Use of Strontium as a Nutritional Marker for Farm-Reared Brook Trout

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Abstract
Strontium was tested as a nontoxic and inexpensive internal marker in fish. Six groups of brook trout (Salvelinus fontinalis), 20-23 cm long, were fed a commercial feed enriched with strontium (Sr + +) over periods of 4 and 6 weeks. Calcium and magnesium levels remained stable, but the concentration of Sr + + increased in the newly formed portions of opercular bones. One of the diets (200 μg Sr + +/g feed, dry weight) resulted in an average concentration of 1,800 μg Sr + +/g dry weight of opercular bone after 6 weeks. This was significantly different from that measured in wild brook trout (270-445 μg/g) but comparable to concentrations found in wild brook trout raised in seawater as well as in several other saltwater species. The flesh of groups fed 200 and 400 μg Sr + +/g feed contained a level of strontium comparable to that of brook trout raised in seawater and five times that of the brook trout in the control group. Strontium appears to be a good marker for brook trout farm-raised for market....