Zebrafish have proven to be a crucial model for biological elucidations, especially heart-disease studies, owing to their remarkable regeneration capacity. Other than conventional methods, monitoring of electrocardiogram (ECG) has shown promising results recently; however, experiments were usually carried out with sedated fish, resulting in affected signals. In this work, wireless power transfer (WPT) via inductive coupling is developed to power our previously-reported miniaturized ECG sensor implanted in an adult zebrafish. This would enable continuous monitoring of freely-swimming fish without disrupting their normal activities. The WPT is achieved using inductive coupling with the transmitter (TX) located around the fish tank, and a solenoid embedded in the fish implant as the receiver (RX), with sizes of Φ77 mm × 10 mm and Φ1 mm × 10 mm, respectively. Power transfer efficiency (PTE) and an adaptive tuning method were characterized using a Vector Network Analyzer (VNA) via S-parameter measurement to ensure the ECG sensor will receive sufficient power for operating and communication.