Fluorescent granular pigment sprayed with 738 g/cm² (105 p.s.i .) for 5, 10, 20 second intervals was used to mark crayfish in a laboratory study. The pigment was retained by 100% of the unmolted crayfish 35 days after treatment and by 65% of the crayfish 56 days after treatment. Crayfish which were induced to molt after being sprayed generally lost the fluorescent pigment during the molt. Mortality, (2%), due to the marking procedures was minimal. / Master of Science