How to track spermatozoa using high-speed visual feedback

In this paper, we report how to track quickly and vigorously swimming ascidian spermatozoa using high-speed visual feedback at a frame rate of 1 kHz. Ascidian spermatozoa swim as fast as 300 μm/s by rotating their flagella 50 times/s. This vigorous swimming style has prevented stable image observation and made it difficult to track them reliably with our previously developed visual tracking system. Here, we describe how we overcame these problems using image processing techniques to achieve stable tracking of fast, small ascidian spermatozoa for more than 180 s using high-speed visual feedback.