High‐Pressure Injection of Photonic Paint to Mark Adult Chinook Salmon

Photonic paint (polymethylacrylate fluorescent pigment encapsulated in latex microspheres) was applied with a pressurized injection system (42.2 kg/cm2) to adult chinook salmon Oncorhynchus tshawytscha during artificial spawning to color mark three portions: The pectoral girdle, the pectoral fin, and the base of the dorsal fin. The criteria used to evaluate these marks were relative ease of application and identification, mark retention, marking mortality, and cost. Color marks in the pectoral girdle were relatively easy to apply, noninvasive, and easily identified by the evaluator. Mean retention time for girdle marks was 45 d; some marks were retained up to 56 d; and 100% of the marks were readable. In comparison, only 57% of the pectoral fin marks and 37% of the dorsal fin marks were readable. Mark rate averaged 30 s for each mark type (90 s for each fish) at a cost of US.24/mark. No additional mortality was associated with marking compared with overall prespawn mortality (23.3% versus 23.6%, respectively). We concluded that color marking adult salmonids in the pectoral girdle is a viable alternative to current marking options.