I am currently working with Daphnia magna (small marine crustaceans) and need to monitor their heart rate using a stroboscope, as it beats to quickly to count individually. Using a stroboscope and a cold light source, I should be able to change the frequency of the stroboscope in order to make the Daphnia heart appear to be 'frozen'. Using this information, how do I finally work out bpm using the frequency?

Thanks beforehand if anybody could help me out!