This paper presents a novel approach to the long-term recording of electrocardiogram (ECG) signals in prawns, including a 3-lead electrode, a lightweight external wires assembly, a waterproof electrode-wire junction, and a standardized implanting procedure. The proposed low-cost device is easily constructed, even by untrained undergraduate students, using common laboratory materials. Consistent ECG recordings were obtained over a period of 72 h in experiments on 6 freely moving prawns (Macrobrachium rosenbergii). A subsequent experiment conducted continuously for 38 d revealed that despite gradual attenuation the ECG signals could still be identified (signal-to-noise ratio ≥3). The prawns survived implantation and later underwent natural molting, whereupon the electrode was successfully re-implanted. The proposed electrode is a valuable tool by which to gain insight into the long-term physiological state of crustaceans.