Comparison of two methods for distinguishing wild from hatchery-reared salmon (Salmo salarLinnaeus, 1758) in the Baltic Sea

A discriminant function based on scale characters was used for distinguishing wild and hatchery-reared Baltic salmon. The function was based on the following three variables: the width of the first freshwater annual zone; the maximum number of circuli per year in the freshwater zone; and the mean distance between circuli in the freshwater zone. Using this function, it was possible to correctly classify 92.63% of fish of known origin. Use of the so-called visual method resulted in a 100% correct classification of the same sample. When the two methods were compared using a scale sample of unknown origin, the results showed that the two methods classified 219 and 257 fish the same. The suitability of the methods for stock identification and the discrepancies between them are discussed.