Differentiation of Freshwater versus Saltwater Striped Bass by Elemental Scale Analysis

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Abstract
The differences in concentration of 10 elements in scales of striped bass Morone saxatilis from several freshwater (< 0.1.permill.), estuarine (0.5-15.permill.), and saltwater habitats (20-30.permill.) in the eastern United States were evaluated. Barium, iron, aluminum, calcium, magnesium, manganese, potassium, sodium, strontium, and zinc were measured by flame atomic absorption spectrophotometry. Absorbance values for barium, iron, and aluminum were extremely erratic due to matrix interferences. Discriminant function analysis correctly classified 95% of freshwater and 95% of saltwater fish based on Ca and Mg alone. These two elements were the single best indicator pair. When seven elements were considered, 97 and 95% of fish from fresh water and salt water, respectively, were classified correctly. One-way analysis of variance of individual elemental contents of scales from different salinities consistently distinguished among freshwater, estuarine, and saltwater fish, although not always in a predictable order. Concentration of elements varied with sex, but, when all data were combined, only manganese concentration was significantly affected by sex. Fish size was often negatively correlated with elemental content. The strongest correlations were between magnesium and fork length, weight, and age in all three environments. We concluded that discriminant function analysis, in conjunction with age and growth information for individual striped bass, can provide a useful means for distinguishing between freshwater and saltwater striped bass.