Zebrafish Injectable Plastic for Identification Tagging (ZIP IT) for larvae to adults using a fluorescent Visible Implant Elastomer

Distinguishing individuals or small groups is essential for many experiments. The regenerative properties of zebrafish make traditional marking methods for rodent models (e.g., tattoos, tissue clipping) ineffective. Fluorescent Visible Implant Elastomer (VIE) can permanently mark juvenile and adult zebrafish but to date no marking technique has been described for larval stage zebrafish. This protocol, Zebrafish Injectable Plastic for Identification Tagging (ZIP IT), utilizes VIE in zebrafish as early as 2 days post fertilization (dpf) using standard microinjection methods and direct injection using an insulin syringe at one month. Larval zebrafish between 2 and 7 dpf were injected in the dorsal musculature. At one month, retention and visibility of the VIE was observed in 72% of the injected fish with no effect on growth; however, a variable change in mortality was observed, generally higher than the uninjected fish. This demonstrates that VIE can be used in very early stages of fish development, providing the first procedure to track individuals or groups within a larger population. Subcutaneous injection of juvenile zebrafish starting at one month has greater than 99%-mark retention and visibility with very low mortality. The combination of larvae and juvenile VIE injections also provide a powerful tool to track and gather data from marked fish throughout their lifespan. • We present a method for tagging individuals or groups of zebrafish at most life stages (larvae or juvenile/adult) with Visible Implant Elastomer (VIE). • The larvae and juvenile injection procedures can be combined so that an individual fish can be tagged for its entire lifetime. Larvae injections become significantly less visible after one month; however, the fish can be reinjected using the juvenile procedure, thus allowing continuity of the visible mark. • This protocol was empirically built on the “Evaluation of VIE tags in Zebrafish (Danio rerio)” by Hohn and Petrie-Hanson (2013) and expanded to include larvae and a small batch elastomer mixing technique.