Eels are elongated fish, ranging in length from 5 cm in the one-jawed eel to 4 m in the slender giant moray. Adults range in weight from 30 g to well over 25 kg. They possess no pelvic fins, and many species also lack pectoral fins. The dorsal and anal fins are fused with the caudal fin, forming a single ribbon running along much of the length of the animal. Eels swim by generating body waves which travel the length of their bodies. They can swim backwards by reversing the direction of the wave.