The use of fatty acid markers to distinguish hatchery and wild chum salmon fry and a description of post-stocking changes in fatty acid levels

Fatty acid compositions of chum salmon ( Oncorhynchus keta ) fry were examined to distinguish between hatchery and wild fish in natural environments. Levels (%) of 18:2n-6 (linoleic acid) were significantly higher in fry obtained from a hatchery (13.0 %) than in wild fry collected in a river (2.1 %). Conversely, levels of 20:5n-3 (eicosapentaenoic acid; EPA) were significantly lower in the former (4.2 %) than in the latter (11.4 %). Differences in the levels of the two fatty acids between artificial pellets and wild fry stomach contents suggest that dietary differences caused the observed differences in fry fatty acid composition. The levels of 18:2n-6 and 20:5n-3 in hatchery fry collected in coastal waters decreased and increased, respectively, within days after stocking in the river. Furthermore, the levels became similar to those of riverine wild fry by approximately 20 days after stocking. These results indicate that the two fatty acids can be used to distinguish between hatchery and wild chum salmon fry in the natural environment. However, the period during which the two can be distinguished is limited. • Artificial markings are used to distinguish between hatchery and wild fish. • Fatty acids contained in hatchery and wild salmon differed in natural environments. • The differences in fatty acid compositions disappeared over time.