Comparison of three methods for marking a small floodplain minnow

Abstract

Background: Evaluation of the movement patterns of small-bodied fish is often hindered by the lack of a suitable long-term mark. We evaluated several techniques for long-term group and individual identification of adult (40-70 mm total length [TL]) Oregon chub (Oregonichthys crameri). We marked Oregon chub with one of two different sized passive integrated transponder (PIT) tags (a 9 × 2.12 mm, 0.067 g PIT tag [PIT-tag] or a 8.4 × 1.4 mm, 0.033 g PIT tag [PICO-tag]), a red visible implant elastomer (VIE) tag, or a freeze brand. We monitored survival, tag retention, and mark quality over 150 days. In addition, we assessed the minimum length and weight thresholds to achieve 80% and 90% survival of PIT-tagged fish. Results: Marking with a freeze brand, PICO-tag, or VIE tag had no effect on survival (P >0.05). In contrast, marking with a PIT-tag was associated with significantly lower (P <0.05) survival than in the control group. Survival was significantly higher (P = 0.002) for fish implanted with a PICO-tag than with the larger PIT-tag. The initial minimum TL for 80% and 90% survival was 54 mm and 64 mm TL, respectively, for the PIT-tag treatment. The 90% survival threshold for PICO-tagged fish was 44 mm TL. The 80% survival threshold was outside the range of sizes used in our experiment (<40 mm TL). Similarly, the 80% and 90% survival weight thresholds for the PIT-tag treatment were 1.5 g and 2.4 g, respectively, and the 90% survival threshold for PICO-tagged fish was 0.9 g. Tag retention was 94% and 95% in the PIT-tag and PICO-tag treatments, respectively; 80% of the freeze branded fish had easily recognizable tags after 150 days and 88% of the fish marked with VIE had easily recognizable tags after 150 days. Conclusions: PICO-tags, VIE marks, and freeze brands are all feasible long-term marking techniques for Oregon chub with negligible effects on survival through 150 days. The selection of a particular technique should be based on the study design and objectives (e.g., individual versus group identification), cost, ease, speed of tagging, and survival.