How Do Zebrafish Get Their Stripes?

Zebrafish owe their name to the beautiful striped blue and gold pattern they adorn, and for the first time scientists have gained a deeper understanding of how these fish form their characteristic colors, a new study describes.

This small freshwater fish possesses three major pigment cell types: black cells, reflective silvery cells, and yellow cells. Previous research has determined that these cell types emerge during growth in the skin of the tiny juvenile fish, and arrange as a multilayered mosaic to make the stripes that we see. While it was known that all three cell types have to interact to form proper stripes, until now, scientists didn't understand the embryonic origins of these cells.

Described in the journal Science, researchers from the Max Planck Institute for Developmental Biology in Tübingen, Germany used an advanced microscope to observe juvenile fish and stripe formation for up to three weeks. These living, growing fish have fluorescently labeled pigment cell precursors that the researchers looked for, allowing them to trace the multiplication, migration and spreading of individual cells as their stripes formed.

Surprisingly, the analysis revealed that the three cell types reach the skin by completely different routes. The yellow cells originate from the dorsal side of the fish embryo, whereas the black and reflective silvery cells are located close to the spinal chord in the developing zebrafish.

"We were surprised to discover that they divide and multiply as differentiated cells to cover the skin of the fish before the silvery and black cells arrive to form the stripes," co-author Brigitte Walderich said in a statement.

In particular, the yellow cells undergo dramatic changes in cell shape to tint the stripe pattern of zebrafish.

"We were surprised to observe such cell behaviors, as these were totally unexpected from what we knew about color pattern formation," added first author Prateek Mahalwar.

What's more, both the silvery and yellow cells are able to switch cell shape and color, depending on their location, yielding the blue-tinted and goldish hues we know zebrafish for.