TARTRATE-RESISTANT ACID-PHOSPHATASE AS A MASKER FOR SCALE RESORPTION IN RAINBOW-TROUT, ONCORHYNCHUS-MYKISS - EFFECTS OF ESTRADIOL-17-BETA TREATMENT AND REFEEDING

In teleosts, a considerable part of the body calcium is found in the s cales. Associated with the scales are osteoblasts and osteoclasts, and during periods of high calcium demand such as during sexual maturatio n or starvation, the scales can be resorbed and thereby act as an inte rnal calcium reservoir. In mammalian bone tissue, the activity of an a cid phosphatase (ACP) isoenzyme, tartrate resistant acid phosphatase ( TRACP), can be used as a marker for osteoclastic activity. In the pres ent study, an evaluation of TRACP as a marker for osteoclastic activit y in teleost scales has been performed. ACP and TRACP was histological ly localized at resorption sites around the edge of the scales as well as at resorption holes in the scales. The optimal conditions for bioc hemical measurements of ACP and TRACP activity were found to be pH 5.3 , 10 mM paranitrophenylphosphate, incubated for 30 min at room tempera ture, and 10 mM tartrate added when required. Using TRACP as a marker, estradiol-17 beta (E(2)) was found to increase the proportion of scal es being resorbed, as well as the number and size of resorption sites per scale. Also, the scales of E(2)-treated fish showed weaker stainin g for calcium. Together, the obtained data indicate that estradiol-17 beta induces osteoclastic activity in teleost scales, resulting in inc reased resorption of the scales. A period of refeeding following a per iod of starvation did not have detectable effects on the scale osteocl astic activity and scale resorption.