Retention of Visible Implant Tags in Lake Trout and Atlantic Salmon

Abstract

Abstract Retention and readability of visible implant (VI) tags were evaluated in adult (2-yearold) Atlantic salmon (Salmo salar), adult (4-year-old) lake trout (Salvelinus namaycush), and yearling (10-month-old) fish of both species. Tags were implanted in adipose eyelid tissue posterior to the eye. After 10 months, retention in yearlings was 49% by Atlantic salmon and 41% by lake trout. In adults, retention was 84% by Atlantic salmon and 45% by lake trout. Tag retention in yearling Atlantic salmon increased with fish weight at tagging; tag retention, by weight-groups, was 0% for fish that weighed 20 g or less; 46% for 21–40-g fish; and 71% for 41–99-g fish. Tag retention in adults of Atlantic salmon and lake trout was not related to fish weight. After 10 months, the percentage of readable tags was 100% in yearling Atlantic salmon and 82% in adult Atlantic salmon, and 0% in yearling lake trout and 77% in adult lake trout. None of the tags in yearling lake trout were readable 294 d after implant, because of cloudiness of the adipose eyelid tissue. Tags recovered from fish with cloudy adipose tissue were readable. The proportion of total tag loss occurring in the first 70 d after tagging was 78% in yearling Atlantic salmon and 22% in adult Atlantic salmon, and 67% in yearling lake trout and 41% in adult lake trout. An illuminated magnifier lamp (1.7 × magnification) greatly increased the readability of the VI tags. The VI tags were effective for Atlantic salmon larger than 30 g, but they were not effective for lake trout.