Immersion in Neutral Red Solution as a Mass-Marking Technique to Study the Movement of the Amphipod Corophium Volutator

We evaluated the usefulness of immersion in neutral red solution as a marking technique for studies of movement of the amphipod Corophium volutator. Amphipods were immersed for 20 minutes in solutions of neutral red at different concentrations (25, 50 and 100 mg L−1). Amphipods incorporated dye at all concentrations, and the hepatopancreas remained distinctly stained red for at least 7 days. No increase in mortality was detected at any concentration when compared to a control treatment (0 mg L−1). In a separate field experiment, staining did not significantly affect tendency of C. volutator to move. Overall, immersion in neutral red seems to be an appropriate technique to rapidly mark large numbers of C. volutator and is suitable for short-term mark-recapture experiments. This technique may also apply to other small-sized crustacean species with relatively transparent exoskeletons.