Encapsulation and migration of PIT tags implanted in brown trout (Salmo trutta L.)

Passive integrated transponder (PIT) tags are used to identify individual fishes in fish hatcheries, and to monitor habitat use, spatial movements and migratory patterns in the field. The tags are relatively inexpensive, easy to implant, and are thought to have long retention times. However, implanted tags may also invoke tissue reactions that result in their encapsulation by connective tissue. The present study examined the encapsulation of small (12 mm) and larger (23 mm) PIT tags implanted into the peritoneal cavity of brown trout (Salmo trutta). After 8 and 12 months, respectively, all 12 mm and 23 mm tags were encapsulated, but many had migrated away from the point of injection to regions that included the lumen of the intestine, the liver and heart, as well as the kidneys. The presence of PIT tags in the lumen of the intestine suggests that the gastrointestinal (GI) tract is a potential route of PIT tag expulsion by brown trout. The possibility of such adverse events may have to be considered where PIT tags are to be used in longer-term studies of this fish in aquaculture, laboratory or field settings.