A fish killing and fish tissue sanitizing apparatus includes a tank, a water feed pipe extending to the tank, and an electromechanical transducer in pressure-wave transmitting relationship to the tank for generating ultrasonic pressure waves in water contained in the tank. An electrical signal generator is operatively connected to the transducer for energizing same with an alternating electrical signal. A sensor is in operative contact with water contained in the tank for detecting transient and inertial cavitation occurring within the water in the tank.