Abstract
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The retention and readability of visible implant (VI) tags
were evaluated in juvenile brown trout. The tags were implanted in the
adipose eyelid tissue posterior to the left eye, in a total of 6697 fish in
18 groups. During the first year, tag retention increased with tagging
experience, from 58 to 64% in 3-summer-old fish and from 86 to 96% in
4-summer-old fish. The effect of fish size at tagging on tag loss was clear
in the 3-summer-old groups in 1991 (ANOVA, P=0.00001). Tag retention
in 3-year-old and 4-summer-old fish in 1992 and 1993 varied from 96 to 99%
and the handling of the fish after tagging affected retention significantly
(t-test, p=0.0002), the average being 98.7% for those
transposed by submerging and 96.5% in those transposed by dropping. After
inspection the fish were released into a natural environment. On recapture
after 6 months or more the red tags (faded almost to white) and yellow tags
(originally close to white) were difficult to distinguish. No infection or
tissue damage was found after either inspection or stocking. |