Marking is accomplished by embedding fluorescent pigment into the dermal tissue of fish with compressed air. The principal species evaluated were largemouth bass, Micropterus salmoides, bluegill, Lepomis macrochirus, redear sunfish, Lepomis microhophus, and channel catfish, Ictalurus punctatus. Marking rate was approximately 1500-2000 fingerling size fish per hour with a two-".,'m team. Mark detection requires ultraviolet light. Air pressure and application distance are critical factors in marking success. Best results were obtained using an air pressure range of 85-200 psi from a distance of 12 to 18 inches. After 9 months mark retention on largemouth bass and bluegi II was 95% and 96.8% respectively. Redear exhibited 100% pigment retention for an 11 month period. Mark retention on channel catfish was 100% during a 10 month experiment. Results indicate marks will be retained by certain species for a much longer period, although mark quality will reduce with time. Mortality resulting from marking was negligible.