Tc. Hughes et al., Comparison of large and small visible implant tags: Retention and readability in hatchery brook trout, N AM J AQUA, 62(4), 2000, pp. 273-278
Retention and readability of small (2.5 X 1.0 X 0.1-mm) and large (3.0 X 1.
5 X 0.1-mm) visible implant (VI) tags were compared among different size-cl
asses (211-470 mm total length, TL) of hatchery brook trout Salvelinus font
inalis. Among smaller size-groups (<400 mm TL), retention of large tags (63
-86%) 100 d after tagging was less than retention of small tags (89-97%). O
verall retention of large tags was much better among larger size-groups (<g
reater than or equal to>400 mm TL) than among smaller sizes (97% versus 74%
). Insufficient postorbital adipose tissue in smaller size-groups probably
caused the poor retention of large VI tags. Retention was different between
the two workers who inserted large VI tags. Readability of large and small
tags was not affected by fish size at tagging. We recommend that large VI
tags be used to mark brook trout longer than 400 mm TL because they are ret
ained better. Fish with small tags from a previous study were subsequently
monitored (and reported here) to assess retention and readability between 3
54 and 454 d after tag insertion. Over this period less than 3% of small VI
tags were lost, but readability declined from 95% to 74%. In studies that
extend beyond a year, small VI tags may have to be extracted to be read.