All fish are known to change colors when stressed. Most of the time this is a whiting out or a dulling of their colors. In pet stores almost all fish are stressed. The tanks are crowded and often contain diseases. While the cold cups may not always contain disease, they will stress tropical fish like betta. And just like any other fish, the colors of the betta will dull and fade. The transformation from stressed fish to unstressed fish can take a matter of hours or sometimes days. This is the main reason betta change color when you first get them.
|This is the same betta. On the left is the betta in a cold cup in the store. |
On the right is after a month of being in clean, warm water.
Often the fish you see sold in store aren't very old. Typically the smaller they are, the younger they are. Their colors haven't fully developed yet and neither have their fins. So essentially what you are buying is a "work in progress." Some will change more than others as not all bettas being sold are the same age. Below is a very young betta that I bought in July 2011.
|This image shows the same betta from July 2011 to February 2012. |
Notice the longer fins and more pronounced color.
Some betta carry what is called the marble gene. This gene sequence causes the betta's colors to changing even after they should have stabilized with age. Sometimes the betta will continue to change his whole life even looking like a whole different fish a year after you buy him or her. Sometimes the betta will "marble out" and become a cellophane, and some "unmarble" and turn a dark, solid color. There is no way to predict what you will end up with. This presents an interesting challenge to breeders, and they can be a neat fish to have as a pet. A month later you can end up with a completely different fish than you started with!
|This is my marble plakat. The image on the right is from July 2012. The middle image is a |
month later. The far right image is from October 2012. My marble has unmarbled
to a beautiful solid blue.
Parnell, Victoria. 3 Mar 2006. "The Ever-Changing Marble." bettysplendens.com. Retrieved 4 Nov 2012.