Materials Mature zebrafish Zebrafish Embryo Solution Retinoic acid (all-trans-retinoic acid) – stock concentration 10-4 M in DMSO DMSO 60 mm glass Petri dishes (4) Siphon Fine fry net or mesh filter Zebrafish embryos at dome / 30% epiboly stage Tricaine Dissecting microscope and camera Incubator (28°C) Procedure Obtain dome stage (4.3 hours post-fertilization at room temperature) zebrafish embryos (Isolation of Zebrafish Embryos) Dilute retinoic acid stock into the following titrate concentrations using Zebrafish Embryo Medium: 10-8 M (1.0 µL stock solution in 10 mL Zebrafish Embryo Medium) 10-10 M (100 µL 10-8 M solution in 10 mL Zebrafish Embryo Medium) 10-11 M (10 µL 10-8 M solution in 10 mL Zebrafish Embryo Medium) Place approximately 5 mL of each titration into an appropriately labeled Petri dish. For the control, use 5 mL of Zebrafish Embryo Medium. Place 10 -15 zebrafish embryos in each Petri dish. Incubate embryos at 28°C for 24-26 hours. Obtain results by photographing the embryos the next day and as often afterwards as is possible, until hatching. The embryos may need to be dechorionated, which may be done under the dissecting microscope with clean fine forceps by gently tearing the chorion and allowing the embryo to pass though. When photographing older or hatched embryos, Tricaine may be used as an anesthetic to immobilize the embryos When finished with the experiment, the embryos may be euthanized by pouring them over ice.