The effects of external ultrasonic tagging on the swimming performance of rainbow trout, Salmo gairdneri Richardson

The effects of externally mounted ultrasonic tags on the tail beat frequency (TBF) and opercular beat rate (OBR) of rainbow trout was measured at different swimming speeds. The increase in relative drag caused by the tags was also measured. Two tag types were used: one where both the circuitry and the battery were in a single package mounted on one side of the fish, the other where they were in two packages mounted symmetrically on either side of the fish. Both tag types raised both TBF and OBR. Of the two, the symmetrical tag effects behaviour less, especially at low swimming speeds, even though it causes a greater increase in relative drag.