Temperature, dye concentration, and exposure duration influence retention rates of Bismarck brown Y dye in small-bodied fish

Abstract Objectives Population estimates are critical for effective fisheries management but can be difficult to obtain for small, nongame fish species. Bismarck brown Y dye can be used to batch mark groups of small fish in mark–recapture studies, but little is known about factors influencing dye retention rates. Methods We conducted a laboratory experiment to assess the effect of Bismarck brown Y concentration (control, 1:50,000, and 1:10,000), dye exposure duration (1 and 2 h), and temperature (∼12.7°C, 16.5°C) on mark retention in Iowa Darter Etheostoma exile. For 9 d following dye exposure, we conducted blind assessments to assign individual fish as marked or unmarked and, when marked, also assigned a percent dye retention score (0–100%). We used generalized linear models to predict the influence of these factors on the mark status and dye retention scores as time elapsed. Results Bismarck brown Y dye mark status and percent retention scores were highest in the fish exposed to the high concentration and longest dye exposure time within the colder treatments (>9 d). Our results indicate that use of Bismarck brown Y dye to mark fish and conduct mark–recapture studies requires a clear understanding of how dyeing protocols and environmental factors (e.g., temperature) influence dye retention. Conclusion Our research provides an experimental framework for fisheries biologists to expand this technique to include additional species and a wider range of environmental conditions.