Estradiol-17β and nutritional status affect calcium balance, scale and bone resorption, and bone formation in rainbow trout, Oncorhynchus mykiss

Abstract

The effects of estradiol-17β (E2) on bone resorption and formation as well as its effects on scale resorption were investigated in rainbow trout in order to elucidate the role of the hormone in calcium mobilization from calcified tissues, and to clarify the importance of scale and bone as calcium reserves during sexual maturation. Furthermore, the effects of nutritional status on calcified tissues and E2-induced calcium mobilization were studied. In fed as well as fasted rainbow trout, E2 treatment increased scale osteoclastic activity measured as tartrate-resistant acid phosphatase activity, and reduced scale calcium content, suggesting that E2 increases scale resorption in both the fed and fasted fish. Using histomorphometry, E2 treatment was found to decrease pharyngeal bone resorption in fed, but not in fasted rainbow trout. The E2 effect on rainbow trout bone is consistent with its physiological role in mammals and birds where E2 has been reported to decrease bone resorption. It appears therefore that rainbow trout protect their skeleton and instead use scales as a source of calcium during E2-induced calcium mobilization. The formation of pharyngeal bone was decreased by fasting, and the importance of the nutritional status for the activity of the bone cells in rainbow trout is therefore emphasized.