This larval zebrafish has two useful genetic modifications. Green fluorescent protein (GFP) is synthesized by neurons in the brain and spinal cord which use the neurotransmitter glutamate. This protein, originally isolated from jellyfish, displays green fluorescence when exposed to blue light. In this case, GFP labeling will be used to visually target individual neurons for further study. The fish also lacks particular pigment-producing cells, and is almost completely transparent. This makes it easy to directly image through the entire, living fish, as shown here.