This dataset contains measurements of photosynthetic efficiency, expressed as maximum quantum yield (Fv/Fm), of the endosymbiotic diatoms within the benthic foraminifera Amphistegina lobifera, exposed to electric currents over a one-month period. The data were collected in May 2023, the second of a two-part experiment, using Imaging Pulse-Amplitude Modulated (PAM) fluorometry. These measurements offer valuable insights into how electric currents influence the physiology of the endosymbionts of Amphistegina lobifera.