Growth, Mortality, and Mark Retention of Hatchery Brook Trout Marked with Visible Implant Tags, Jaw Tags, and Adipose Fin Clips

Abstract Growth, mortality, mark retention, and mark readability were compared among control and treatment groups of 197–265-mm hatchery brook trout Salvelinus fonitinalis marked with visible implant (VI) tags, adipose tin (AD) clips, or stainless steel circularstrap jaw tags. Based on growth rates calculated for individual fish after 90 d, brook trout marked with VI tags grew faster than those with jaw tags (P G 0.03). Mortality was higher after 251 d for jaw-tagged fish (45%) than the cumulative mortality (8.3%) observed among VI-tagged, AD clipped, and control fish, Mark retention was 759c for VI tags, 99% for jaw tags, and 100% for AD clips, Visible implant tag loss was greatest within 7 d after insertion. After 251 d. 37% of the VI tags were unreadable. but 92% of the “unreadable” tags were readable if magnification and light were used. Unreadability could limit the usefulness of VI tags in multiyear studies unless problem tags can be removed from the fish to read tag codes.