Sporting a fresh coat of tan, these juvenile Chinook salmon look like they are ready for summer. Actually, these fish were just removed from a color bath of Bismarck brown dye. Dye submersion is a widely used technique for externally marking large groups of fish. Instead of injecting the dye into a fin to create a mark, the fish are immersed in a dilution of dye. Depending on the type of dye and the fish species, a recognizable mark can last from a couple of days to several weeks. These salmon are now ready to be released back into the river for a rotary screw trap efficiency test. Won’t the other fish be jealous?