The Digital Fish Library

Thunniform swimmers use very little body musculature for forward propulsion. Instead, thrust is generated almost exclusively by a high, stiff, deeply forked caudal fin mounted on a narrow caudal peduncle. Most movement is with the tail and the anterior body remains relatively immobile. Thunniform locomotion is an extreme form of carangiform swimming, representing an evolutionary trend towards greater speed both in terms of burst swimming and sustained swimming. .