin and growth. The biological half-life of salmon calcitonin was measured in free-swimming cannulated trout and salmon. Results indicate that the half-life of salmon calcitonin in fish (trout 27.6 min., salmon 48.0 min.) is considerably longer than that found in mammals. The effect of salmon calcitonin on plasma calcium and phosphate was examined in trout and salmon. Salmon calcitonin injection did not cause hypocalcaemia or hypophosphatemia in fingerling trout and was also ineffective in cannulated adult trout. No significant change in plasma electrolytes or urinary electrolyte excretion was observed following infusion of salmon calcitonin into cannulated adult female salmon,, A migration study on the Chilko race of sockeye salmon was carried out to investigate plasma electrolyte and tissue changes as these fish migrate from sea to fresh water. Ionic and total serum calcium were determined and results indicate that the sockeye maintain a relatively constant serum ionic calcium level throughout their spawning migration, indicating effective homeostatic control. Measurements using a sensitive and specific radioimmunoassay, revealed that calcitonin can be detected in the plasma of salmon and that this hormone was continuously secreted under basal conditions. The levels of calcitonin detected in salmon plasma were higher than those found in most mammals. A sex difference in plasma calcitonin levels (females higher than males) was found in sockeye, as well as in the coho and chindok adult salmon. This sex difference appears to be unique to salmonids. Female plasma calcitonin levels were found to rise during the migration and to decrease following spawning« Plasma calcitonin changes Followed a different pattern in the migrating male sockeye. The plasma calcitonin changes were clearly not related to plasma calcium and phosphate alterations. In the female sockeye, calcitonin appears to be involved in sexual maturation and spawning. Removal of the gonads from mature female sockeye resulted in a marked drop in circulating plasma calcitonin levels. Estrogen injection into these gonadectomized salmon dramatically elevated plasma calcium but did not restore the plasma calcitonin levels. These investigations indicate that the physiological role of calcitonin in calcium metabolism in fish may be different from that in mammals.

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