Long-Term Retention and Visibility of Visible Implant Elastomer Tags in Brook Trout

Abstract

Understanding how juvenile brook trout Salvelinus fontinalis from different sources contribute to fishable populations would be facilitated by a batch mark that could be applied to early life stages and be retained and visible throughout a fish's life. We evaluated visible implant elastomer (VIE) as a long-term batch mark for juvenile brook trout in hatchery and lake environments. Visible implant elastomer material was injected into the postocular eye tissue of 2,350 age-0 brook trout. Marked fish were stocked into three lakes, and an additional group was held in the hatchery. Tissue dissections revealed that VIE tag retention was 100% in both environments after 970 d. Tag visibility in hatchery fish examined under indoor fluorescent light was greater than 95% through 585 d, then dropped to 55–70% between 700 and 900 d. Tag visibility in lake fish examined under outdoor sunlight was 50–72% at 400 d and 0% at 959 d. When these same fish were observed in dark conditions with blue-filtered light and amber glasses, tag visibility was 75% for hatchery fish at 970 d and 100% for lake fish at 959 d. The high retention and increased visibility when viewed in dark conditions with blue-filtered light demonstrates that VIE tags are a suitable long-term batch mark for juvenile brook trout.