Evaluation of injectable fluorescent tags for marking centrarchid fishes: Retention rate and effects on vulnerability to predation

We evaluated the performance of injectable fluorescent tags for use in mass marking of centrarchid fishes. Using age-0 largemouth bass Micropterus salmoides and bluegills Lepomis macrochirus (50-100 mm total length), we compared (1) the retention rate of injectable photonic dyes (IPDs) applied to the fin rays of largemouth bass, (2) retention rates of IPDs versus visible implant elastomers (VIEs), and (3) the effect of colorless and brightly colored marks on prey selectivity by adult largemouth bass. Retention rate of IPDs declined appreciably in age-0 largemouth bass (50 mm) after 120 d with only 19% of fish retaining visible marks by that time. By the end of the experiment (day 310), no marks were visible in anal fin rays of largemouth bass. For larger age-0 largemouth bass (100 mm), retention rates of IPDs after 48 d were greatest for fish marked in the anal fin (40%), followed by caudal (20%) and dorsal fin (5%) markings. Visible implant elastomers were retained at a higher rate (84.4%) than IPDs (68.4%) and were easier to observe after 210 d when placed in subcutaneous, opercular tissue. In general, bluegills marked with brightly colored tags were selected at a greater rate by largemouth bass than were fish marked with cryptic colors. Mean prey selectivities (Manly's alpha) were higher for brightly colored marks (blue = 0.36 and pink = 0.35) than for cryptic marks (colorless = 0.28). Only VIE marks had retention rates long enough for use in small centrarchlds (<150 mm), but application of brightly colored marks to conspicuous areas should be avoided because that may increase susceptibility of the tagged fish to predation.