MoTP, known more formally as 4-(4-morpholinobutylthio)phenol, is used to ablate larval melanocytes in zebrafish in order to study melanocyte regeneration. MoTP is converted to a cytotoxin in cells with high tyrosinase activity, which in the zebrafish embryo are limited to melanoblasts and newly formed melanocytes. The wash-out of MoTP allows regeneration through the proliferation of melanocyte stem cells.