Colour marking of small fish with a marking stand for DermojetⓇ.

We designed a marking stand for the Dermojet Ⓡ , which substantially improves fish marking via needleless subcutaneous injection of dye. The marking stand allows to increase the nozzle-to-fish distance, adjust this position and to keep the jet injector fixed during operation as well as dye refilling. A laser pointer enables a precise and small-scale aiming. Using this marking stand we marked the caudal fin of small fish with Alcian blue for a flume experiment. In total we marked 204 gudgeon (Gobio gobio) and spirlin (Alburnoides bipunctatus) of 9-14 cm length with up to two dots per fish. Weighing, measuring and marking one sedated fish took 30 to 60 s. Immediate marking success was 100%. Fish were kept indoors in tanks for 7-12 days post-marking and the colour mark remained visible for the complete study period. During our flume experiment the colour marks at the caudal fin were detectable on all fish regardless of swimming position. With this easy and fast method fish can be marked gently, reliably and efficiently.•Application of a high-pressure jet injector for needleless and accurate colour marking of fish.•Manual for marking the caudal fin of small fish with Alcian blue.